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1968 – Douglas Engelbart demonstrated NLS, a system which uses a mouse, pointers, hypertext, and multiple windows.
1970 – Researchers at Xerox Palo Alto Research Center (many from SRI) develop WIMP paradigm (Windows, Icons, Menus, Pointers)
1973 – Xerox Alto: commercial failure due to expense, poor user interface, and lack of programs
1979 – Steve Jobs and other Apple engineers visit Xerox PARC. Though Pirates of Silicon Valley dramatizes the events, Apple had already been working on developing a GUI, such as the Macintosh and Lisa projects, before the visit.
1981 – Xerox Star: focus on WYSIWYG. Commercial failure (25K sold) due to cost ($16K each), performance (minutes to save a file, couple of hours to recover from crash), and poor marketing
1982 – Rob Pike and others at Bell Labs designed Blit, which was released in 1984 by AT&T and Teletype as DMD 5620 terminal.
1984 – Apple Macintosh popularizes the GUI. Super Bowl commercial shown twice, was the most expensive commercial ever made at that time
1984 – MIT's X Window System: hardware-independent platform and networking protocol for developing GUIs on UNIX-like systems
1985 – Windows 1.0 – provided GUI interface to MS-DOS. No overlapping windows (tiled instead).
1985 – Microsoft and IBM start work on OS/2 meant to eventually replace MS-DOS and Windows
1986 – Apple threatens to sue Digital Research because their GUI desktop looked too much like Apple's Mac.
1987 – Windows 2.0 – Overlapping and resizable windows, keyboard and mouse enhancements
1987 – Macintosh II: first full-color Mac
1988 – OS/2 1.10 Standard Edition (SE) has GUI written by Microsoft, looks a lot like Windows 2
Interface design
Primary methods used in the interface design include prototyping and simulation.
Typical human–machine interface design consists of the following stages: interaction specification, interface software specification and prototyping:
Common practices for interaction specification include user-centered design, persona, activity-oriented design, scenario-based design, and resiliency design.
Common practices for interface software specification include use cases and constrain enforcement by interaction protocols (intended to avoid use errors).
Common practices for prototyping are based on libraries of interface elements (controls, decoration, etc.).
Principles of quality | User interface | Wikipedia | 498 | 45249 | https://en.wikipedia.org/wiki/User%20interface | Technology | User interface | null |
In broad terms, interfaces generally regarded as user friendly, efficient, intuitive, etc. are typified by one or more particular qualities. For the purpose of example, a non-exhaustive list of such characteristics follows:
Clarity: The interface avoids ambiguity by making everything clear through language, flow, hierarchy and metaphors for visual elements.
Concision: However ironically, the over-clarification of information—for instance, by labelling the majority, if not the entirety, of items displayed on-screen at once, and regardless of whether or not the user would in fact require a visual indicator of some kind in order to identify a given item—can, and, under most normal circumstances, most likely will lead to the obfuscation of whatever information.
Familiarity: Even if someone uses an interface for the first time, certain elements can still be familiar. Real-life metaphors can be used to communicate meaning.
Responsiveness: A good interface should not feel sluggish. This means that the interface should provide good feedback to the user about what's happening and whether the user's input is being successfully processed.
Consistency: Keeping your interface consistent across your application is important because it allows users to recognize usage patterns.
Aesthetics: While you do not need to make an interface attractive for it to do its job, making something look good will make the time your users spend using your application more enjoyable; and happier users can only be a good thing.
Efficiency: Time is money, and a great interface should make the user more productive through shortcuts and good design.
Forgiveness: A good interface should not punish users for their mistakes but should instead provide the means to remedy them.
Principle of least astonishment
The principle of least astonishment (POLA) is a general principle in the design of all kinds of interfaces. It is based on the idea that human beings can only pay full attention to one thing at one time, leading to the conclusion that novelty should be minimized.
Principle of habit formation
If an interface is used persistently, the user will unavoidably develop habits for using the interface. The designer's role can thus be characterized as ensuring the user forms good habits. If the designer is experienced with other interfaces, they will similarly develop habits, and often make unconscious assumptions regarding how the user will interact with the interface.
A model of design criteria: User Experience Honeycomb | User interface | Wikipedia | 481 | 45249 | https://en.wikipedia.org/wiki/User%20interface | Technology | User interface | null |
Peter Morville of Google designed the User Experience Honeycomb framework in 2004 when leading operations in user interface design. The framework was created to guide user interface design. It would act as a guideline for many web development students for a decade.
Usable: Is the design of the system easy and simple to use? The application should feel familiar, and it should be easy to use.
Useful: Does the application fulfill a need? A business's product or service needs to be useful.
Desirable: Is the design of the application sleek and to the point? The aesthetics of the system should be attractive, and easy to translate.
Findable: Are users able to quickly find the information they are looking for? Information needs to be findable and simple to navigate. A user should never have to hunt for your product or information.
Accessible: Does the application support enlarged text without breaking the framework? An application should be accessible to those with disabilities.
Credible: Does the application exhibit trustworthy security and company details? An application should be transparent, secure, and honest.
Valuable: Does the end-user think it's valuable? If all 6 criteria are met, the end-user will find value and trust in the application.
Types | User interface | Wikipedia | 246 | 45249 | https://en.wikipedia.org/wiki/User%20interface | Technology | User interface | null |
Attentive user interfaces manage the user attention deciding when to interrupt the user, the kind of warnings, and the level of detail of the messages presented to the user.
Batch interfaces are non-interactive user interfaces, where the user specifies all the details of the batch job in advance to batch processing, and receives the output when all the processing is done. The computer does not prompt for further input after the processing has started.
Command line interfaces (CLIs) prompt the user to provide input by typing a command string with the computer keyboard and respond by outputting text to the computer monitor. Used by programmers and system administrators, in engineering and scientific environments, and by technically advanced personal computer users.
Conversational interfaces enable users to command the computer with plain text English (e.g., via text messages, or chatbots) or voice commands, instead of graphic elements. These interfaces often emulate human-to-human conversations.
Conversational interface agents attempt to personify the computer interface in the form of an animated person, robot, or other character (such as Microsoft's Clippy the paperclip), and present interactions in a conversational form.
Crossing-based interfaces are graphical user interfaces in which the primary task consists in crossing boundaries instead of pointing.
Direct manipulation interface is a general class of user interfaces that allow users to manipulate objects presented to them, using actions that correspond to the physical world, at least loosely.
Gesture interfaces are graphical user interfaces which accept input in a form of hand gestures, or mouse gestures sketched with a computer mouse or a stylus.
Graphical user interfaces (GUI) accept input via devices such as a computer keyboard and mouse and provide articulated graphical output on the computer monitor. There are at least two different principles widely used in GUI design: Object-oriented user interfaces (OOUIs) and application-oriented interfaces.
Hardware interfaces are the physical, spatial interfaces found on products in the real world from toasters, to car dashboards, to airplane cockpits. They are generally a mixture of knobs, buttons, sliders, switches, and touchscreens.
provide input to electronic or electro-mechanical devices by passing a finger through reproduced holographic images of what would otherwise be tactile controls of those devices, floating freely in the air, detected by a wave source and without tactile interaction. | User interface | Wikipedia | 474 | 45249 | https://en.wikipedia.org/wiki/User%20interface | Technology | User interface | null |
Intelligent user interfaces are human–machine interfaces that aim to improve the efficiency, effectiveness, and naturalness of human–machine interaction by representing, reasoning, and acting on models of the user, domain, task, discourse, and media (e.g., graphics, natural language, gesture).
Motion tracking interfaces monitor the user's body motions and translate them into commands, currently being developed by Apple.
Multi-screen interfaces, employ multiple displays to provide a more flexible interaction. This is often employed in computer game interaction in both the commercial arcades and more recently the handheld markets.
Natural-language interfaces are used for search engines and on webpages. User types in a question and waits for a response.
Non-command user interfaces, which observe the user to infer their needs and intentions, without requiring that they formulate explicit commands.
Object-oriented user interfaces (OOUI) are based on object-oriented programming metaphors, allowing users to manipulate simulated objects and their properties.
Permission-driven user interfaces show or conceal menu options or functions depending on the user's level of permissions. The system is intended to improve the user experience by removing items that are unavailable to the user. A user who sees functions that are unavailable for use may become frustrated. It also provides an enhancement to security by hiding functional items from unauthorized persons.
Reflexive user interfaces where the users control and redefine the entire system via the user interface alone, for instance to change its command verbs. Typically, this is only possible with very rich graphic user interfaces.
Search interface is how the search box of a site is displayed, as well as the visual representation of the search results.
Tangible user interfaces, which place a greater emphasis on touch and physical environment or its element.
Task-focused interfaces are user interfaces which address the information overload problem of the desktop metaphor by making tasks, not files, the primary unit of interaction.
Text-based user interfaces (TUIs) are user interfaces which interact via text. TUIs include command-line interfaces and text-based WIMP environments.
Touchscreens are displays that accept input by touch of fingers or a stylus. Used in a growing amount of mobile devices and many types of point of sale, industrial processes and machines, self-service machines, etc.
Touch user interface are graphical user interfaces using a touchpad or touchscreen display as a combined input and output device. They supplement or replace other forms of output with haptic feedback methods. Used in computerized simulators, etc. | User interface | Wikipedia | 510 | 45249 | https://en.wikipedia.org/wiki/User%20interface | Technology | User interface | null |
Voice user interfaces, which accept input and provide output by generating voice prompts. The user input is made by pressing keys or buttons, or responding verbally to the interface.
Web-based user interfaces or web user interfaces (WUI) that accept input and provide output by generating web pages viewed by the user using a web browser program.
Zero-input interfaces get inputs from a set of sensors instead of querying the user with input dialogs.
Zooming user interfaces are graphical user interfaces in which information objects are represented at different levels of scale and detail, and where the user can change the scale of the viewed area in order to show more detail. | User interface | Wikipedia | 132 | 45249 | https://en.wikipedia.org/wiki/User%20interface | Technology | User interface | null |
The bonobo (; Pan paniscus), also historically called the pygmy chimpanzee (less often the dwarf chimpanzee or gracile chimpanzee), is an endangered great ape and one of the two species making up the genus Pan (the other being the common chimpanzee, Pan troglodytes). While bonobos are, today, recognized as a distinct species in their own right, they were initially thought to be a subspecies of Pan troglodytes, because of the physical similarities between the two species. Taxonomically, members of the chimpanzee/bonobo subtribe Panina—composed entirely by the genus Pan—are collectively termed panins.
Bonobos are distinguished from common chimpanzees by relatively long limbs, pinker lips, a darker face, a tail-tuft through adulthood, and parted, longer hair on their heads. Some individuals have sparser, thin hair over parts of their bodies. The bonobo is found in a area within the Congo Basin of the Democratic Republic of the Congo (DRC), Central Africa. It is predominantly frugivorous, compared to the often highly omnivorous diets and hunting of small monkeys, duiker and other antelope exhibited by common chimpanzees. Bonobos inhabit primary and secondary forest, including seasonally inundated swamp forest. Because of political instability in the region, and the general timidity of bonobos, there has been relatively little field work done observing the species in its natural habitat.
According to studies published in 2017 by researchers at The George Washington University, the ancestors of the genus Pan split from the human line about 8 million years ago; moreover, bonobos split from the common chimpanzee line about 2 million years ago. | Bonobo | Wikipedia | 375 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
Along with the common chimpanzee, the bonobo is the closest extant relative to humans. As the two species are not proficient swimmers, the natural formation of the Congo River (around 1.5–2 million years ago) possibly led to the isolation and speciation of the bonobo. Bonobos live south of the river, and thereby were separated from the ancestors of the common chimpanzee, which live north of the river. There are no concrete figures regarding population, but the estimate is between 29,500 and 50,000 individuals. The species is listed as Endangered on the IUCN Red List and is most threatened by habitat destruction, human population growth and movement (as well as ongoing civil unrest and political infighting), with commercial poaching being, by far, the most prominent threat. Bonobos typically live 40 years in captivity; their lifespan in the wild is unknown, but it is almost certainly much shorter.
Etymology
Formerly the bonobo was known as the "pygmy chimpanzee", despite the bonobo having a similar body size to the common chimpanzee. The name "pygmy" was given by the German zoologist Ernst Schwarz in 1929, who classified the species on the basis of a previously mislabeled bonobo cranium, noting its diminutive size compared to chimpanzee skulls.
The name "bonobo" first appeared in 1954, when Austrian zoologist Eduard Paul Tratz and German biologist Heinz Heck proposed it as a new and separate generic term for pygmy chimpanzees. The name is thought to derive from a misspelling on a shipping crate from the town of Bolobo on the Congo River near the location from which the first bonobo specimens were collected in the 1920s. | Bonobo | Wikipedia | 366 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
Taxonomy
The bonobo was first recognised as a distinct taxon in 1928 by German anatomist Ernst Schwarz, based on a skull in the Tervuren Museum in Belgium which had previously been classified as a juvenile chimpanzee (Pan troglodytes). Schwarz published his findings in 1929, classifying the bonobo as a subspecies of chimpanzee, Pan satyrus paniscus. In 1933, American anatomist Harold Coolidge elevated it to species status. Major behavioural differences between bonobos and chimpanzees were first discussed in detail by Tratz and Heck in the early 1950s. Unaware of any taxonomic distinction with the common chimpanzee, American psychologist and primatologist Robert Yerkes had already noticed an unexpected major behavioural difference in the 1920s.
Bonobos and chimpanzees are the two species which make up the genus Pan, and are the closest living relatives to humans (Homo sapiens).
According to studies published in 2017 by researchers at The George Washington University, bonobos, along with common chimpanzees, split from the human line about 8 million years ago; moreover, bonobos split from the common chimpanzee line about 2 million years ago.
Nonetheless, the exact timing of the Pan–Homo last common ancestor is contentious, but DNA comparison suggests continual interbreeding between ancestral Pan and Homo groups, post-divergence, until about 4 million years ago. DNA evidence suggests the bonobo and common chimpanzee species diverged approximately 890,000–860,000 years ago following separation of these two populations possibly because of acidification and the spread of savannas at this time. Currently, these two species are separated by the Congo River, which had existed well before the divergence date, though ancestral Pan may have dispersed across the river using corridors which no longer exist. The first Pan fossils were reported in 2005 from the Middle Pleistocene (after the bonobo–chimpanzee split) of Kenya, alongside early Homo fossils.
According to A. Zihlman, bonobo body proportions closely resemble those of Australopithecus, leading evolutionary biologist Jeremy Griffith to suggest that bonobos may be a living example of our distant human ancestors. According to Australian anthropologists Gary Clark and Maciej Henneberg, human ancestors went through a bonobo-like phase featuring reduced aggression and associated anatomical changes, exemplified in Ardipithecus ramidus. | Bonobo | Wikipedia | 500 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
The first official publication of the sequencing and assembly of the bonobo genome was released in June 2012. The genome of a female bonobo from Leipzig Zoo was deposited with the International Nucleotide Sequence Database Collaboration (DDBJ/EMBL/GenBank) under the EMBL accession number AJFE01000000 after a previous analysis by the National Human Genome Research Institute confirmed that the bonobo genome is about 0.4% divergent from the chimpanzee genome.
Genetics and genomics
Relationships of bonobos to humans and other apes can be determined by comparing their genes or whole genomes. While the first bonobo genome was published in 2012, a high-quality reference genome became available only in 2021. The overall nucleotide divergence between chimpanzee and bonobo based on the latter is 0.421 ± 0.086% for autosomes and 0.311 ± 0.060% for the X chromosome. The reference genome predicts 22,366 full-length protein-coding genes and 9,066 noncoding genes, although cDNA sequencing confirmed only 20,478 protein-coding and 36,880 noncoding bonobo genes, similar to the number of genes annotated in the human genome. Overall, 206 and 1,576 protein-coding genes are part of gene families that contracted or expanded in the bonobo genome compared to the human genome, respectively, that is, these genes were lost or gained in the bonobo genome compared to humans.
Hybrids
Researchers have found that both central (Pan troglodytes troglodytes) and eastern chimpanzees (Pan troglodytes schweinfurthii) share more genetic material with bonobos than other chimpanzee subspecies. It is believed that genetic admixture has occurred at least two times within the past 550,000 years. In modern times hybridization between bonobos and chimpanzees in the wild is prevented as populations are allopatric and kept isolated on different sides of the Congo river.
Within captivity, hybrids between bonobos and chimpanzees have been recorded. Between 1990 and 1992, five pregnancies were conceived and studied between a male bonobo and two female chimpanzees. The two initial pregnancies were aborted because of environmental stressors. The following three pregnancies however led to the birth of three hybrid offspring. | Bonobo | Wikipedia | 500 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
A bonobo and chimpanzee hybrid called Tiby was also featured in the 2017 Swedish film The Square.
Description
The bonobo is commonly considered to be more gracile than the common chimpanzee. Although large male chimpanzees can exceed any bonobo in bulk and weight, the two species broadly overlap in body size. Adult female bonobos are somewhat smaller than adult males. Body mass ranges from with an average weight of in males against an average of in females. The total length of bonobos (from the nose to the rump while on all fours) is . Male bonobos average when standing upright, compared to in females. The bonobo's head is relatively smaller than that of the common chimpanzee with less prominent brow ridges above the eyes. It has a black face with pink lips, small ears, wide nostrils, and long hair on its head that forms a parting. Females have slightly more prominent breasts, in contrast to the flat breasts of other female apes, although not so prominent as those of humans. The bonobo also has a slim upper body, narrow shoulders, thin neck, and long legs when compared to the common chimpanzee.
Bonobos are both terrestrial and arboreal. Most ground locomotion is characterized by quadrupedal knuckle-walking. Bipedal walking has been recorded as less than 1% of terrestrial locomotion in the wild, a figure that decreased with habituation, while in captivity there is a wide variation. Bipedal walking in captivity, as a percentage of bipedal plus quadrupedal locomotion bouts, has been observed from 3.9% for spontaneous bouts to nearly 19% when abundant food is provided. These physical characteristics and its posture give the bonobo an appearance more closely resembling that of humans than the common chimpanzee does. The bonobo also has highly individuated facial features, as humans do, so that one individual may look significantly different from another, a characteristic adapted for visual facial recognition in social interaction.
Multivariate analysis has shown bonobos are more neotenized than the common chimpanzee, taking into account such features as the proportionately long torso length of the bonobo. Other researchers challenged this conclusion.
Behavior | Bonobo | Wikipedia | 464 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
Primatologist Frans de Waal states bonobos are capable of altruism, compassion, empathy, kindness, patience, and sensitivity, and described "bonobo society" as a "gynecocracy". Primatologists who have studied bonobos in the wild have documented a wide range of behaviors, including aggressive behavior and more cyclic sexual behavior similar to chimpanzees, even though bonobos show more sexual behavior in a greater variety of relationships. An analysis of female bonding among wild bonobos by Takeshi Furuichi stresses female sexuality and shows how female bonobos spend much more time in estrus than female chimpanzees.
Some primatologists have argued that de Waal's data reflect only the behavior of captive bonobos, suggesting that wild bonobos show levels of aggression closer to what is found among chimpanzees. De Waal has responded that the contrast in temperament between bonobos and chimpanzees observed in captivity is meaningful, because it controls for the influence of environment. The two species behave quite differently even if kept under identical conditions. A 2014 study also found bonobos to be less aggressive than chimpanzees, particularly eastern chimpanzees. The authors argued that the relative peacefulness of western chimpanzees and bonobos was primarily due to ecological factors. Bonobos warn each other of danger less efficiently than chimpanzees in the same situation.
Nonetheless, on 12 April 2024, biologists reported that bonobos behave more aggressively than thought earlier.
Social behavior
Bonobos are unusual among apes for their matriarchal social structure (extensive overlap between the male and female hierarchies leads some to refer to them as gender-balanced in their power structure). Bonobos do not have a defined territory and communities will travel over a wide range. Because of the nomadic nature of the females and evenly distributed food in their environment, males do not gain any obvious advantages by forming alliances with other males, or by defending a home range, as chimpanzees do. Female bonobos possess sharper canines than female chimpanzees, further fueling their status in the group. Although a male bonobo is dominant to a female in a dyadic interaction, depending on the community, socially-bonded females may be co-dominant with males or dominant over them, even to the extent that females can coerce reluctant males into mating with them. | Bonobo | Wikipedia | 502 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
At the top of the hierarchy is a coalition of high-ranking females and males typically headed by an old, experienced matriarch who acts as the decision-maker and leader of the group. Female bonobos typically earn their rank through experience, age, and ability to forge alliances with other females in their group, rather than physical intimidation, and top-ranking females will protect immigrant females from male harassment. While bonobos are often called matriarchal, and while every community is dominated by a female, some males will still obtain a high rank and act as coalitionary partners to the alpha female, often taking initiative in coordinating the groups movements. These males may outrank not only the other males in the group, but also many females. Certain males alert the group to any possible threats, protecting the group from predators such as pythons and leopards.
Aggressive encounters between males and females are rare, and males are tolerant of infants and juveniles. A male derives his status from the status of his mother. The mother–son bond often stays strong and continues throughout life. While social hierarchies do exist, and although the son of a high ranking female may outrank a lower female, rank plays a less prominent role than in other primate societies. Relationships between different communities are often positive and affiliative, and bonobos are not a territorial species. Bonobos will also share food with others, even unrelated strangers. Bonobos exhibit paedomorphism (retaining infantile physical characteristics and behaviours), which greatly inhibits aggression and enables unfamiliar bonobos to freely mingle and cooperate with each other.
Males engage in lengthy friendships with females and, in turn, female bonobos prefer to associate with and mate with males who are respectful and easygoing around them. Because female bonobos can use alliances to rebuff coercive and domineering males and select males at their own leisure, they show preference for males who are not aggressive towards them. Aging bonobos lose their playful streak and become noticeably more irritable in old age. Both sexes have a similar level of aggressiveness. Bonobos live in a male philopatric society where the females immigrate to new communities while males remain in their natal troop. However, it is not entirely unheard of for males to occasionally transfer into new groups. Additionally, females with powerful mothers may remain in their natal clan. | Bonobo | Wikipedia | 481 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
Alliances between males are poorly developed in most bonobo communities, while females will form alliances with each other and alliances between males and females occur, including multisex hunting parties. There is a confirmed case of a grown male bonobo adopting his orphaned infant brother. A mother bonobo will also support her grown son in conflicts with other males and help him secure better ties with other females, enhancing her chance of gaining grandchildren from him. She will even take measures such as physical intervention to prevent other males from breeding with certain females she wants her son to mate with. Although mothers play a role in aiding their sons, and the hierarchy among males is largely reflected by their mother's social status, some motherless males will still successfully dominate some males who do have mothers.
Female bonobos have also been observed fostering infants from outside their established community. Bonobos are not known to kill each other, and are generally less violent than chimpanzees, yet aggression still manifests itself in this species. Although female bonobos dominate males and selectively mate with males who do not exhibit aggression toward them, competition between the males themselves is intense and high-ranking males secure more matings than low-ranking ones. Indeed, the size difference between males and females is more pronounced in bonobos than it is in chimpanzees, as male bonobos do not form alliances and therefore have little incentive to hold back when fighting for access to females. Male bonobos are known to attack each other and inflict serious injuries such as missing digits, damaged eyes and torn ears. Some of these injuries may also occur when a male threatens the high ranking females and is injured by them, as the larger male is swarmed and outnumbered by a female mob.
Because of the promiscuous mating behavior of female bonobos, a male cannot be sure which offspring are his. As a result, the entirety of parental care in bonobos is assumed by the mothers. However, bonobos are not as promiscuous as chimpanzees and slightly polygamous tendencies occur, with high-ranking males enjoying greater reproductive success than low-ranking males. Unlike chimpanzees, where any male can coerce a female into mating with him, female bonobos enjoy greater sexual preferences and can rebuff undesirable males, an advantage of female-female bonding, and actively seek out higher-ranking males. | Bonobo | Wikipedia | 488 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
Bonobo party size tends to vary because the groups exhibit a fission–fusion pattern. A community of approximately 100 will split into small groups during the day while looking for food, and then will come back together to sleep. They sleep in nests that they construct in trees. Female bonobos more often than not secure feeding privileges and feed before males do, and although they are rarely successful in one-on-one confrontations with males, a female bonobo with several allies supporting her has extremely high success in monopolizing food sources. Different communities favour different prey. In some communities females exclusively hunt and have a preference for rodents, in others both sexes hunt, and will target monkeys. In captive settings, females exhibit extreme food-based aggression towards males, and forge coalitions against them to monopolize specific food items, often going as far as to mutilate any males who fail to heed their warning. In wild settings, however, female bonobos will quietly ask males for food if they had gotten it first, instead of forcibly confiscating it, suggesting sex-based hierarchy roles are less rigid than in captive colonies. Female bonobos are known to lead hunts on duikers and successfully defend their bounty from marauding males in the wild. They are more tolerant of younger males pestering them yet exhibit heightened aggression towards older males.
In a study published in November 2023, scientists reported, for the first time, evidence that groups of primates, particularly bonobos, are capable of cooperating with each other. Researchers observed unprecedented cooperation between two distinct bonobo groups in the Congo's Kokolopori Bonobo Reserve, Ekalakala and Kokoalongo, challenging traditional notions of ape societies. Over two years of observation, researchers witnessed 95 encounters between the groups. Contrary to expectations, these interactions resembled those within a single group. During these encounters, the bonobos engaged in behaviors such as grooming, food sharing, and collective defense against threats like snakes. Notably, the two groups, while displaying cooperative tendencies, maintained distinct identities, and there was no evidence of interbreeding or a blending of cultures. The cooperation observed was not arbitrary but evolved through individual bonds formed by exchanging favors and gifts. Some bonobos even formed alliances to target a third individual, demonstrating a nuanced social dynamic within the groups.
Sociosexual behaviour | Bonobo | Wikipedia | 478 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
Sexual activity generally plays a major role in bonobo society, being used as what some scientists perceive as a greeting, a means of forming social bonds, a means of conflict resolution, and postconflict reconciliation. Bonobos are the only non-human animal to have been observed engaging in tongue kissing. Bonobos and humans are the only primates to typically engage in face-to-face genital sex, although a pair of western gorillas has also been photographed in this position.
Bonobos do not form permanent monogamous sexual relationships with individual partners. They also do not seem to discriminate in their sexual behavior by sex or age, with the possible exception of abstaining from sexual activity between mothers and their adult sons. When bonobos come upon a new food source or feeding ground, the increased excitement will usually lead to communal sexual activity, presumably decreasing tension and encouraging peaceful feeding.
More often than the males, female bonobos engage in mutual genital-rubbing behavior, possibly to bond socially with each other, thus forming a female nucleus of bonobo society. The bonding among females enables them to dominate most of the males. Adolescent females often leave their native community to join another community. This migration mixes the bonobo gene pools, providing genetic diversity. Sexual bonding with other females establishes these new females as members of the group. | Bonobo | Wikipedia | 269 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
Bonobo clitorises are larger and more externalized than in most mammals; while the weight of a young adolescent female bonobo "is maybe half" that of a human teenager, she has a clitoris that is "three times bigger than the human equivalent, and visible enough to waggle unmistakably as she walks". In scientific literature, the female–female behavior of bonobos pressing vulvas together is often referred to as genito-genital (GG) rubbing. This sexual activity happens within the immediate female bonobo community and sometimes outside of it. Ethologist Jonathan Balcombe stated that female bonobos rub their clitorises together rapidly for ten to twenty seconds, and this behavior, "which may be repeated in rapid succession, is usually accompanied by grinding, shrieking, and clitoral engorgement"; he added that it is estimated that they engage in this practice "about once every two hours" on average. As bonobos occasionally copulate face-to-face, "evolutionary biologist Marlene Zuk has suggested that the position of the clitoris in bonobos and some other primates has evolved to maximize stimulation during sexual intercourse". The position of the clitoris may alternatively permit GG-rubbings, which has been hypothesized to function as a means for female bonobos to evaluate their intrasocial relationships. | Bonobo | Wikipedia | 280 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
Bonobo males engage in various forms of male–male genital behavior. The most common form of male–male mounting is similar to that of a heterosexual mounting: one of the males sits "passively on his back [with] the other male thrusting on him", with the penises rubbing together because of both males' erections. In another, rarer form of genital rubbing, two bonobo males hang from a tree limb face-to-face while penis fencing. This also may occur when two males rub their penises together while in face-to-face position. Another form of genital interaction (rump rubbing) often occurs to express reconciliation between two males after a conflict, when they stand back-to-back and rub their scrotal sacs together, but such behavior also occurs outside agonistic contexts: Kitamura (1989) observed rump–rump contacts between adult males following sexual solicitation behaviors similar to those between female bonobos prior to GG-rubbing. Takayoshi Kano observed similar practices among bonobos in the natural habitat. Tongue kissing, oral sex, and genital massaging have also been recorded among male bonobos.
Wild females give birth for the first time at 13 or 14 years of age. Bonobo reproductive rates are no higher than those of the common chimpanzee. However, female bonobo oestrus periods are longer. During oestrus, females undergo a swelling of the perineal tissue lasting 10 to 20 days. The gestation period is on average 240 days. Postpartum amenorrhea (absence of menstruation) lasts less than one year and a female may resume external signs of oestrus within a year of giving birth, though the female is probably not fertile at this point. Female bonobos carry and nurse their young for four years and give birth on average every 4.6 years. Compared to common chimpanzees, bonobo females resume the genital swelling cycle much sooner after giving birth, enabling them to rejoin the sexual activities of their society. Also, bonobo females which are sterile or too young to reproduce still engage in sexual activity. Mothers will help their sons get more matings from females in oestrus. | Bonobo | Wikipedia | 460 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
Adult male bonobos have sex with infants, although without penetration. Adult females also have sex with infants, but less frequently. Infants are not passive participants. They quite often initiate contacts with both adult males and females, as well as with peers. They have also been shown to be sexually active even in the absence of any stimulation or learning from adults.
Infanticide, while well documented in chimpanzees, is apparently absent in bonobo society. Although infanticide has not been directly observed, there have been documented cases of both female and male bonobos kidnapping infants, sometimes resulting in infants dying from dehydration. Although male bonobos have not yet been seen to practice infanticide, there is a documented incident in captivity involving a dominant female abducting an infant from a lower-ranking female, treating the infant roughly and denying it the chance to suckle. During the kidnapping, the infant's mother was clearly distressed and tried to retrieve her infant. Had the zookeepers not intervened, the infant almost certainly would have died from dehydration. This suggests female bonobos can have hostile rivalries with each other and a propensity to carry out infanticide.
The highly sexual nature of bonobo society and the fact that there is little competition over mates means that many males and females are mating with each other, in contrast to the one dominant male chimpanzee that fathers most of the offspring in a group. The strategy of bonobo females mating with many males may be a counterstrategy to infanticide because it confuses paternity. If male bonobos cannot distinguish their own offspring from others, the incentive for infanticide essentially disappears. This is a reproductive strategy that seems specific to bonobos; infanticide is observed in all other great apes except orangutans. Bonobos engage in sexual activity numerous times a day.
It is unknown how the bonobo avoids simian immunodeficiency virus (SIV) and its effects.
Peacefulness
Observations in the wild indicate that the males among the related common chimpanzee communities are hostile to males from outside the community. Parties of males 'patrol' for the neighboring males that might be traveling alone, and attack those single males, often killing them. This does not appear to be the behavior of bonobo males or females, which seem to prefer sexual contact over violent confrontation with outsiders. | Bonobo | Wikipedia | 481 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
While bonobos are more peaceful than chimpanzees, it is not true that they are unaggressive. In the wild, among males, bonobos are more aggressive than chimpanzees, having higher rates of aggressive acts, about three times as much. Although, male chimpanzees are more likely to be aggressive to a lethal degree than male bonobos which are more likely to engage in more frequent, yet less intense squabbling. There is also more female to male aggression with bonobos than there is with chimpanzees. Female bonobos are also more aggressive than female chimpanzees, in general. Both bonobos and chimpanzees exhibit physical aggression more than 100 times as often as humans do.
Although referred to as peaceful, bonobo aggression is not restricted to each other, and humans have also been attacked by bonobos, and suffered serious, albeit non-fatal, injuries.
Bonobos are far less violent than chimpanzees, though, as lethal aggression is essentially nonexistent among bonobos while being not infrequent among chimpanzees.
It has been hypothesized that bonobos are able to live a more peaceful lifestyle in part because of an abundance of nutritious vegetation in their natural habitat, allowing them to travel and forage in large parties.
Recent studies show that there are significant brain differences between bonobos and chimpanzees. Bonobos have more grey matter volume in the right anterior insula, right dorsal amygdala, hypothalamus, and right dorsomedial prefrontal cortex, all of which are regions assumed to be vital for feeling empathy, sensing distress in others and feeling anxiety. They also have a thick connection between the amygdala, an important area that can spark aggression, and the ventral anterior cingulate cortex, which has been shown to help control impulses in humans. This thicker connection may make them better at regulating their emotional impulses and behavior. | Bonobo | Wikipedia | 417 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
Bonobo society is dominated by females, and severing the lifelong alliance between mothers and their male offspring may make them vulnerable to female aggression. De Waal has warned of the danger of romanticizing bonobos: "All animals are competitive by nature and cooperative only under specific circumstances" and that "when first writing about their behaviour, I spoke of 'sex for peace' precisely because bonobos had plenty of conflicts. There would obviously be no need for peacemaking if they lived in perfect harmony."
Surbeck and Hohmann showed in 2008 that bonobos sometimes do hunt monkey species. Five incidents were observed in a group of bonobos in Salonga National Park, which seemed to reflect deliberate cooperative hunting. On three occasions, the hunt was successful, and infant monkeys were captured and eaten.
There is one inferred intraspecies killing in the wild, and a confirmed lethal attack in captivity. In both cases, the attackers were female and the victims were male.
Diet
The bonobo is an omnivorous frugivore; 57% of its diet is fruit, but this is supplemented with leaves, honey, eggs, meat from small vertebrates such as anomalures, flying squirrels and duikers, and invertebrates. The truffle species Hysterangium bonobo is eaten by bonobos. In some instances, bonobos have been shown to consume lower-order primates. Some claim bonobos have also been known to practise cannibalism in captivity, a claim disputed by others. However, at least one confirmed report of cannibalism in the wild of a dead infant was described in 2008. A 2016 paper reported two more instances of infant cannibalism, although it was not confirmed if infanticide was involved.
Cognitive comparisons to chimpanzees | Bonobo | Wikipedia | 369 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
In 2020, the first whole-genome comparison between chimpanzees and bonobos was published and showed genomic aspects that may underlie or have resulted from their divergence and behavioral differences, including selection for genes related to diet and hormones. A 2010 study found that "female bonobos displayed a larger range of tool use behaviours than males, a pattern previously described for chimpanzees but not for other great apes". This finding was affirmed by the results of another 2010 study which also found that "bonobos were more skilled at solving tasks related to theory of mind or an understanding of social causality, while chimpanzees were more skilled at tasks requiring the use of tools and an understanding of physical causality". Bonobos have been found to be more risk-averse compared to chimpanzees, preferring immediate rather than delayed rewards when it comes to foraging. Bonobos also have a weaker spatial memory compared to chimpanzees, with adult bonobos performing comparably to juvenile chimpanzees.
Similarity to humans
Bonobos are capable of passing the mirror-recognition test for self-awareness, as are all great apes. They communicate primarily through vocal means, although the meanings of their vocalizations are not currently known. However, most humans do understand their facial expressions and some of their natural hand gestures, such as their invitation to play. The communication system of wild bonobos includes a characteristic that was earlier only known in humans: bonobos use the same call to mean different things in different situations, and the other bonobos have to take the context into account when determining the meaning.
Two bonobos at the Great Ape Trust, Kanzi and Panbanisha, have been taught how to communicate using a keyboard labeled with lexigrams (geometric symbols) and they can respond to spoken sentences. Kanzi's vocabulary consists of more than 500 English words, and he has comprehension of around 3,000 spoken English words.
Kanzi is also known for learning by observing people trying to teach his mother; Kanzi started doing the tasks that his mother was taught just by watching, some of which his mother had failed to learn. Some, such as philosopher and bioethicist Peter Singer, argue that these results qualify them for "rights to survival and life"—rights which humans theoretically accord to all persons (See great ape personhood). | Bonobo | Wikipedia | 485 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
In the 1990s, Kanzi was taught to make and use simple stone tools. This resulted from a study undertaken by researchers Kathy Schick and Nicholas Toth, and later Gary Garufi. The researchers wanted to know if Kanzi possessed the cognitive and biomechanical abilities required to make and use stone tools. Though Kanzi was able to form flakes, he did not create them in the same way as humans, who hold the core in one hand and knap it with the other; Kanzi threw the cobble against a hard surface or against another cobble. This allowed him to produce a larger force to initiate a fracture as opposed to knapping it in his hands.
As in other great apes and humans, third party affiliation toward the victim—the affinitive contact made toward the recipient of an aggression by a group member other than the aggressor—is present in bonobos. A 2013 study found that both the affiliation spontaneously offered by a bystander to the victim and the affiliation requested by the victim (solicited affiliation) can reduce the probability of further aggression by group members on the victim (this fact supporting the Victim-Protection Hypothesis). Yet, only spontaneous affiliation reduced victim anxiety—measured via self-scratching rates—thus suggesting not only that non-solicited affiliation has a consolatory function but also that the spontaneous gesture—more than the protection itself—works in calming the distressed subject. The authors hypothesize that the victim may perceive the motivational autonomy of the bystander, who does not require an invitation to provide post-conflict affinitive contact. Moreover, spontaneous—but not solicited—third party affiliation was affected by the bond between consoler and victim (this supporting the Consolation Hypothesis). Importantly, spontaneous affiliation followed the empathic gradient described for humans, being mostly offered to kin, then friends, then acquaintances (these categories having been determined using affiliation rates between individuals). Hence, consolation in the bonobo may be an empathy-based phenomenon.
Instances in which bonobos have expressed joy have been reported. One study analyzed and recorded sounds made by human infants and bonobos when they were tickled. Although the bonobos' laugh was at a higher frequency, the laugh was found to follow a spectrographic pattern similar to that of human babies.
Distribution and habitat | Bonobo | Wikipedia | 479 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
Bonobos are found only south of the Congo River and north of the Kasai River (a tributary of the Congo), in the humid forests of the Democratic Republic of Congo. Ernst Schwarz's 1927 paper "Le Chimpanzé de la Rive Gauche du Congo", announcing his discovery, has been read as an association between the Parisian Left Bank and the left bank of the Congo River; the bohemian culture in Paris, and an unconventional ape in the Congo.
The ranges of bonobos and chimpanzees are separated by the Congo River, with bonobos living to its south and chimpanzees to the north.
Ecological role
In the Congo tropical rainforest, the very great majority of plants need animals to reproduce and disperse their seeds. Bonobos are the second largest frugivorous animals in this region, after elephants. It is estimated that during its life, each bonobo will ingest and disperse nine tons of seeds, from more than 91 species of lianas, grass, trees and shrubs. These seeds travel for about 24 hours in the bonobo digestive tract, which can transfer them over several kilometers (mean 1.3 km; max: 4.5 km), far from their parents, where they will be deposited intact in their feces. These dispersed seeds remain viable, germinating better and more quickly than unpassed seeds. For those seeds, diplochory with dung-beetles (Scarabaeidae) improves post-dispersal survival. | Bonobo | Wikipedia | 304 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
Certain plants such as Dialium may even be dependent on bonobos to activate the germination of their seeds, characterized by tegumentary dormancy. The first parameters of the effectiveness of seed dispersal by bonobos are present. Behavior of the bonobo could affect the population structure of plants whose seeds they disperse. The majority of these zoochorous plants cannot recruit without dispersal and the homogeneous spatial structure of the trees suggests a direct link with their dispersal agent. Few species could replace bonobos in terms of seed dispersal services, just as bonobos could not replace elephants. There is little functional redundancy between frugivorous mammals of the Congo, which face severe human hunting pressures and local extinction. The defaunation of the forests, leading to the empty forest syndrome, is critical in conservation biology. The disappearance of the bonobos, which disperse seeds of 40% of the tree species in these forests, or 11.6 million individual seeds during the life of each bonobo, would have consequences for the conservation of the Congo rainforest.
Conservation status
The IUCN Red List classifies bonobos as an endangered species, with conservative population estimates ranging from 29,500 to 50,000 individuals. Major threats to bonobo populations include habitat loss and hunting for bushmeat, the latter activity having increased dramatically during the first and second Congo Wars in the Democratic Republic of Congo, due to the presence of heavily armed militias (even in remote, "protected" areas such as Salonga National Park). This is part of a more general trend of ape extinction.
As the bonobos' habitat is shared with many people, the ultimate success of conservation efforts still relies on local and community involvement. The issue of parks versus people is salient in the Cuvette Centrale, within the bonobos' range. There is strong local, and broad-based Congolese, resistance to establishing national parks, as indigenous communities have previously been driven from their forest homes by the forming of parks. In Salonga National Park (the only national park in bonobo habitat), there is no local involvement, and surveys undertaken since 2000 indicate the bonobo, the African forest elephant, the okapi, and other rare species have been devastated by poachers and the thriving bushmeat trade. In contrast, areas do exist where the bonobo and ecological biodiversity still thrive without any established park borders, because of the indigenous beliefs/taboos against killing bonobos and other animals. | Bonobo | Wikipedia | 496 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
During the wars in the 1990s, researchers and international non-governmental organizations (NGOs) were driven out of the bonobo habitat. In 2002, the Bonobo Conservation Initiative initiated the Bonobo Peace Forest Project (supported by the Global Conservation Fund of Conservation International), in cooperation with national institutions, local NGOs, and local communities; the Peace Forest Project works with local communities to establish a linked constellation of community-based reserves managed by local and indigenous people. This model, implemented mainly through DRC organizations and local communities, has helped bring about agreements to protect over of the bonobo habitat. According to Amy Parish, the Bonobo Peace Forest "is going to be a model for conservation in the 21st century".
The port town of Basankusu is situated on the Lulonga River, at the confluence of the Lopori and Maringa Rivers, in the north of the country, making it well placed to receive and transport local goods to the cities of Mbandaka and Kinshasa. With Basankusu being the last port of substance before the wilderness of the Lopori Basin and the Lomako River—the bonobo heartland—conservation efforts for the bonobo use the town as a base.
In 1995, concern over declining numbers of bonobos in the wild led the Zoological Society of Milwaukee (ZSM), in Milwaukee, Wisconsin, with contributions from bonobo scientists around the world, to publish the Action Plan for Pan paniscus: A Report on Free Ranging Populations and Proposals for their Preservation. The Action Plan compiles population data on bonobos from 20 years of research conducted at various sites throughout the bonobo's range. The plan identifies priority actions for bonobo conservation and serves as a reference for developing conservation programs for researchers, government officials, and donor agencies. | Bonobo | Wikipedia | 365 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
Acting on Action Plan recommendations, the ZSM developed the Bonobo and Congo Biodiversity Initiative. This program includes habitat and rain-forest preservation, training for Congolese nationals and conservation institutions, wildlife population assessment and monitoring, and education. The ZSM has conducted regional surveys within the range of the bonobo in conjunction with training Congolese researchers in survey methodology and biodiversity monitoring. The ZSM's initial goal was to survey Salonga National Park to determine the conservation status of the bonobo within the park and to provide financial and technical assistance to strengthen park protection. As the project has developed, the ZSM has become more involved in helping the Congolese living in bonobo habitat. They have built schools, hired teachers, provided some medicines, and started an agriculture project to help the Congolese learn to grow crops and depend less on hunting wild animals.
With grants from the United Nations, USAID, the U.S. Embassy, the World Wildlife Fund, and many other groups and individuals, the ZSM also has been working to:
Survey the bonobo population and its habitat to find ways to help protect these apes
Develop antipoaching measures to help save apes, forest elephants, and other endangered animals in Congo's Salonga National Park, a UN World Heritage Site
Provide training, literacy education, agricultural techniques, schools, equipment, and jobs for Congolese living near bonobo habitats so that they will have a vested interest in protecting the great apes – the ZSM started an agriculture project to help the Congolese learn to grow crops and depend less on hunting wild animals.
Model small-scale conservation methods that can be used throughout Congo
Starting in 2003, the U.S. government allocated $54 million to the Congo Basin Forest Partnership. This significant investment has triggered the involvement of international NGOs to establish bases in the region and work to develop bonobo conservation programs. This initiative should improve the likelihood of bonobo survival, but its success still may depend upon building greater involvement and capability in local and indigenous communities.
The bonobo population is believed to have declined sharply in the last 30 years, though surveys have been hard to carry out in war-ravaged central Congo. Estimates range from 60,000 to fewer than 50,000 living, according to the World Wildlife Fund. | Bonobo | Wikipedia | 456 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
In addition, concerned parties have addressed the crisis on several science and ecological websites. Organizations such as the World Wide Fund for Nature, the African Wildlife Foundation, and others, are trying to focus attention on the extreme risk to the species. Some have suggested that a reserve be established in a more stable part of Africa, or on an island in a place such as Indonesia. Awareness is ever increasing, and even nonscientific or ecological sites have created various groups to collect donations to help with the conservation of this species.
Bonobos in human culture
World Bonobo Day is February 14 (Valentine's Day). This was established in 2017 by the African Wildlife Foundation. | Bonobo | Wikipedia | 134 | 45286 | https://en.wikipedia.org/wiki/Bonobo | Biology and health sciences | Primates | null |
In computer science, a thread of execution is the smallest sequence of programmed instructions that can be managed independently by a scheduler, which is typically a part of the operating system. In many cases, a thread is a component of a process.
The multiple threads of a given process may be executed concurrently (via multithreading capabilities), sharing resources such as memory, while different processes do not share these resources. In particular, the threads of a process share its executable code and the values of its dynamically allocated variables and non-thread-local global variables at any given time.
The implementation of threads and processes differs between operating systems.
History
Threads made an early appearance under the name of "tasks" in IBM's batch processing operating system, OS/360, in 1967. It provided users with three available configurations of the OS/360 control system, of which Multiprogramming with a Variable Number of Tasks (MVT) was one. Saltzer (1966) credits Victor A. Vyssotsky with the term "thread".
The use of threads in software applications became more common in the early 2000s as CPUs began to utilize multiple cores. Applications wishing to take advantage of multiple cores for performance advantages were required to employ concurrency to utilize the multiple cores.
Related concepts
Scheduling can be done at the kernel level or user level, and multitasking can be done preemptively or cooperatively. This yields a variety of related concepts.
Processes
At the kernel level, a process contains one or more kernel threads, which share the process's resources, such as memory and file handles – a process is a unit of resources, while a thread is a unit of scheduling and execution. Kernel scheduling is typically uniformly done preemptively or, less commonly, cooperatively. At the user level a process such as a runtime system can itself schedule multiple threads of execution. If these do not share data, as in Erlang, they are usually analogously called processes, while if they share data they are usually called (user) threads, particularly if preemptively scheduled. Cooperatively scheduled user threads are known as fibers; different processes may schedule user threads differently. User threads may be executed by kernel threads in various ways (one-to-one, many-to-one, many-to-many). The term "light-weight process" variously refers to user threads or to kernel mechanisms for scheduling user threads onto kernel threads. | Thread (computing) | Wikipedia | 498 | 45303 | https://en.wikipedia.org/wiki/Thread%20%28computing%29 | Technology | Operating systems | null |
A process is a "heavyweight" unit of kernel scheduling, as creating, destroying, and switching processes is relatively expensive. Processes own resources allocated by the operating system. Resources include memory (for both code and data), file handles, sockets, device handles, windows, and a process control block. Processes are isolated by process isolation, and do not share address spaces or file resources except through explicit methods such as inheriting file handles or shared memory segments, or mapping the same file in a shared way – see interprocess communication. Creating or destroying a process is relatively expensive, as resources must be acquired or released. Processes are typically preemptively multitasked, and process switching is relatively expensive, beyond basic cost of context switching, due to issues such as cache flushing (in particular, process switching changes virtual memory addressing, causing invalidation and thus flushing of an untagged translation lookaside buffer (TLB), notably on x86).
Kernel threads
A kernel thread is a "lightweight" unit of kernel scheduling. At least one kernel thread exists within each process. If multiple kernel threads exist within a process, then they share the same memory and file resources. Kernel threads are preemptively multitasked if the operating system's process scheduler is preemptive. Kernel threads do not own resources except for a stack, a copy of the registers including the program counter, and thread-local storage (if any), and are thus relatively cheap to create and destroy. Thread switching is also relatively cheap: it requires a context switch (saving and restoring registers and stack pointer), but does not change virtual memory and is thus cache-friendly (leaving TLB valid). The kernel can assign one or more software threads to each core in a CPU (it being able to assign itself multiple software threads depending on its support for multithreading), and can swap out threads that get blocked. However, kernel threads take much longer than user threads to be swapped.
User threads
Threads are sometimes implemented in userspace libraries, thus called user threads. The kernel is unaware of them, so they are managed and scheduled in userspace. Some implementations base their user threads on top of several kernel threads, to benefit from multi-processor machines (M:N model). User threads as implemented by virtual machines are also called green threads. | Thread (computing) | Wikipedia | 477 | 45303 | https://en.wikipedia.org/wiki/Thread%20%28computing%29 | Technology | Operating systems | null |
As user thread implementations are typically entirely in userspace, context switching between user threads within the same process is extremely efficient because it does not require any interaction with the kernel at all: a context switch can be performed by locally saving the CPU registers used by the currently executing user thread or fiber and then loading the registers required by the user thread or fiber to be executed. Since scheduling occurs in userspace, the scheduling policy can be more easily tailored to the requirements of the program's workload.
However, the use of blocking system calls in user threads (as opposed to kernel threads) can be problematic. If a user thread or a fiber performs a system call that blocks, the other user threads and fibers in the process are unable to run until the system call returns. A typical example of this problem is when performing I/O: most programs are written to perform I/O synchronously. When an I/O operation is initiated, a system call is made, and does not return until the I/O operation has been completed. In the intervening period, the entire process is "blocked" by the kernel and cannot run, which starves other user threads and fibers in the same process from executing.
A common solution to this problem (used, in particular, by many green threads implementations) is providing an I/O API that implements an interface that blocks the calling thread, rather than the entire process, by using non-blocking I/O internally, and scheduling another user thread or fiber while the I/O operation is in progress. Similar solutions can be provided for other blocking system calls. Alternatively, the program can be written to avoid the use of synchronous I/O or other blocking system calls (in particular, using non-blocking I/O, including lambda continuations and/or async/await primitives).
Fibers | Thread (computing) | Wikipedia | 376 | 45303 | https://en.wikipedia.org/wiki/Thread%20%28computing%29 | Technology | Operating systems | null |
Fibers are an even lighter unit of scheduling which are cooperatively scheduled: a running fiber must explicitly "yield" to allow another fiber to run, which makes their implementation much easier than kernel or user threads. A fiber can be scheduled to run in any thread in the same process. This permits applications to gain performance improvements by managing scheduling themselves, instead of relying on the kernel scheduler (which may not be tuned for the application). Some research implementations of the OpenMP parallel programming model implement their tasks through fibers. Closely related to fibers are coroutines, with the distinction being that coroutines are a language-level construct, while fibers are a system-level construct.
Threads vs processes
Threads differ from traditional multitasking operating-system processes in several ways:
processes are typically independent, while threads exist as subsets of a process
processes carry considerably more state information than threads, whereas multiple threads within a process share process state as well as memory and other resources
processes have separate address spaces, whereas threads share their address space
processes interact only through system-provided inter-process communication mechanisms
context switching between threads in the same process typically occurs faster than context switching between processes
Systems such as Windows NT and OS/2 are said to have cheap threads and expensive processes; in other operating systems there is not so great a difference except in the cost of an address-space switch, which on some architectures (notably x86) results in a translation lookaside buffer (TLB) flush.
Advantages and disadvantages of threads vs processes include:
Lower resource consumption of threads: using threads, an application can operate using fewer resources than it would need when using multiple processes.
Simplified sharing and communication of threads: unlike processes, which require a message passing or shared memory mechanism to perform inter-process communication (IPC), threads can communicate through data, code and files they already share.
Thread crashes a process: due to threads sharing the same address space, an illegal operation performed by a thread can crash the entire process; therefore, one misbehaving thread can disrupt the processing of all the other threads in the application.
Scheduling | Thread (computing) | Wikipedia | 427 | 45303 | https://en.wikipedia.org/wiki/Thread%20%28computing%29 | Technology | Operating systems | null |
Preemptive vs cooperative scheduling
Operating systems schedule threads either preemptively or cooperatively. Multi-user operating systems generally favor preemptive multithreading for its finer-grained control over execution time via context switching. However, preemptive scheduling may context-switch threads at moments unanticipated by programmers, thus causing lock convoy, priority inversion, or other side-effects. In contrast, cooperative multithreading relies on threads to relinquish control of execution, thus ensuring that threads run to completion. This can cause problems if a cooperatively multitasked thread blocks by waiting on a resource or if it starves other threads by not yielding control of execution during intensive computation.
Single- vs multi-processor systems
Until the early 2000s, most desktop computers had only one single-core CPU, with no support for hardware threads, although threads were still used on such computers because switching between threads was generally still quicker than full-process context switches. In 2002, Intel added support for simultaneous multithreading to the Pentium 4 processor, under the name hyper-threading; in 2005, they introduced the dual-core Pentium D processor and AMD introduced the dual-core Athlon 64 X2 processor.
Systems with a single processor generally implement multithreading by time slicing: the central processing unit (CPU) switches between different software threads. This context switching usually occurs frequently enough that users perceive the threads or tasks as running in parallel (for popular server/desktop operating systems, maximum time slice of a thread, when other threads are waiting, is often limited to 100–200ms). On a multiprocessor or multi-core system, multiple threads can execute in parallel, with every processor or core executing a separate thread simultaneously; on a processor or core with hardware threads, separate software threads can also be executed concurrently by separate hardware threads.
Threading models
1:1 (kernel-level threading)
Threads created by the user in a 1:1 correspondence with schedulable entities in the kernel are the simplest possible threading implementation. OS/2 and Win32 used this approach from the start, while on Linux the GNU C Library implements this approach (via the NPTL or older LinuxThreads). This approach is also used by Solaris, NetBSD, FreeBSD, macOS, and iOS. | Thread (computing) | Wikipedia | 484 | 45303 | https://en.wikipedia.org/wiki/Thread%20%28computing%29 | Technology | Operating systems | null |
M:1 (user-level threading)
An M:1 model implies that all application-level threads map to one kernel-level scheduled entity; the kernel has no knowledge of the application threads. With this approach, context switching can be done very quickly and, in addition, it can be implemented even on simple kernels which do not support threading. One of the major drawbacks, however, is that it cannot benefit from the hardware acceleration on multithreaded processors or multi-processor computers: there is never more than one thread being scheduled at the same time. For example: If one of the threads needs to execute an I/O request, the whole process is blocked and the threading advantage cannot be used. The GNU Portable Threads uses User-level threading, as does State Threads.
M:N (hybrid threading)
M:N maps some number of application threads onto some number of kernel entities, or "virtual processors." This is a compromise between kernel-level ("1:1") and user-level ("N:1") threading. In general, "M:N" threading systems are more complex to implement than either kernel or user threads, because changes to both kernel and user-space code are required. In the M:N implementation, the threading library is responsible for scheduling user threads on the available schedulable entities; this makes context switching of threads very fast, as it avoids system calls. However, this increases complexity and the likelihood of priority inversion, as well as suboptimal scheduling without extensive (and expensive) coordination between the userland scheduler and the kernel scheduler.
Hybrid implementation examples
Scheduler activations used by older versions of the NetBSD native POSIX threads library implementation (an M:N model as opposed to a 1:1 kernel or userspace implementation model)
Light-weight processes used by older versions of the Solaris operating system
Marcel from the PM2 project.
The OS for the Tera-Cray MTA-2
The Glasgow Haskell Compiler (GHC) for the language Haskell uses lightweight threads which are scheduled on operating system threads. | Thread (computing) | Wikipedia | 441 | 45303 | https://en.wikipedia.org/wiki/Thread%20%28computing%29 | Technology | Operating systems | null |
History of threading models in Unix systems
SunOS 4.x implemented light-weight processes or LWPs. NetBSD 2.x+, and DragonFly BSD implement LWPs as kernel threads (1:1 model). SunOS 5.2 through SunOS 5.8 as well as NetBSD 2 to NetBSD 4 implemented a two level model, multiplexing one or more user level threads on each kernel thread (M:N model). SunOS 5.9 and later, as well as NetBSD 5 eliminated user threads support, returning to a 1:1 model. FreeBSD 5 implemented M:N model. FreeBSD 6 supported both 1:1 and M:N, users could choose which one should be used with a given program using /etc/libmap.conf. Starting with FreeBSD 7, the 1:1 became the default. FreeBSD 8 no longer supports the M:N model.
Single-threaded vs multithreaded programs
In computer programming, single-threading is the processing of one instruction at a time. In the formal analysis of the variables' semantics and process state, the term single threading can be used differently to mean "backtracking within a single thread", which is common in the functional programming community.
Multithreading is mainly found in multitasking operating systems. Multithreading is a widespread programming and execution model that allows multiple threads to exist within the context of one process. These threads share the process's resources, but are able to execute independently. The threaded programming model provides developers with a useful abstraction of concurrent execution. Multithreading can also be applied to one process to enable parallel execution on a multiprocessing system.
Multithreading libraries tend to provide a function call to create a new thread, which takes a function as a parameter. A concurrent thread is then created which starts running the passed function and ends when the function returns. The thread libraries also offer data synchronization functions.
Threads and data synchronization | Thread (computing) | Wikipedia | 425 | 45303 | https://en.wikipedia.org/wiki/Thread%20%28computing%29 | Technology | Operating systems | null |
Threads in the same process share the same address space. This allows concurrently running code to couple tightly and conveniently exchange data without the overhead or complexity of an IPC. When shared between threads, however, even simple data structures become prone to race conditions if they require more than one CPU instruction to update: two threads may end up attempting to update the data structure at the same time and find it unexpectedly changing underfoot. Bugs caused by race conditions can be very difficult to reproduce and isolate.
To prevent this, threading application programming interfaces (APIs) offer synchronization primitives such as mutexes to lock data structures against concurrent access. On uniprocessor systems, a thread running into a locked mutex must sleep and hence trigger a context switch. On multi-processor systems, the thread may instead poll the mutex in a spinlock. Both of these may sap performance and force processors in symmetric multiprocessing (SMP) systems to contend for the memory bus, especially if the granularity of the locking is too fine.
Other synchronization APIs include condition variables, critical sections, semaphores, and monitors.
Thread pools
A popular programming pattern involving threads is that of thread pools where a set number of threads are created at startup that then wait for a task to be assigned. When a new task arrives, it wakes up, completes the task and goes back to waiting. This avoids the relatively expensive thread creation and destruction functions for every task performed and takes thread management out of the application developer's hand and leaves it to a library or the operating system that is better suited to optimize thread management.
Multithreaded programs vs single-threaded programs pros and cons | Thread (computing) | Wikipedia | 350 | 45303 | https://en.wikipedia.org/wiki/Thread%20%28computing%29 | Technology | Operating systems | null |
Multithreaded applications have the following advantages vs single-threaded ones:
Responsiveness: multithreading can allow an application to remain responsive to input. In a one-thread program, if the main execution thread blocks on a long-running task, the entire application can appear to freeze. By moving such long-running tasks to a worker thread that runs concurrently with the main execution thread, it is possible for the application to remain responsive to user input while executing tasks in the background. On the other hand, in most cases multithreading is not the only way to keep a program responsive, with non-blocking I/O and/or Unix signals being available for obtaining similar results.
Parallelization: applications looking to use multicore or multi-CPU systems can use multithreading to split data and tasks into parallel subtasks and let the underlying architecture manage how the threads run, either concurrently on one core or in parallel on multiple cores. GPU computing environments like CUDA and OpenCL use the multithreading model where dozens to hundreds of threads run in parallel across data on a large number of cores. This, in turn, enables better system utilization, and (provided that synchronization costs don't eat the benefits up), can provide faster program execution. | Thread (computing) | Wikipedia | 263 | 45303 | https://en.wikipedia.org/wiki/Thread%20%28computing%29 | Technology | Operating systems | null |
Multithreaded applications have the following drawbacks:
Synchronization complexity and related bugs: when using shared resources typical for threaded programs, the programmer must be careful to avoid race conditions and other non-intuitive behaviors. In order for data to be correctly manipulated, threads will often need to rendezvous in time in order to process the data in the correct order. Threads may also require mutually exclusive operations (often implemented using mutexes) to prevent common data from being read or overwritten in one thread while being modified by another. Careless use of such primitives can lead to deadlocks, livelocks or races over resources. As Edward A. Lee has written: "Although threads seem to be a small step from sequential computation, in fact, they represent a huge step. They discard the most essential and appealing properties of sequential computation: understandability, predictability, and determinism. Threads, as a model of computation, are wildly non-deterministic, and the job of the programmer becomes one of pruning that nondeterminism."
Being untestable. In general, multithreaded programs are non-deterministic, and as a result, are untestable. In other words, a multithreaded program can easily have bugs which never manifest on a test system, manifesting only in production. This can be alleviated by restricting inter-thread communications to certain well-defined patterns (such as message-passing).
Synchronization costs. As thread context switch on modern CPUs can cost up to 1 million CPU cycles, it makes writing efficient multithreading programs difficult. In particular, special attention has to be paid to avoid inter-thread synchronization from being too frequent.
Programming language support
Many programming languages support threading in some capacity. | Thread (computing) | Wikipedia | 370 | 45303 | https://en.wikipedia.org/wiki/Thread%20%28computing%29 | Technology | Operating systems | null |
IBM PL/I(F) included support for multithreading (called multitasking) as early as in the late 1960s, and this was continued in the Optimizing Compiler and later versions. The IBM Enterprise PL/I compiler introduced a new model "thread" API. Neither version was part of the PL/I standard.
Many implementations of C and C++ support threading, and provide access to the native threading APIs of the operating system. A standardized interface for thread implementation is POSIX Threads (Pthreads), which is a set of C-function library calls. OS vendors are free to implement the interface as desired, but the application developer should be able to use the same interface across multiple platforms. Most Unix platforms, including Linux, support Pthreads. Microsoft Windows has its own set of thread functions in the process.h interface for multithreading, like beginthread.
Some higher level (and usually cross-platform) programming languages, such as Java, Python, and .NET Framework languages, expose threading to developers while abstracting the platform specific differences in threading implementations in the runtime. Several other programming languages and language extensions also try to abstract the concept of concurrency and threading from the developer fully (Cilk, OpenMP, Message Passing Interface (MPI)). Some languages are designed for sequential parallelism instead (especially using GPUs), without requiring concurrency or threads (Ateji PX, CUDA).
A few interpreted programming languages have implementations (e.g., Ruby MRI for Ruby, CPython for Python) which support threading and concurrency but not parallel execution of threads, due to a global interpreter lock (GIL). The GIL is a mutual exclusion lock held by the interpreter that can prevent the interpreter from simultaneously interpreting the application's code on two or more threads at once. This effectively limits the parallelism on multiple core systems. It also limits performance for processor-bound threads (which require the processor), but doesn't effect I/O-bound or network-bound ones as much. Other implementations of interpreted programming languages, such as Tcl using the Thread extension, avoid the GIL limit by using an Apartment model where data and code must be explicitly "shared" between threads. In Tcl each thread has one or more interpreters. | Thread (computing) | Wikipedia | 479 | 45303 | https://en.wikipedia.org/wiki/Thread%20%28computing%29 | Technology | Operating systems | null |
In programming models such as CUDA designed for data parallel computation, an array of threads run the same code in parallel using only its ID to find its data in memory. In essence, the application must be designed so that each thread performs the same operation on different segments of memory so that they can operate in parallel and use the GPU architecture.
Hardware description languages such as Verilog have a different threading model that supports extremely large numbers of threads (for modeling hardware). | Thread (computing) | Wikipedia | 96 | 45303 | https://en.wikipedia.org/wiki/Thread%20%28computing%29 | Technology | Operating systems | null |
In game theory, the Nash equilibrium is the most commonly-used solution concept for non-cooperative games. A Nash equilibrium is a situation where no player could gain by changing their own strategy (holding all other players' strategies fixed). The idea of Nash equilibrium dates back to the time of Cournot, who in 1838 applied it to his model of competition in an oligopoly.
If each player has chosen a strategy an action plan based on what has happened so far in the game and no one can increase one's own expected payoff by changing one's strategy while the other players keep theirs unchanged, then the current set of strategy choices constitutes a Nash equilibrium.
If two players Alice and Bob choose strategies A and B, (A, B) is a Nash equilibrium if Alice has no other strategy available that does better than A at maximizing her payoff in response to Bob choosing B, and Bob has no other strategy available that does better than B at maximizing his payoff in response to Alice choosing A. In a game in which Carol and Dan are also players, (A, B, C, D) is a Nash equilibrium if A is Alice's best response to (B, C, D), B is Bob's best response to (A, C, D), and so forth.
Nash showed that there is a Nash equilibrium, possibly in mixed strategies, for every finite game.
Applications
Game theorists use Nash equilibrium to analyze the outcome of the strategic interaction of several decision makers. In a strategic interaction, the outcome for each decision-maker depends on the decisions of the others as well as their own. The simple insight underlying Nash's idea is that one cannot predict the choices of multiple decision makers if one analyzes those decisions in isolation. Instead, one must ask what each player would do taking into account what the player expects the others to do. Nash equilibrium requires that one's choices be consistent: no players wish to undo their decision given what the others are deciding. | Nash equilibrium | Wikipedia | 408 | 45337 | https://en.wikipedia.org/wiki/Nash%20equilibrium | Mathematics | Game theory | null |
The concept has been used to analyze hostile situations such as wars and arms races (see prisoner's dilemma), and also how conflict may be mitigated by repeated interaction (see tit-for-tat). It has also been used to study to what extent people with different preferences can cooperate (see battle of the sexes), and whether they will take risks to achieve a cooperative outcome (see stag hunt). It has been used to study the adoption of technical standards, and also the occurrence of bank runs and currency crises (see coordination game). Other applications include traffic flow (see Wardrop's principle), how to organize auctions (see auction theory), the outcome of efforts exerted by multiple parties in the education process, regulatory legislation such as environmental regulations (see tragedy of the commons), natural resource management, analysing strategies in marketing, penalty kicks in football (see matching pennies), robot navigation in crowds, energy systems, transportation systems, evacuation problems and wireless communications.
History
Nash equilibrium is named after American mathematician John Forbes Nash Jr. The same idea was used in a particular application in 1838 by Antoine Augustin Cournot in his theory of oligopoly. In Cournot's theory, each of several firms choose how much output to produce to maximize its profit. The best output for one firm depends on the outputs of the others. A Cournot equilibrium occurs when each firm's output maximizes its profits given the output of the other firms, which is a pure-strategy Nash equilibrium. Cournot also introduced the concept of best response dynamics in his analysis of the stability of equilibrium. Cournot did not use the idea in any other applications, however, or define it generally. | Nash equilibrium | Wikipedia | 358 | 45337 | https://en.wikipedia.org/wiki/Nash%20equilibrium | Mathematics | Game theory | null |
The modern concept of Nash equilibrium is instead defined in terms of mixed strategies, where players choose a probability distribution over possible pure strategies (which might put 100% of the probability on one pure strategy; such pure strategies are a subset of mixed strategies). The concept of a mixed-strategy equilibrium was introduced by John von Neumann and Oskar Morgenstern in their 1944 book The Theory of Games and Economic Behavior, but their analysis was restricted to the special case of zero-sum games. They showed that a mixed-strategy Nash equilibrium will exist for any zero-sum game with a finite set of actions. The contribution of Nash in his 1951 article "Non-Cooperative Games" was to define a mixed-strategy Nash equilibrium for any game with a finite set of actions and prove that at least one (mixed-strategy) Nash equilibrium must exist in such a game. The key to Nash's ability to prove existence far more generally than von Neumann lay in his definition of equilibrium. According to Nash, "an equilibrium point is an n-tuple such that each player's mixed strategy maximizes [their] payoff if the strategies of the others are held fixed. Thus each player's strategy is optimal against those of the others." Putting the problem in this framework allowed Nash to employ the Kakutani fixed-point theorem in his 1950 paper to prove existence of equilibria. His 1951 paper used the simpler Brouwer fixed-point theorem for the same purpose.
Game theorists have discovered that in some circumstances Nash equilibrium makes invalid predictions or fails to make a unique prediction. They have proposed many solution concepts ('refinements' of Nash equilibria) designed to rule out implausible Nash equilibria. One particularly important issue is that some Nash equilibria may be based on threats that are not 'credible'. In 1965 Reinhard Selten proposed subgame perfect equilibrium as a refinement that eliminates equilibria which depend on non-credible threats. Other extensions of the Nash equilibrium concept have addressed what happens if a game is repeated, or what happens if a game is played in the absence of complete information. However, subsequent refinements and extensions of Nash equilibrium share the main insight on which Nash's concept rests: the equilibrium is a set of strategies such that each player's strategy is optimal given the choices of the others.
Definitions | Nash equilibrium | Wikipedia | 485 | 45337 | https://en.wikipedia.org/wiki/Nash%20equilibrium | Mathematics | Game theory | null |
Nash equilibrium
A strategy profile is a set of strategies, one for each player. Informally, a strategy profile is a Nash equilibrium if no player can do better by unilaterally changing their strategy. To see what this means, imagine that each player is told the strategies of the others. Suppose then that each player asks themselves: "Knowing the strategies of the other players, and treating the strategies of the other players as set in stone, can I benefit by changing my strategy?"
For instance if a player prefers "Yes", then that set of strategies is not a Nash equilibrium. But if every player prefers not to switch (or is indifferent between switching and not) then the strategy profile is a Nash equilibrium. Thus, each strategy in a Nash equilibrium is a best response to the other players' strategies in that equilibrium.
Formally, let be the set of all possible strategies for player , where . Let be a strategy profile, a set consisting of one strategy for each player, where denotes the strategies of all the players except . Let be player is payoff as a function of the strategies. The strategy profile is a Nash equilibrium if
A game can have more than one Nash equilibrium. Even if the equilibrium is unique, it might be weak: a player might be indifferent among several strategies given the other players' choices. It is unique and called a strict Nash equilibrium if the inequality is strict so one strategy is the unique best response:
The strategy set can be different for different players, and its elements can be a variety of mathematical objects. Most simply, a player might choose between two strategies, e.g. Or the strategy set might be a finite set of conditional strategies responding to other players, e.g. Or it might be an infinite set, a continuum or unbounded, e.g. such that is a non-negative real number. Nash's existing proofs assume a finite strategy set, but the concept of Nash equilibrium does not require it.
Variants
Pure/mixed equilibrium
A game can have a pure-strategy or a mixed-strategy Nash equilibrium. In the latter, not every player always plays the same strategy. Instead, there is a probability distribution over different strategies.
Strict/non-strict equilibrium
Suppose that in the Nash equilibrium, each player asks themselves: "Knowing the strategies of the other players, and treating the strategies of the other players as set in stone, would I suffer a loss by changing my strategy?" | Nash equilibrium | Wikipedia | 493 | 45337 | https://en.wikipedia.org/wiki/Nash%20equilibrium | Mathematics | Game theory | null |
If every player's answer is "Yes", then the equilibrium is classified as a strict Nash equilibrium.
If instead, for some player, there is exact equality between the strategy in Nash equilibrium and some other strategy that gives exactly the same payout (i.e. the player is indifferent between switching and not), then the equilibrium is classified as a weak or non-strict Nash equilibrium.
Equilibria for coalitions
The Nash equilibrium defines stability only in terms of individual player deviations. In cooperative games such a concept is not convincing enough. Strong Nash equilibrium allows for deviations by every conceivable coalition. Formally, a strong Nash equilibrium is a Nash equilibrium in which no coalition, taking the actions of its complements as given, can cooperatively deviate in a way that benefits all of its members. However, the strong Nash concept is sometimes perceived as too "strong" in that the environment allows for unlimited private communication. In fact, strong Nash equilibrium has to be Pareto efficient. As a result of these requirements, strong Nash is too rare to be useful in many branches of game theory. However, in games such as elections with many more players than possible outcomes, it can be more common than a stable equilibrium.
A refined Nash equilibrium known as coalition-proof Nash equilibrium (CPNE) occurs when players cannot do better even if they are allowed to communicate and make "self-enforcing" agreement to deviate. Every correlated strategy supported by iterated strict dominance and on the Pareto frontier is a CPNE. Further, it is possible for a game to have a Nash equilibrium that is resilient against coalitions less than a specified size, k. CPNE is related to the theory of the core.
Existence
Nash's existence theorem
Nash proved that if mixed strategies (where a player chooses probabilities of using various pure strategies) are allowed, then every game with a finite number of players in which each player can choose from finitely many pure strategies has at least one Nash equilibrium, which might be a pure strategy for each player or might be a probability distribution over strategies for each player.
Nash equilibria need not exist if the set of choices is infinite and non-compact. For example: | Nash equilibrium | Wikipedia | 452 | 45337 | https://en.wikipedia.org/wiki/Nash%20equilibrium | Mathematics | Game theory | null |
A game where two players simultaneously name a number and the player naming the larger number wins does not have a NE, as the set of choices is not compact because it is unbounded.
Each of two players chooses a real number strictly less than 5 and the winner is whoever has the biggest number; no biggest number strictly less than 5 exists (if the number could equal 5, the Nash equilibrium would have both players choosing 5 and tying the game). Here, the set of choices is not compact because it is not closed.
However, a Nash equilibrium exists if the set of choices is compact with each player's payoff continuous in the strategies of all the players.
Rosen's existence theorem
Rosen extended Nash's existence theorem in several ways. He considers an n-player game, in which the strategy of each player i is a vector si in the Euclidean space Rmi. Denote m:=m1+...+mn; so a strategy-tuple is a vector in Rm. Part of the definition of a game is a subset S of Rm such that the strategy-tuple must be in S. This means that the actions of players may potentially be constrained based on actions of other players. A common special case of the model is when S is a Cartesian product of convex sets S1,...,Sn, such that the strategy of player i must be in Si. This represents the case that the actions of each player i are constrained independently of other players' actions. If the following conditions hold:
T is convex, closed and bounded;
Each payoff function ui is continuous in the strategies of all players, and concave in si for every fixed value of s−i.
Then a Nash equilibrium exists. The proof uses the Kakutani fixed-point theorem. Rosen also proves that, under certain technical conditions which include strict concavity, the equilibrium is unique.
Nash's result refers to the special case in which each Si is a simplex (representing all possible mixtures of pure strategies), and the payoff functions of all players are bilinear functions of the strategies.
Rationality
The Nash equilibrium may sometimes appear non-rational in a third-person perspective. This is because a Nash equilibrium is not necessarily Pareto optimal.
Nash equilibrium may also have non-rational consequences in sequential games because players may "threaten" each other with threats they would not actually carry out. For such games the subgame perfect Nash equilibrium may be more meaningful as a tool of analysis.
Examples | Nash equilibrium | Wikipedia | 511 | 45337 | https://en.wikipedia.org/wiki/Nash%20equilibrium | Mathematics | Game theory | null |
Coordination game
The coordination game is a classic two-player, two-strategy game, as shown in the example payoff matrix to the right. There are two pure-strategy equilibria, (A,A) with payoff 4 for each player and (B,B) with payoff 2 for each. The combination (B,B) is a Nash equilibrium because if either player unilaterally changes their strategy from B to A, their payoff will fall from 2 to 1.
A famous example of a coordination game is the stag hunt. Two players may choose to hunt a stag or a rabbit, the stag providing more meat (4 utility units, 2 for each player) than the rabbit (1 utility unit). The caveat is that the stag must be cooperatively hunted, so if one player attempts to hunt the stag, while the other hunts the rabbit, the stag hunter will totally fail, for a payoff of 0, whereas the rabbit hunter will succeed, for a payoff of 1. The game has two equilibria, (stag, stag) and (rabbit, rabbit), because a player's optimal strategy depends on their expectation on what the other player will do. If one hunter trusts that the other will hunt the stag, they should hunt the stag; however if they think the other will hunt the rabbit, they too will hunt the rabbit. This game is used as an analogy for social cooperation, since much of the benefit that people gain in society depends upon people cooperating and implicitly trusting one another to act in a manner corresponding with cooperation.
Driving on a road against an oncoming car, and having to choose either to swerve on the left or to swerve on the right of the road, is also a coordination game. For example, with payoffs 10 meaning no crash and 0 meaning a crash, the coordination game can be defined with the following payoff matrix: | Nash equilibrium | Wikipedia | 404 | 45337 | https://en.wikipedia.org/wiki/Nash%20equilibrium | Mathematics | Game theory | null |
In this case there are two pure-strategy Nash equilibria, when both choose to either drive on the left or on the right. If we admit mixed strategies (where a pure strategy is chosen at random, subject to some fixed probability), then there are three Nash equilibria for the same case: two we have seen from the pure-strategy form, where the probabilities are (0%, 100%) for player one, (0%, 100%) for player two; and (100%, 0%) for player one, (100%, 0%) for player two respectively. We add another where the probabilities for each player are (50%, 50%).
Network traffic
An application of Nash equilibria is in determining the expected flow of traffic in a network. Consider the graph on the right. If we assume that there are "cars" traveling from to , what is the expected distribution of traffic in the network?
This situation can be modeled as a "game", where every traveler has a choice of 3 strategies and where each strategy is a route from to (one of , , or ). The "payoff" of each strategy is the travel time of each route. In the graph on the right, a car travelling via experiences travel time of , where is the number of cars traveling on edge . Thus, payoffs for any given strategy depend on the choices of the other players, as is usual. However, the goal, in this case, is to minimize travel time, not maximize it. Equilibrium will occur when the time on all paths is exactly the same. When that happens, no single driver has any incentive to switch routes, since it can only add to their travel time. For the graph on the right, if, for example, 100 cars are travelling from to , then equilibrium will occur when 25 drivers travel via , 50 via , and 25 via . Every driver now has a total travel time of 3.75 (to see this, a total of 75 cars take the edge, and likewise, 75 cars take the edge). | Nash equilibrium | Wikipedia | 430 | 45337 | https://en.wikipedia.org/wiki/Nash%20equilibrium | Mathematics | Game theory | null |
Notice that this distribution is not, actually, socially optimal. If the 100 cars agreed that 50 travel via and the other 50 through , then travel time for any single car would actually be 3.5, which is less than 3.75. This is also the Nash equilibrium if the path between and is removed, which means that adding another possible route can decrease the efficiency of the system, a phenomenon known as Braess's paradox.
Competition game
This can be illustrated by a two-player game in which both players simultaneously choose an integer from 0 to 3 and they both win the smaller of the two numbers in points. In addition, if one player chooses a larger number than the other, then they have to give up two points to the other.
This game has a unique pure-strategy Nash equilibrium: both players choosing 0 (highlighted in light red). Any other strategy can be improved by a player switching their number to one less than that of the other player. In the adjacent table, if the game begins at the green square, it is in player 1's interest to move to the purple square and it is in player 2's interest to move to the blue square. Although it would not fit the definition of a competition game, if the game is modified so that the two players win the named amount if they both choose the same number, and otherwise win nothing, then there are 4 Nash equilibria: (0,0), (1,1), (2,2), and (3,3).
Nash equilibria in a payoff matrix
There is an easy numerical way to identify Nash equilibria on a payoff matrix. It is especially helpful in two-person games where players have more than two strategies. In this case formal analysis may become too long. This rule does not apply to the case where mixed (stochastic) strategies are of interest. The rule goes as follows: if the first payoff number, in the payoff pair of the cell, is the maximum of the column of the cell and if the second number is the maximum of the row of the cell then the cell represents a Nash equilibrium.
We can apply this rule to a 3×3 matrix: | Nash equilibrium | Wikipedia | 454 | 45337 | https://en.wikipedia.org/wiki/Nash%20equilibrium | Mathematics | Game theory | null |
Using the rule, we can very quickly (much faster than with formal analysis) see that the Nash equilibria cells are (B,A), (A,B), and (C,C). Indeed, for cell (B,A), 40 is the maximum of the first column and 25 is the maximum of the second row. For (A,B), 25 is the maximum of the second column and 40 is the maximum of the first row; the same applies for cell (C,C). For other cells, either one or both of the duplet members are not the maximum of the corresponding rows and columns.
This said, the actual mechanics of finding equilibrium cells is obvious: find the maximum of a column and check if the second member of the pair is the maximum of the row. If these conditions are met, the cell represents a Nash equilibrium. Check all columns this way to find all NE cells. An N×N matrix may have between 0 and N×N pure-strategy Nash equilibria.
Stability
The concept of stability, useful in the analysis of many kinds of equilibria, can also be applied to Nash equilibria.
A Nash equilibrium for a mixed-strategy game is stable if a small change (specifically, an infinitesimal change) in probabilities for one player leads to a situation where two conditions hold:
the player who did not change has no better strategy in the new circumstance
the player who did change is now playing with a strictly worse strategy.
If these cases are both met, then a player with the small change in their mixed strategy will return immediately to the Nash equilibrium. The equilibrium is said to be stable. If condition one does not hold then the equilibrium is unstable. If only condition one holds then there are likely to be an infinite number of optimal strategies for the player who changed. | Nash equilibrium | Wikipedia | 382 | 45337 | https://en.wikipedia.org/wiki/Nash%20equilibrium | Mathematics | Game theory | null |
In the "driving game" example above there are both stable and unstable equilibria. The equilibria involving mixed strategies with 100% probabilities are stable. If either player changes their probabilities slightly, they will be both at a disadvantage, and their opponent will have no reason to change their strategy in turn. The (50%,50%) equilibrium is unstable. If either player changes their probabilities (which would neither benefit or damage the expectation of the player who did the change, if the other player's mixed strategy is still (50%,50%)), then the other player immediately has a better strategy at either (0%, 100%) or (100%, 0%).
Stability is crucial in practical applications of Nash equilibria, since the mixed strategy of each player is not perfectly known, but has to be inferred from statistical distribution of their actions in the game. In this case unstable equilibria are very unlikely to arise in practice, since any minute change in the proportions of each strategy seen will lead to a change in strategy and the breakdown of the equilibrium.
Finally in the eighties, building with great depth on such ideas Mertens-stable equilibria were introduced as a solution concept. Mertens stable equilibria satisfy both forward induction and backward induction. In a game theory context stable equilibria now usually refer to Mertens stable equilibria.
Occurrence
If a game has a unique Nash equilibrium and is played among players under certain conditions, then the NE strategy set will be adopted. Sufficient conditions to guarantee that the Nash equilibrium is played are:
The players all will do their utmost to maximize their expected payoff as described by the game.
The players are flawless in execution.
The players have sufficient intelligence to deduce the solution.
The players know the planned equilibrium strategy of all of the other players.
The players believe that a deviation in their own strategy will not cause deviations by any other players.
There is common knowledge that all players meet these conditions, including this one. So, not only must each player know the other players meet the conditions, but also they must know that they all know that they meet them, and know that they know that they know that they meet them, and so on. | Nash equilibrium | Wikipedia | 470 | 45337 | https://en.wikipedia.org/wiki/Nash%20equilibrium | Mathematics | Game theory | null |
Where the conditions are not met
Examples of game theory problems in which these conditions are not met:
The first condition is not met if the game does not correctly describe the quantities a player wishes to maximize. In this case there is no particular reason for that player to adopt an equilibrium strategy. For instance, the prisoner's dilemma is not a dilemma if either player is happy to be jailed indefinitely.
Intentional or accidental imperfection in execution. For example, a computer capable of flawless logical play facing a second flawless computer will result in equilibrium. Introduction of imperfection will lead to its disruption either through loss to the player who makes the mistake, or through negation of the common knowledge criterion leading to possible victory for the player. (An example would be a player suddenly putting the car into reverse in the game of chicken, ensuring a no-loss no-win scenario).
In many cases, the third condition is not met because, even though the equilibrium must exist, it is unknown due to the complexity of the game, for instance in Chinese chess. Or, if known, it may not be known to all players, as when playing tic-tac-toe with a small child who desperately wants to win (meeting the other criteria).
The criterion of common knowledge may not be met even if all players do, in fact, meet all the other criteria. Players wrongly distrusting each other's rationality may adopt counter-strategies to expected irrational play on their opponents’ behalf. This is a major consideration in "chicken" or an arms race, for example.
Where the conditions are met
In his Ph.D. dissertation, John Nash proposed two interpretations of his equilibrium concept, with the objective of showing how equilibrium points can be connected with observable phenomenon.
This idea was formalized by R. Aumann and A. Brandenburger, 1995, Epistemic Conditions for Nash Equilibrium, Econometrica, 63, 1161-1180 who interpreted each player's mixed strategy as a conjecture about the behaviour of other players and have shown that if the game and the rationality of players is mutually known and these conjectures are commonly known, then the conjectures must be a Nash equilibrium (a common prior assumption is needed for this result in general, but not in the case of two players. In this case, the conjectures need only be mutually known).
A second interpretation, that Nash referred to by the mass action interpretation, is less demanding on players: | Nash equilibrium | Wikipedia | 500 | 45337 | https://en.wikipedia.org/wiki/Nash%20equilibrium | Mathematics | Game theory | null |
For a formal result along these lines, see Kuhn, H. and et al., 1996, "The Work of John Nash in Game Theory", Journal of Economic Theory, 69, 153–185.
Due to the limited conditions in which NE can actually be observed, they are rarely treated as a guide to day-to-day behaviour, or observed in practice in human negotiations. However, as a theoretical concept in economics and evolutionary biology, the NE has explanatory power. The payoff in economics is utility (or sometimes money), and in evolutionary biology is gene transmission; both are the fundamental bottom line of survival. Researchers who apply games theory in these fields claim that strategies failing to maximize these for whatever reason will be competed out of the market or environment, which are ascribed the ability to test all strategies. This conclusion is drawn from the "stability" theory above. In these situations the assumption that the strategy observed is actually a NE has often been borne out by research.
NE and non-credible threats
The Nash equilibrium is a superset of the subgame perfect Nash equilibrium. The subgame perfect equilibrium in addition to the Nash equilibrium requires that the strategy also is a Nash equilibrium in every subgame of that game. This eliminates all non-credible threats, that is, strategies that contain non-rational moves in order to make the counter-player change their strategy.
The image to the right shows a simple sequential game that illustrates the issue with subgame imperfect Nash equilibria. In this game player one chooses left(L) or right(R), which is followed by player two being called upon to be kind (K) or unkind (U) to player one, However, player two only stands to gain from being unkind if player one goes left. If player one goes right the rational player two would de facto be kind to her/him in that subgame. However, The non-credible threat of being unkind at 2(2) is still part of the blue (L, (U,U)) Nash equilibrium. Therefore, if rational behavior can be expected by both parties the subgame perfect Nash equilibrium may be a more meaningful solution concept when such dynamic inconsistencies arise.
Proof of existence | Nash equilibrium | Wikipedia | 457 | 45337 | https://en.wikipedia.org/wiki/Nash%20equilibrium | Mathematics | Game theory | null |
Proof using the Kakutani fixed-point theorem
Nash's original proof (in his thesis) used Brouwer's fixed-point theorem (e.g., see below for a variant). This section presents a simpler proof via the Kakutani fixed-point theorem, following Nash's 1950 paper (he credits David Gale with the observation that such a simplification is possible).
To prove the existence of a Nash equilibrium, let be the best response of player i to the strategies of all other players.
Here, , where , is a mixed-strategy profile in the set of all mixed strategies and is the payoff function for player i. Define a set-valued function such that . The existence of a Nash equilibrium is equivalent to having a fixed point.
Kakutani's fixed point theorem guarantees the existence of a fixed point if the following four conditions are satisfied.
is compact, convex, and nonempty.
is nonempty.
is upper hemicontinuous
is convex.
Condition 1. is satisfied from the fact that is a simplex and thus compact. Convexity follows from players' ability to mix strategies. is nonempty as long as players have strategies.
Condition 2. and 3. are satisfied by way of Berge's maximum theorem. Because is continuous and compact, is non-empty and upper hemicontinuous.
Condition 4. is satisfied as a result of mixed strategies. Suppose , then . i.e. if two strategies maximize payoffs, then a mix between the two strategies will yield the same payoff.
Therefore, there exists a fixed point in and a Nash equilibrium.
When Nash made this point to John von Neumann in 1949, von Neumann famously dismissed it with the words, "That's trivial, you know. That's just a fixed-point theorem." (See Nasar, 1998, p. 94.)
Alternate proof using the Brouwer fixed-point theorem
We have a game where is the number of players and is the action set for the players. All of the action sets are finite. Let denote the set of mixed strategies for the players. The finiteness of the s ensures the compactness of .
We can now define the gain functions. For a mixed strategy , we let the gain for player on action be
The gain function represents the benefit a player gets by unilaterally changing their strategy. We now define where
for . We see that
Next we define: | Nash equilibrium | Wikipedia | 501 | 45337 | https://en.wikipedia.org/wiki/Nash%20equilibrium | Mathematics | Game theory | null |
It is easy to see that each is a valid mixed strategy in . It is also easy to check that each is a continuous function of , and hence is a continuous function. As the cross product of a finite number of compact convex sets, is also compact and convex. Applying the Brouwer fixed point theorem to and we conclude that has a fixed point in , call it . We claim that is a Nash equilibrium in . For this purpose, it suffices to show that
This simply states that each player gains no benefit by unilaterally changing their strategy, which is exactly the necessary condition for a Nash equilibrium.
Now assume that the gains are not all zero. Therefore, and such that . Then
So let
Also we shall denote as the gain vector indexed by actions in . Since is the fixed point we have:
Since we have that is some positive scaling of the vector . Now we claim that
To see this, first if then this is true by definition of the gain function. Now assume that . By our previous statements we have that
and so the left term is zero, giving us that the entire expression is as needed.
So we finally have that
where the last inequality follows since is a non-zero vector. But this is a clear contradiction, so all the gains must indeed be zero. Therefore, is a Nash equilibrium for as needed.
Computing Nash equilibria
If a player A has a dominant strategy then there exists a Nash equilibrium in which A plays . In the case of two players A and B, there exists a Nash equilibrium in which A plays and B plays a best response to . If is a strictly dominant strategy, A plays in all Nash equilibria. If both A and B have strictly dominant strategies, there exists a unique Nash equilibrium in which each plays their strictly dominant strategy.
In games with mixed-strategy Nash equilibria, the probability of a player choosing any particular (so pure) strategy can be computed by assigning a variable to each strategy that represents a fixed probability for choosing that strategy. In order for a player to be willing to randomize, their expected payoff for each (pure) strategy should be the same. In addition, the sum of the probabilities for each strategy of a particular player should be 1. This creates a system of equations from which the probabilities of choosing each strategy can be derived.
Examples | Nash equilibrium | Wikipedia | 480 | 45337 | https://en.wikipedia.org/wiki/Nash%20equilibrium | Mathematics | Game theory | null |
In the matching pennies game, player A loses a point to B if A and B play the same strategy and wins a point from B if they play different strategies. To compute the mixed-strategy Nash equilibrium, assign A the probability of playing H and of playing T, and assign B the probability of playing H and of playing T.
Thus, a mixed-strategy Nash equilibrium in this game is for each player to randomly choose H or T with and .
Oddness of equilibrium points
In 1971, Robert Wilson came up with the "oddness theorem", which says that "almost all" finite games have a finite and odd number of Nash equilibria. In 1993, Harsanyi published an alternative proof of the result. "Almost all" here means that any game with an infinite or even number of equilibria is very special in the sense that if its payoffs were even slightly randomly perturbed, with probability one it would have an odd number of equilibria instead.
The prisoner's dilemma, for example, has one equilibrium, while the battle of the sexes has three—two pure and one mixed, and this remains true even if the payoffs change slightly. The free money game is an example of a "special" game with an even number of equilibria. In it, two players have to both vote "yes" rather than "no" to get a reward and the votes are simultaneous. There are two pure-strategy Nash equilibria, (yes, yes) and (no, no), and no mixed strategy equilibria, because the strategy "yes" weakly dominates "no". "Yes" is as good as "no" regardless of the other player's action, but if there is any chance the other player chooses "yes" then "yes" is the best reply. Under a small random perturbation of the payoffs, however, the probability that any two payoffs would remain tied, whether at 0 or some other number, is vanishingly small, and the game would have either one or three equilibria instead. | Nash equilibrium | Wikipedia | 433 | 45337 | https://en.wikipedia.org/wiki/Nash%20equilibrium | Mathematics | Game theory | null |
In computer science, control flow (or flow of control) is the order in which individual statements, instructions or function calls of an imperative program are executed or evaluated. The emphasis on explicit control flow distinguishes an imperative programming language from a declarative programming language.
Within an imperative programming language, a control flow statement is a statement that results in a choice being made as to which of two or more paths to follow. For non-strict functional languages, functions and language constructs exist to achieve the same result, but they are usually not termed control flow statements.
A set of statements is in turn generally structured as a block, which in addition to grouping, also defines a lexical scope.
Interrupts and signals are low-level mechanisms that can alter the flow of control in a way similar to a subroutine, but usually occur as a response to some external stimulus or event (that can occur asynchronously), rather than execution of an in-line control flow statement.
At the level of machine language or assembly language, control flow instructions usually work by altering the program counter. For some central processing units (CPUs), the only control flow instructions available are conditional or unconditional branch instructions, also termed jumps.
Categories
The kinds of control flow statements supported by different languages vary, but can be categorized by their effect:
Continuation at a different statement (unconditional branch or jump)
Executing a set of statements only if some condition is met (choice - i.e., conditional branch)
Executing a set of statements zero or more times, until some condition is met (i.e., loop - the same as conditional branch)
Executing a set of distant statements, after which the flow of control usually returns (subroutines, coroutines, and continuations)
Stopping the program, preventing any further execution (unconditional halt)
Primitives
Labels
A label is an explicit name or number assigned to a fixed position within the source code, and which may be referenced by control flow statements appearing elsewhere in the source code. A label marks a position within source code and has no other effect.
Line numbers are an alternative to a named label used in some languages (such as BASIC). They are whole numbers placed at the start of each line of text in the source code. Languages which use these often impose the constraint that the line numbers must increase in value in each following line, but may not require that they be consecutive. For example, in BASIC:
10 LET X = 3
20 PRINT X | Control flow | Wikipedia | 510 | 45459 | https://en.wikipedia.org/wiki/Control%20flow | Technology | Software development: General | null |
In other languages such as C and Ada, a label is an identifier, usually appearing at the start of a line and immediately followed by a colon. For example, in C:
Success: printf("The operation was successful.\n");
The language ALGOL 60 allowed both whole numbers and identifiers as labels (both linked by colons to the following statement), but few if any other ALGOL variants allowed whole numbers. Early Fortran compilers only allowed whole numbers as labels. Beginning with Fortran-90, alphanumeric labels have also been allowed.
Goto
The goto statement (a combination of the English words go and to, and pronounced accordingly) is the most basic form of unconditional transfer of control.
Although the keyword may either be in upper or lower case depending on the language, it is usually written as:
goto label
The effect of a goto statement is to cause the next statement to be executed to be the statement appearing at (or immediately after) the indicated label.
Goto statements have been considered harmful by many computer scientists, notably Dijkstra.
Subroutines
The terminology for subroutines varies; they may alternatively be known as routines, procedures, functions (especially if they return results) or methods (especially if they belong to classes or type classes).
In the 1950s, computer memories were very small by current standards so subroutines were used mainly to reduce program size. A piece of code was written once and then used many times from various other places in a program.
Today, subroutines are more often used to help make a program more structured, e.g., by isolating some algorithm or hiding some data access method. If many programmers are working on one program, subroutines are one kind of modularity that can help divide the work.
Sequence
In structured programming, the ordered sequencing of successive commands is considered one of the basic control structures, which is used as a building block for programs alongside iteration, recursion and choice.
Minimal structured control flow | Control flow | Wikipedia | 422 | 45459 | https://en.wikipedia.org/wiki/Control%20flow | Technology | Software development: General | null |
In May 1966, Böhm and Jacopini published an article in Communications of the ACM which showed that any program with gotos could be transformed into a goto-free form involving only choice (IF THEN ELSE) and loops (WHILE condition DO xxx), possibly with duplicated code and/or the addition of Boolean variables (true/false flags). Later authors showed that choice can be replaced by loops (and yet more Boolean variables).
That such minimalism is possible does not mean that it is necessarily desirable; computers theoretically need only one machine instruction (subtract one number from another and branch if the result is negative), but practical computers have dozens or even hundreds of machine instructions.
Other research showed that control structures with one entry and one exit were much easier to understand than any other form, mainly because they could be used anywhere as a statement without disrupting the control flow. In other words, they were composable. (Later developments, such as non-strict programming languages – and more recently, composable software transactions – have continued this strategy, making components of programs even more freely composable.)
Some academics took a purist approach to the Böhm–Jacopini result and argued that even instructions like break and return from the middle of loops are bad practice as they are not needed in the Böhm–Jacopini proof, and thus they advocated that all loops should have a single exit point. This purist approach is embodied in the language Pascal (designed in 1968–1969), which up to the mid-1990s was the preferred tool for teaching introductory programming in academia. The direct application of the Böhm–Jacopini theorem may result in additional local variables being introduced in the structured chart, and may also result in some code duplication. Pascal is affected by both of these problems and according to empirical studies cited by Eric S. Roberts, student programmers had difficulty formulating correct solutions in Pascal for several simple problems, including writing a function for searching an element in an array. A 1980 study by Henry Shapiro cited by Roberts found that using only the Pascal-provided control structures, the correct solution was given by only 20% of the subjects, while no subject wrote incorrect code for this problem if allowed to write a return from the middle of a loop. | Control flow | Wikipedia | 473 | 45459 | https://en.wikipedia.org/wiki/Control%20flow | Technology | Software development: General | null |
Control structures in practice
Most programming languages with control structures have an initial keyword which indicates the type of control structure involved. Languages then divide as to whether or not control structures have a final keyword.
No final keyword: ALGOL 60, C, C++, Go, Haskell, Java, Pascal, Perl, PHP, PL/I, Python, PowerShell. Such languages need some way of grouping statements together:
ALGOL 60 and Pascal: begin ... end
C, C++, Go, Java, Perl, PHP, and PowerShell: curly brackets { ... }
PL/I: DO ... END
Python: uses indent level (see Off-side rule)
Haskell: either indent level or curly brackets can be used, and they can be freely mixed
Lua: uses do ... end
Final keyword: Ada, APL, ALGOL 68, Modula-2, Fortran 77, Mythryl, Visual Basic. The forms of the final keyword vary:
Ada: final keyword is end + space + initial keyword e.g., if ... end if, loop ... end loop
APL: final keyword is :End optionally + initial keyword, e.g., :If ... :End or :If ... :EndIf, Select ... :End or :Select ... :EndSelect, however, if adding an end condition, the end keyword becomes :Until
ALGOL 68, Mythryl: initial keyword spelled backwards e.g., if ... fi, case ... esac
Fortran 77: final keyword is END + initial keyword e.g., IF ... ENDIF, DO ... ENDDO
Modula-2: same final keyword END for everything
Visual Basic: every control structure has its own keyword. If ... End If; For ... Next; Do ... Loop; While ... Wend
Choice
If-then-(else) statements | Control flow | Wikipedia | 432 | 45459 | https://en.wikipedia.org/wiki/Control%20flow | Technology | Software development: General | null |
Conditional expressions and conditional constructs are features of a programming language that perform different computations or actions depending on whether a programmer-specified Boolean condition evaluates to true or false.
IF..GOTO. A form found in unstructured languages, mimicking a typical machine code instruction, would jump to (GOTO) a label or line number when the condition was met.
IF..THEN..(ENDIF). Rather than being restricted to a jump, any simple statement, or nested block, could follow the THEN key keyword. This a structured form.
IF..THEN..ELSE..(ENDIF). As above, but with a second action to be performed if the condition is false. This is one of the most common forms, with many variations. Some require a terminal ENDIF, others do not. C and related languages do not require a terminal keyword, or a 'then', but do require parentheses around the condition.
Conditional statements can be and often are nested inside other conditional statements. Some languages allow ELSE and IF to be combined into ELSEIF, avoiding the need to have a series of ENDIF or other final statements at the end of a compound statement.
Less common variations include:
Some languages, such as early Fortran, have a three-way or arithmetic if, testing whether a numeric value is negative, zero, or positive.
Some languages have a functional form of an if statement, for instance Lisp's cond.
Some languages have an operator form of an if statement, such as C's ternary operator.
Perl supplements a C-style if with when and unless.
Smalltalk uses ifTrue and ifFalse messages to implement conditionals, rather than any fundamental language construct.
Case and switch statements
Switch statements (or case statements, or multiway branches) compare a given value with specified constants and take action according to the first constant to match. There is usually a provision for a default action ("else", "otherwise") to be taken if no match succeeds. Switch statements can allow compiler optimizations, such as lookup tables. In dynamic languages, the cases may not be limited to constant expressions, and might extend to pattern matching, as in the shell script example on the right, where the *) implements the default case as a glob matching any string. Case logic can also be implemented in functional form, as in SQL's decode statement. | Control flow | Wikipedia | 504 | 45459 | https://en.wikipedia.org/wiki/Control%20flow | Technology | Software development: General | null |
Loops
A loop is a sequence of statements which is specified once but which may be carried out several times in succession. The code "inside" the loop (the body of the loop, shown below as xxx) is obeyed a specified number of times, or once for each of a collection of items, or until some condition is met, or indefinitely. When one of those items is itself also a loop, it is called a "nested loop".
In functional programming languages, such as Haskell and Scheme, both recursive and iterative processes are expressed with tail recursive procedures instead of looping constructs that are syntactic.
Count-controlled loops
Most programming languages have constructions for repeating a loop a certain number of times.
In most cases counting can go downwards instead of upwards and step sizes other than 1 can be used.
In these examples, if N < 1 then the body of loop may execute once (with I having value 1) or not at all, depending on the programming language.
In many programming languages, only integers can be reliably used in a count-controlled loop. Floating-point numbers are represented imprecisely due to hardware constraints, so a loop such as
for X := 0.1 step 0.1 to 1.0 do
might be repeated 9 or 10 times, depending on rounding errors and/or the hardware and/or the compiler version. Furthermore, if the increment of X occurs by repeated addition, accumulated rounding errors may mean that the value of X in each iteration can differ quite significantly from the expected sequence 0.1, 0.2, 0.3, ..., 1.0.
Condition-controlled loops
Most programming languages have constructions for repeating a loop until some condition changes. Some variations test the condition at the start of the loop; others test it at the end. If the test is at the start, the body may be skipped completely; if it is at the end, the body is always executed at least once.
A control break is a value change detection method used within ordinary loops to trigger processing for groups of values. Values are monitored within the loop and a change diverts program flow to the handling of the group event associated with them.
DO UNTIL (End-of-File)
IF new-zipcode <> current-zipcode
display_tally(current-zipcode, zipcount)
current-zipcode = new-zipcode
zipcount = 0
ENDIF
zipcount++
LOOP
Collection-controlled loops | Control flow | Wikipedia | 512 | 45459 | https://en.wikipedia.org/wiki/Control%20flow | Technology | Software development: General | null |
Several programming languages (e.g., Ada, D, C++11, Smalltalk, PHP, Perl, Object Pascal, Java, C#, MATLAB, Visual Basic, Ruby, Python, JavaScript, Fortran 95 and later) have special constructs which allow implicit looping through all elements of an array, or all members of a set or collection.
someCollection do: [:eachElement |xxx].
for Item in Collection do begin xxx end;
foreach (item; myCollection) { xxx }
foreach someArray { xxx }
foreach ($someArray as $k => $v) { xxx }
Collection<String> coll; for (String s : coll) {}
foreach (string s in myStringCollection) { xxx }
someCollection | ForEach-Object { $_ }
forall ( index = first:last:step... )
Scala has for-expressions, which generalise collection-controlled loops, and also support other uses, such as asynchronous programming. Haskell has do-expressions and comprehensions, which together provide similar function to for-expressions in Scala.
General iteration
General iteration constructs such as C's for statement and Common Lisp's do form can be used to express any of the above sorts of loops, and others, such as looping over some number of collections in parallel. Where a more specific looping construct can be used, it is usually preferred over the general iteration construct, since it often makes the purpose of the expression clearer.
Infinite loops
Infinite loops are used to assure a program segment loops forever or until an exceptional condition arises, such as an error. For instance, an event-driven program (such as a server) should loop forever, handling events as they occur, only stopping when the process is terminated by an operator. | Control flow | Wikipedia | 395 | 45459 | https://en.wikipedia.org/wiki/Control%20flow | Technology | Software development: General | null |
Infinite loops can be implemented using other control flow constructs. Most commonly, in unstructured programming this is jump back up (goto), while in structured programming this is an indefinite loop (while loop) set to never end, either by omitting the condition or explicitly setting it to true, as while (true) .... Some languages have special constructs for infinite loops, typically by omitting the condition from an indefinite loop. Examples include Ada (loop ... end loop), Fortran (DO ... END DO), Go (for { ... }), and Ruby (loop do ... end).
Often, an infinite loop is unintentionally created by a programming error in a condition-controlled loop, wherein the loop condition uses variables that never change within the loop.
Continuation with next iteration
Sometimes within the body of a loop there is a desire to skip the remainder of the loop body and continue with the next iteration of the loop. Some languages provide a statement such as continue (most languages), skip, cycle (Fortran), or next (Perl and Ruby), which will do this. The effect is to prematurely terminate the innermost loop body and then resume as normal with the next iteration. If the iteration is the last one in the loop, the effect is to terminate the entire loop early.
Redo current iteration
Some languages, like Perl and Ruby, have a redo statement that restarts the current iteration from the start.
Restart loop
Ruby has a retry statement that restarts the entire loop from the initial iteration.
Early exit from loops
When using a count-controlled loop to search through a table, it might be desirable to stop searching as soon as the required item is found. Some programming languages provide a statement such as break (most languages), Exit (Visual Basic), or last (Perl), which effect is to terminate the current loop immediately, and transfer control to the statement immediately after that loop. Another term for early-exit loops is loop-and-a-half.
The following example is done in Ada which supports both early exit from loops and loops with test in the middle. Both features are very similar and comparing both code snippets will show the difference: early exit must be combined with an if statement while a condition in the middle is a self-contained construct.
with Ada.Text IO;
with Ada.Integer Text IO; | Control flow | Wikipedia | 502 | 45459 | https://en.wikipedia.org/wiki/Control%20flow | Technology | Software development: General | null |
procedure Print_Squares is
X : Integer;
begin
Read_Data : loop
Ada.Integer Text IO.Get(X);
exit Read_Data when X = 0;
Ada.Text IO.Put (X * X);
Ada.Text IO.New_Line;
end loop Read_Data;
end Print_Squares;
Python supports conditional execution of code depending on whether a loop was exited early (with a break statement) or not by using an else-clause with the loop. For example,
for n in set_of_numbers:
if isprime(n):
print("Set contains a prime number")
break
else:
print("Set did not contain any prime numbers")
The else clause in the above example is linked to the for statement, and not the inner if statement. Both Python's for and while loops support such an else clause, which is executed only if early exit of the loop has not occurred.
Some languages support breaking out of nested loops; in theory circles, these are called multi-level breaks. One common use example is searching a multi-dimensional table. This can be done either via multilevel breaks (break out of N levels), as in bash and PHP, or via labeled breaks (break out and continue at given label), as in Go, Java and Perl. Alternatives to multilevel breaks include single breaks, together with a state variable which is tested to break out another level; exceptions, which are caught at the level being broken out to; placing the nested loops in a function and using return to effect termination of the entire nested loop; or using a label and a goto statement. C does not include a multilevel break, and the usual alternative is to use a goto to implement a labeled break. Python does not have a multilevel break or continue – this was proposed in PEP 3136, and rejected on the basis that the added complexity was not worth the rare legitimate use. | Control flow | Wikipedia | 405 | 45459 | https://en.wikipedia.org/wiki/Control%20flow | Technology | Software development: General | null |
The notion of multi-level breaks is of some interest in theoretical computer science, because it gives rise to what is today called the Kosaraju hierarchy. In 1973 S. Rao Kosaraju refined the structured program theorem by proving that it is possible to avoid adding additional variables in structured programming, as long as arbitrary-depth, multi-level breaks from loops are allowed. Furthermore, Kosaraju proved that a strict hierarchy of programs exists: for every integer n, there exists a program containing a multi-level break of depth n that cannot be rewritten as a program with multi-level breaks of depth less than n without introducing added variables.
One can also return out of a subroutine executing the looped statements, breaking out of both the nested loop and the subroutine. There are other proposed control structures for multiple breaks, but these are generally implemented as exceptions instead.
In his 2004 textbook, David Watt uses Tennent's notion of sequencer to explain the similarity between multi-level breaks and return statements. Watt notes that a class of sequencers known as escape sequencers, defined as "sequencer that terminates execution of a textually enclosing command or procedure", encompasses both breaks from loops (including multi-level breaks) and return statements. As commonly implemented, however, return sequencers may also carry a (return) value, whereas the break sequencer as implemented in contemporary languages usually cannot.
Loop variants and invariants
Loop variants and loop invariants are used to express correctness of loops.
In practical terms, a loop variant is an integer expression which has an initial non-negative value. The variant's value must decrease during each loop iteration but must never become negative during the correct execution of the loop. Loop variants are used to guarantee that loops will terminate.
A loop invariant is an assertion which must be true before the first loop iteration and remain true after each iteration. This implies that when a loop terminates correctly, both the exit condition and the loop invariant are satisfied. Loop invariants are used to monitor specific properties of a loop during successive iterations.
Some programming languages, such as Eiffel contain native support for loop variants and invariants. In other cases, support is an add-on, such as the Java Modeling Language's specification for loop statements in Java. | Control flow | Wikipedia | 471 | 45459 | https://en.wikipedia.org/wiki/Control%20flow | Technology | Software development: General | null |
Loop sublanguage
Some Lisp dialects provide an extensive sublanguage for describing Loops. An early example can be found in Conversional Lisp of Interlisp. Common Lisp provides a Loop macro which implements such a sublanguage.
Loop system cross-reference table
while (true) does not count as an infinite loop for this purpose, because it is not a dedicated language structure.
C's for (init; test; increment) loop is a general loop construct, not specifically a counting one, although it is often used for that.
Deep breaks may be accomplished in APL, C, C++ and C# through the use of labels and gotos.
Iteration over objects was added in PHP 5.
A counting loop can be simulated by iterating over an incrementing list or generator, for instance, Python's range().
Deep breaks may be accomplished through the use of exception handling.
There is no special construct, since the while function can be used for this.
There is no special construct, but users can define general loop functions.
The C++11 standard introduced the range-based for. In the STL, there is a std::for_each template function which can iterate on STL containers and call a unary function for each element. The functionality also can be constructed as macro on these containers.
Count-controlled looping is effected by iteration across an integer interval; early exit by including an additional condition for exit.
Eiffel supports a reserved word retry, however it is used in exception handling, not loop control.
Requires Java Modeling Language (JML) behavioral interface specification language.
Requires loop variants to be integers; transfinite variants are not supported.
D supports infinite collections, and the ability to iterate over those collections. This does not require any special construct.
Deep breaks can be achieved using GO TO and procedures.
Common Lisp predates the concept of generic collection type.
Structured non-local control flow
Many programming languages, especially those favoring more dynamic styles of programming, offer constructs for non-local control flow. These cause the flow of execution to jump out of a given context and resume at some predeclared point. Conditions, exceptions and continuations are three common sorts of non-local control constructs; more exotic ones also exist, such as generators, coroutines and the async keyword. | Control flow | Wikipedia | 498 | 45459 | https://en.wikipedia.org/wiki/Control%20flow | Technology | Software development: General | null |
Conditions
The earliest Fortran compilers had statements for testing exceptional conditions. These included the IF ACCUMULATOR OVERFLOW, IF QUOTIENT OVERFLOW, and IF DIVIDE CHECK statements. In the interest of machine independence, they were not included in FORTRAN IV and the Fortran 66 Standard. However since Fortran 2003 it is possible to test for numerical issues via calls to functions in the IEEE_EXCEPTIONS module.
PL/I has some 22 standard conditions (e.g., ZERODIVIDE SUBSCRIPTRANGE ENDFILE) which can be raised and which can be intercepted by: ON condition action; Programmers can also define and use their own named conditions.
Like the unstructured if, only one statement can be specified so in many cases a GOTO is needed to decide where flow of control should resume.
Unfortunately, some implementations had a substantial overhead in both space and time (especially SUBSCRIPTRANGE), so many programmers tried to avoid using conditions.
Common Syntax examples:
ON condition GOTO label
Exceptions
Modern languages have a specialized structured construct for exception handling which does not rely on the use of GOTO or (multi-level) breaks or returns. For example, in C++ one can write:
try {
xxx1 // Somewhere in here
xxx2 // use: '''throw''' someValue;
xxx3
} catch (someClass& someId) { // catch value of someClass
actionForSomeClass
} catch (someType& anotherId) { // catch value of someType
actionForSomeType
} catch (...) { // catch anything not already caught
actionForAnythingElse
}
Any number and variety of catch clauses can be used above. If there is no catch matching a particular throw, control percolates back through subroutine calls and/or nested blocks until a matching catch is found or until the end of the main program is reached, at which point the program is forcibly stopped with a suitable error message. | Control flow | Wikipedia | 411 | 45459 | https://en.wikipedia.org/wiki/Control%20flow | Technology | Software development: General | null |
Via C++'s influence, catch is the keyword reserved for declaring a pattern-matching exception handler in other languages popular today, like Java or C#. Some other languages like Ada use the keyword exception to introduce an exception handler and then may even employ a different keyword (when in Ada) for the pattern matching. A few languages like AppleScript incorporate placeholders in the exception handler syntax to automatically extract several pieces of information when the exception occurs. This approach is exemplified below by the on error construct from AppleScript:
try
set myNumber to myNumber / 0
on error e number n from f to t partial result pr
if ( e = "Can't divide by zero" ) then display dialog "You must not do that"
end try
David Watt's 2004 textbook also analyzes exception handling in the framework of sequencers (introduced in this article in the section on early exits from loops). Watt notes that an abnormal situation, generally exemplified with arithmetic overflows or input/output failures like file not found, is a kind of error that "is detected in some low-level program unit, but [for which] a handler is more naturally located in a high-level program unit". For example, a program might contain several calls to read files, but the action to perform when a file is not found depends on the meaning (purpose) of the file in question to the program and thus a handling routine for this abnormal situation cannot be located in low-level system code. Watts further notes that introducing status flags testing in the caller, as single-exit structured programming or even (multi-exit) return sequencers would entail, results in a situation where "the application code tends to get cluttered by tests of status flags" and that "the programmer might forgetfully or lazily omit to test a status flag. In fact, abnormal situations represented by status flags are by default ignored!" Watt notes that in contrast to status flags testing, exceptions have the opposite default behavior, causing the program to terminate unless the program deals with the exception explicitly in some way, possibly by adding explicit code to ignore it. Based on these arguments, Watt concludes that jump sequencers or escape sequencers are less suitable as a dedicated exception sequencer with the semantics discussed above. | Control flow | Wikipedia | 467 | 45459 | https://en.wikipedia.org/wiki/Control%20flow | Technology | Software development: General | null |
In Object Pascal, D, Java, C#, and Python a finally clause can be added to the try construct. No matter how control leaves the try the code inside the finally clause is guaranteed to execute. This is useful when writing code that must relinquish an expensive resource (such as an opened file or a database connection) when finished processing:
FileStream stm = null; // C# example
try
{
stm = new FileStream("logfile.txt", FileMode.Create);
return ProcessStuff(stm); // may throw an exception
}
finally
{
if (stm != null)
stm.Close();
}
Since this pattern is fairly common, C# has a special syntax:
using (var stm = new FileStream("logfile.txt", FileMode.Create))
{
return ProcessStuff(stm); // may throw an exception
}
Upon leaving the using-block, the compiler guarantees that the stm object is released, effectively binding the variable to the file stream while abstracting from the side effects of initializing and releasing the file. Python's with statement and Ruby's block argument to File.open are used to similar effect.
All the languages mentioned above define standard exceptions and the circumstances under which they are thrown. Users can throw exceptions of their own; C++ allows users to throw and catch almost any type, including basic types like int, whereas other languages like Java are less permissive.
Continuations
Async
C# 5.0 introduced the async keyword for supporting asynchronous I/O in a "direct style".
Generators
Generators, also known as semicoroutines, allow control to be yielded to a consumer method temporarily, typically using a keyword (yield description) . Like the async keyword, this supports programming in a "direct style".
Coroutines
Coroutines are functions that can yield control to each other - a form of co-operative multitasking without threads.
Coroutines can be implemented as a library if the programming language provides either continuations or generators - so the distinction between coroutines and generators in practice is a technical detail.
Non-local control flow cross reference | Control flow | Wikipedia | 477 | 45459 | https://en.wikipedia.org/wiki/Control%20flow | Technology | Software development: General | null |
Proposed control structures
In a spoof Datamation article in 1973, R. Lawrence Clark suggested that the GOTO statement could be replaced by the COMEFROM statement, and provides some entertaining examples. COMEFROM was implemented in one esoteric programming language named INTERCAL.
Donald Knuth's 1974 article "Structured Programming with go to Statements", identifies two situations which were not covered by the control structures listed above, and gave examples of control structures which could handle these situations. Despite their utility, these constructs have not yet found their way into mainstream programming languages.
Loop with test in the middle
The following was proposed by Dahl in 1972:
loop loop
xxx1 read(char);
while test; while not atEndOfFile;
xxx2 write(char);
repeat; repeat;
If xxx1 is omitted, we get a loop with the test at the top (a traditional while loop). If xxx2 is omitted, we get a loop with the test at the bottom, equivalent to a do while loop in many languages. If while is omitted, we get an infinite loop. The construction here can be thought of as a do loop with the while check in the middle. Hence this single construction can replace several constructions in most programming languages.
Languages lacking this construct generally emulate it using an equivalent infinite-loop-with-break idiom:
while (true) {
xxx1
if (not test)
break
xxx2
}
A possible variant is to allow more than one while test; within the loop, but the use of exitwhen (see next section) appears to cover this case better.
In Ada, the above loop construct (loop-while-repeat) can be represented using a standard infinite loop (loop - end loop) that has an exit when clause in the middle (not to be confused with the exitwhen statement in the following section).
with Ada.Text_IO;
with Ada.Integer_Text_IO;
procedure Print_Squares is
X : Integer;
begin
Read_Data : loop
Ada.Integer_Text_IO.Get(X);
exit Read_Data when X = 0;
Ada.Text IO.Put (X * X);
Ada.Text IO.New_Line;
end loop Read_Data;
end Print_Squares;
Naming a loop (like Read_Data in this example) is optional but permits leaving the outer loop of several nested loops. | Control flow | Wikipedia | 495 | 45459 | https://en.wikipedia.org/wiki/Control%20flow | Technology | Software development: General | null |
Multiple early exit/exit from nested loops
This construct was proposed by Zahn in 1974. A modified version is presented here.
exitwhen EventA or EventB or EventC;
xxx
exits
EventA: actionA
EventB: actionB
EventC: actionC
endexit;
exitwhen is used to specify the events which may occur within xxx,
their occurrence is indicated by using the name of the event as a statement. When some event does occur, the relevant action is carried out, and then control passes just after . This construction provides a very clear separation between determining that some situation applies, and the action to be taken for that situation.
exitwhen is conceptually similar to exception handling, and exceptions or similar constructs are used for this purpose in many languages.
The following simple example involves searching a two-dimensional table for a particular item.
exitwhen found or missing;
for I := 1 to N do
for J := 1 to M do
if table[I,J] = target then found;
missing;
exits
found: print ("item is in table");
missing: print ("item is not in table");
endexit;
Security
One way to attack a piece of software is to redirect the flow of execution of a program. A variety of control-flow integrity techniques, including stack canaries, buffer overflow protection, shadow stacks, and vtable pointer verification, are used to defend against these attacks. | Control flow | Wikipedia | 302 | 45459 | https://en.wikipedia.org/wiki/Control%20flow | Technology | Software development: General | null |
Coelacanths ( ) (order Coelacanthiformes) are an ancient group of lobe-finned fish (Sarcopterygii) in the class Actinistia. As sarcopterygians, they are more closely related to lungfish and tetrapods (which includes amphibians, reptiles, birds and mammals) than to ray-finned fish.
Well-represented in both freshwater and marine fossils since the Devonian, they are now represented by only two extant marine species in the genus Latimeria: the West Indian Ocean coelacanth (Latimeria chalumnae), primarily found near the Comoro Islands off the east coast of Africa, and the Indonesian coelacanth (Latimeria menadoensis). The name coelacanth originates from the Permian genus Coelacanthus, which was the first scientifically named coelacanth.
The oldest known coelacanth fossils date back more than 410million years. Coelacanths were thought to have become extinct in the Late Cretaceous, around 66million years ago, but were discovered living off the coast of South Africa in 1938.
The coelacanth was long considered a "living fossil" because scientists thought it was the sole remaining member of a taxon otherwise known only from fossils, with no close relations alive, and that it evolved into roughly its current form approximately 400million years ago. However, several more recent studies have shown that coelacanth body shapes are much more diverse than previously thought.
Etymology
The word Coelacanth is an adaptation of the Modern Latin ('hollow spine'), from the Greek (, 'hollow') and (, 'spine'), referring to the hollow caudal fin rays of the first fossil specimen described and named by Louis Agassiz in 1839, belonging to the genus Coelacanthus. The genus name Latimeria commemorates Marjorie Courtenay-Latimer, who discovered the first specimen.
Discovery | Coelacanth | Wikipedia | 411 | 45503 | https://en.wikipedia.org/wiki/Coelacanth | Biology and health sciences | Fishes | null |
The earliest fossils of coelacanths were discovered in the 19th century. Coelacanths, which are related to lungfishes and tetrapods, were believed to have become extinct at the end of the Cretaceous period. More closely related to tetrapods than to the ray-finned fish, coelacanths were considered transitional species between fish and tetrapods. On 22 December 1938, the first Latimeria specimen was found off the east coast of South Africa, off the Chalumna River (now Tyolomnqa). Museum curator Marjorie Courtenay-Latimer discovered the fish among the catch of a local fisherman. Courtenay-Latimer contacted a Rhodes University ichthyologist, J. L. B. Smith, sending him drawings of the fish, and he confirmed the fish's importance with a famous cable: "Most Important Preserve Skeleton and Gills = Fish Described."
Its discovery 66 million years after its supposed extinction makes the coelacanth the best-known example of a Lazarus taxon, an evolutionary line that seems to have disappeared from the fossil record only to reappear much later. Since 1938, West Indian Ocean coelacanth have been found in the Comoros, Kenya, Tanzania, Mozambique, Madagascar, in iSimangaliso Wetland Park, and off the South Coast of Kwazulu-Natal in South Africa.
The Comoro Islands specimen was discovered in December 1952. Between 1938 and 1975, 84 specimens were caught and recorded.
The second extant species, the Indonesian coelacanth, was described from Manado, North Sulawesi, Indonesia, in 1999 by Pouyaud et al. based on a specimen discovered by Mark V. Erdmann in 1998 and deposited at the Indonesian Institute of Sciences (LIPI). Erdmann and his wife Arnaz Mehta first encountered a specimen at a local market in September 1997, but took only a few photographs of the first specimen of this species before it was sold. After confirming that it was a unique discovery, Erdmann returned to Sulawesi in November 1997 to interview fishermen and look for further examples. A second specimen was caught by a fisherman in July 1998 and was then handed to Erdmann.
Description | Coelacanth | Wikipedia | 452 | 45503 | https://en.wikipedia.org/wiki/Coelacanth | Biology and health sciences | Fishes | null |
Latimeria chalumnae and L. menadoensis are the only two known living coelacanth species. Coelacanths are large, plump, lobe-finned fish that can grow to more than and weigh around . They are estimated to live up to 100 years, based on analysis of annual growth marks on scales, and reach maturity around the age of 55; the oldest known specimen was 84 years old at the time of its capture in 1960.
Even though their estimated lifetime is similar to humans, gestation can last 5 years, which is 1.5 years more than the deep-sea frilled shark, the previous record holder.
They are nocturnal piscivorous drift-hunters.
The body is covered in ctenoid elasmoid scales that act as armor. Coelacanths have eight fins – two dorsal fins, two pectoral fins, two pelvic fins, one anal fin and one caudal fin. The tail is very nearly equally proportioned and is split by a terminal tuft of fin rays that make up its caudal lobe. The eyes of the coelacanth are very large, while the mouth is very small. The eye is acclimatized to seeing in poor light by rods that absorb mostly short wavelengths. Coelacanth vision has evolved to a mainly blue-shifted color capacity. Pseudomaxillary folds surround the mouth and replace the maxilla, a structure absent in coelacanths. Two nostrils, along with four other external openings, appear between the premaxilla and lateral rostral bones. The nasal sacs resemble those of many other fish and do not contain an internal nostril. The coelacanth's rostral organ, contained within the ethmoid region of the braincase, has three unguarded openings into the environment and is used as a part of the coelacanth's laterosensory system. The coelacanth's auditory reception is mediated by its inner ear, which is very similar to that of tetrapods and is classified as being a basilar papilla. | Coelacanth | Wikipedia | 436 | 45503 | https://en.wikipedia.org/wiki/Coelacanth | Biology and health sciences | Fishes | null |
Coelacanths are a part of the clade Sarcopterygii, or the lobe-finned fishes. They share membership in this clade with lungfish and tetrapods. Externally, several characteristics distinguish coelacanths from other lobe-finned fish. They possess a three-lobed caudal fin, also called a trilobate fin or a diphycercal tail. A secondary tail extending past the primary tail separates the upper and lower halves of the coelacanth. Ctenoid elasmoid scales act as thick armor to protect the coelacanth's exterior. Several internal traits also aid in differentiating coelacanths from other lobe-finned fish. At the back of the skull, the coelacanth possesses a hinge, the intracranial joint, which allows it to open its mouth extremely wide. Coelacanths also retain an oil-filled notochord, a hollow, pressurized tube which is replaced by a vertebral column early in embryonic development in most other vertebrates. The coelacanth's heart is shaped differently from that of most modern fish, with its chambers arranged in a straight tube. The coelacanth's braincase is 98.5% filled with fat; only 1.5% of the braincase contains brain tissue. The cheeks of the coelacanth are unique because the opercular bone is very small and holds a large soft-tissue opercular flap. A spiracular chamber is present, but the spiracle is closed and never opens during development. Also unique to extant coelacanths is the presence of a "fatty lung" or a fat-filled single-lobed vestigial lung, homologous to other fishes' swim bladders. The parallel development of a fatty organ for buoyancy control suggests a unique specialization for deep-water habitats. There are small and hard but flexible plates around the vestigial lung in adult specimens, though not around the fatty organ. The plates most likely had a regulation function for the volume of the lung. Due to the size of the fatty organ, researchers assume that it is responsible for the kidney's unusual relocation. The two kidneys, which are fused into one, are located ventrally within the abdominal cavity, posterior to the cloaca.
DNA
In 2013, a research group published the genome sequence of the coelacanth in the scientific journal Nature. | Coelacanth | Wikipedia | 509 | 45503 | https://en.wikipedia.org/wiki/Coelacanth | Biology and health sciences | Fishes | null |
Due to their lobed fins and other features, it was once hypothesized that the coelacanth might be the youngest diverging non-tetrapod sarcopterygian. But after sequencing the full genome of the coelacanth, it was discovered that the lungfish instead is more closely related to tetrapods. Coelacanths and rhipidistians (the concestor of lungfish and tetrapods) had already diverged from each other before the lungfish made the transition to land.
Another important discovery made from the genome sequencing is that the coelacanths are still evolving today. While phenotypic similarity between extant and extinct coelacanths suggests there is limited evolutionary pressure on these organisms to undergo morphological divergence, they are undergoing measurable genetic divergence. Despite prior studies showing that protein coding regions are undergoing evolution at a substitution rate much lower than other sarcopterygians (consistent with phenotypic stasis observed between extant and fossil members of the taxa), the non-coding regions subject to higher transposable element activity show marked divergence even between the two extant coelacanth species. This has been facilitated in part by a coelacanth-specific endogenous retrovirus of the Epsilon retrovirus family.
Taxonomy
Cladogram showing the relationships of coelacanth genera after Torino, Soto and Perea, 2021.
Fossil record
According to the fossil record, the divergence of coelacanths, lungfish, and tetrapods is thought to have occurred during the Silurian. Over 100 fossil species of coelacanth have been described. The oldest identified coelacanth fossils are around 420–410 million years old, dating to the early Devonian. Coelacanths were never a diverse group in comparison to other groups of fish, and reached a peak diversity during the Early Triassic (252–247 million years ago), coinciding with a burst of diversification between the Late Permian and Middle Triassic. Most Mesozoic coelacanths belong to the order Latimerioidei, which contains two major subdivisions, the marine Latimeriidae, which contains modern coelacanths, as well as the extinct Mawsoniidae, which were native to brackish, freshwater as well as marine environments. | Coelacanth | Wikipedia | 481 | 45503 | https://en.wikipedia.org/wiki/Coelacanth | Biology and health sciences | Fishes | null |
Paleozoic coelacanths are generally small (~ in length), while Mesozoic forms were larger. Several specimens belonging to the Jurassic and Cretaceous mawsoniid coelacanth genera Trachymetopon and Mawsonia likely reached or exceeded in length, making them amongst the largest known fishes of the Mesozoic, and amongst the largest bony fishes of all time.
The most recent fossil latimeriid is Megalocoelacanthus dobiei, whose disarticulated remains are found in late Santonian to middle Campanian, and possibly earliest Maastrichtian-aged marine strata of the Eastern and Central United States, the most recent mawsoniids are Axelrodichthys megadromos from early Campanian to early Maastrichtian freshwater continental deposits of France, as well as an indeterminate marine mawsoniid from Morocco, dating to the late Maastrichtian A small bone fragment from the European Paleocene has been considered the only plausible post-Cretaceous record, but this identification is based on comparative bone histology methods of doubtful reliability.
Living coelacanths have been considered "living fossils" based on their supposedly conservative morphology relative to fossil species; however, recent studies have expressed the view that coelacanth morphologic conservatism is a belief not based on data. Fossils suggest that coelacanths were most morphologically diverse during the Devonian and Carboniferous, while Mesozoic species are generally morphologically similar to each other.
Timeline of genera
Distribution and habitat | Coelacanth | Wikipedia | 320 | 45503 | https://en.wikipedia.org/wiki/Coelacanth | Biology and health sciences | Fishes | null |
The current coelacanth range is primarily along the eastern African coast, although Latimeria menadoensis was discovered off Indonesia. Coelacanths have been found in the waters of Kenya, Tanzania, Mozambique, South Africa, Madagascar, Comoros and Indonesia. Most Latimeria chalumnae specimens that have been caught have been captured around the islands of Grande Comore and Anjouan in the Comoros Archipelago (Indian Ocean). Though there are cases of L. chalumnae caught elsewhere, amino acid sequencing has shown no big difference between these exceptions and those found around Comore and Anjouan. Even though these few may be considered strays, there are several reports of coelacanths being caught off the coast of Madagascar. This leads scientists to believe that the endemic range of Latimeria chalumnae coelacanths stretches along the eastern coast of Africa from the Comoros Islands, past the western coast of Madagascar to the South African coastline. Mitochondrial DNA sequencing of coelacanths caught off the coast of southern Tanzania suggests a divergence of the two populations some 200,000 years ago. This could refute the theory that the Comoros population is the main population while others represent recent offshoots. A live specimen was seen and recorded on video in November 2019 at off the village of Umzumbe on the South Coast of KwaZulu-Natal, south of the iSimangaliso Wetland Park. This is the farthest south since the original discovery, and the second shallowest record after in the Diepgat Canyon. These sightings suggest that they may live shallower than previously thought, at least at the southern end of their range, where colder, better-oxygenated water is available at shallower depths.
The geographical range of the Indonesia coelacanth, Latimeria menadoensis, is believed to be off the coast of Manado Tua Island, Sulawesi, Indonesia, in the Celebes Sea. Key components confining coelacanths to these areas are food and temperature restrictions, as well as ecological requirements such as caves and crevices that are well-suited for drift feeding. Teams of researchers using submersibles have recorded live sightings of the fish in the Sulawesi Sea as well as in the waters of Biak in Papua. | Coelacanth | Wikipedia | 469 | 45503 | https://en.wikipedia.org/wiki/Coelacanth | Biology and health sciences | Fishes | null |
Anjouan Island and the Grande Comore provide ideal underwater cave habitats for coelacanths. The islands' underwater volcanic slopes, steeply eroded and covered in sand, house a system of caves and crevices which allow coelacanths resting places during the daylight hours. These islands support a large benthic fish population that helps to sustain coelacanth populations.
During the daytime, coelacanths rest in caves anywhere from deep. Others migrate to deeper waters. The cooler waters (below ) reduce the coelacanths' metabolic costs. Drifting toward reefs and night feeding saves vital energy. Resting in caves during the day also saves energy that otherwise would be expended to fight currents.
Behavior
Coelacanth locomotion is unique. To move around they most commonly take advantage of up- or down-wellings of current and drift. Their paired fins stabilize movement through the water. While on the ocean floor, they do not use the paired fins for any kind of movement. Coelacanths generate thrust with their caudal fins for quick starts. Due to the abundance of its fins, the coelacanth has high maneuverability and can orient its body in almost any direction in the water. They have been seen doing headstands as well as swimming belly up. It is thought that the rostral organ helps give the coelacanth electroreception, which aids in movement around obstacles.
Coelacanths are fairly peaceful when encountering others of their kind. They do avoid body contact, however, withdrawing immediately if contact occurs. When approached by foreign potential predators (e.g. a submersible), they show panic flight reactions, suggesting that coelacanths are most likely prey to large deepwater predators. Shark bite marks have been seen on coelacanths; sharks are common in areas inhabited by coelacanths. Electrophoresis testing of 14 coelacanth enzymes shows little genetic diversity between coelacanth populations. Among the fish that have been caught were about equal numbers of males and females. Population estimates range from 210 individuals per population to 500 per population. Because coelacanths have individual color markings, scientists think that they recognize other coelacanths via electric communication. | Coelacanth | Wikipedia | 459 | 45503 | https://en.wikipedia.org/wiki/Coelacanth | Biology and health sciences | Fishes | null |
Feeding
Coelacanths are nocturnal piscivores that feed mainly on benthic smaller fish and various cephalopods. They are "passive drift feeders", slowly drifting along currents with only minimal self-propulsion, eating whatever prey they encounter. Coelacanths also use their rostral organ for its electroreception to be able to detect nearby prey in low light settings.
Life history
Coelacanths are ovoviviparous, meaning that the female retains the fertilized eggs within her body while the embryos develop during a gestation period of five years. Typically, females are larger than the males; their scales and the skin folds around the cloaca differ. The male coelacanth has no distinct copulatory organs, just a cloaca, which has a urogenital papilla surrounded by erectile caruncles. It is hypothesized that the cloaca everts to serve as a copulatory organ.
Coelacanth eggs are large, with only a thin layer of membrane to protect them. Embryos hatch within the female and eventually are born alive, which is a rarity in fish. This was only discovered when the American Museum of Natural History dissected its first coelacanth specimen in 1975 and found it pregnant with five embryos. Young coelacanths resemble the adult, the main differences being an external yolk sac, larger eyes relative to body size and a more pronounced downward slope of the body. The juvenile coelacanth's broad yolk sac hangs below the pelvic fins. The scales and fins of the juvenile are completely matured; however, it does lack odontodes, which it gains during maturation.
A study that assessed the paternity of the embryos inside two coelacanth females indicated that each clutch was sired by a single male. This could mean that females mate monandrously, i.e. with one male only. Polyandry, female mating with multiple males, is common in both plants and animals and can be advantageous (e.g. insurance against mating with an infertile or incompatible mate), but also confers costs (increased risk of infection, danger of falling prey to predators, increased energy input when searching for new males). | Coelacanth | Wikipedia | 476 | 45503 | https://en.wikipedia.org/wiki/Coelacanth | Biology and health sciences | Fishes | null |
Conservation
Because little is known about the coelacanth, the conservation status is difficult to characterize. According to Fricke et al. (1995), it is important to conserve the species. From 1988 to 1994, Fricke counted some 60 individuals of L. chalumnae on each dive. In 1995 that number dropped to 40. Even though this could be a result of natural population fluctuation, it also could be a result of overfishing. The IUCN currently classifies L. chalumnae as "critically endangered", with a total population size of 500 or fewer individuals. L. menadoensis is considered Vulnerable, with a significantly larger population size (fewer than 10,000 individuals).
The major threat towards the coelacanth is the accidental capture by fishing operations, especially commercial deep-sea trawling. Coelacanths usually are caught when local fishermen are fishing for oilfish. Fishermen sometimes snag a coelacanth instead of an oilfish because they traditionally fish at night, when oilfish (and coelacanths) feed.
Before scientists became interested in coelacanths, they were thrown back into the water if caught. Now that they are recognized as important, fishermen trade them to scientists or other officials. Before the 1980s, this was a problem for coelacanth populations. In the 1980s, international aid gave fiberglass boats to the local fishermen, which moved fishing beyond the coelacanth territories into more productive waters. Since then, most of the motors on the boats failed, forcing the fishermen back into coelacanth territory and putting the species at risk again.
Methods to minimize the number of coelacanths caught include moving fishers away from the shore, using different laxatives and malarial salves to reduce the demand for oilfish, using coelacanth models to simulate live specimens, and increasing awareness of the need for conservation. In 1987 the Coelacanth Conservation Council advocated the conservation of coelacanths. The CCC has branches located in Comoros, South Africa, Canada, the United Kingdom, the U.S., Japan, and Germany. The agencies were established to help protect and encourage population growth of coelacanths. | Coelacanth | Wikipedia | 458 | 45503 | https://en.wikipedia.org/wiki/Coelacanth | Biology and health sciences | Fishes | null |
A "deep release kit" was developed in 2014 and distributed by private initiative, consisting of a weighted hook assembly that allows a fisherman to return an accidentally caught coelacanth to deep waters where the hook can be detached once it hits the seafloor. Conclusive reports about the effectiveness of this method are still pending.
In 2002, the South African Coelacanth Conservation and Genome Resource Programme was launched to help further the studies and conservation of the coelacanth. This program focuses on biodiversity conservation, evolutionary biology, capacity building, and public understanding. The South African government committed to spending R10 million on the program. In 2011, a plan was made for a Tanga Coelacanth Marine Park to conserve biodiversity for marine animals including the coelacanth. The park was designed to reduce habitat destruction and improve prey availability for endangered species.
Human consumption
Coelacanths are considered a poor source of food for humans and likely most other fish-eating animals. Coelacanth flesh has large amounts of oil, urea, wax esters, and other compounds that give the flesh a distinctly unpleasant flavor, make it difficult to digest, and can cause diarrhea. Their scales themselves secrete mucus, which combined with the excessive oil their bodies produce, make coelacanths a slimy food. Where the coelacanth is more common, local fishermen avoid it because of its potential to sicken consumers. As a result, the coelacanth has no real commercial value apart from being coveted by museums and private collectors.
Cultural significance
Because of the surprising nature of the coelacanth's discovery, they have been a frequent source of inspiration in modern artwork, craftsmanship, and literature. At least 22 countries have depicted them on their postage stamps, particularly the Comoros, which has issued 12 different sets of coelacanth stamps. The coelacanth is also depicted on the 1000 Comorian franc banknote, as well as the 5 CF coin.
In the Pokémon media franchise, the Pokémon known as Relicanth is based on the coelacanth.
In the video game series Animal Crossing, the coelacanth is a rare fish that can be caught by the player by fishing in the ocean. | Coelacanth | Wikipedia | 458 | 45503 | https://en.wikipedia.org/wiki/Coelacanth | Biology and health sciences | Fishes | null |
The treeshrews (also called tree shrews or banxrings) are small mammals native to the tropical forests of South and Southeast Asia. They make up the entire order Scandentia (from Latin scandere, "to climb"), which split into two families: the Tupaiidae (19 species, "ordinary" treeshrews), and the Ptilocercidae (one species, the pen-tailed treeshrew).
Though called 'treeshrews', and despite having previously been classified in Insectivora, they are not true shrews, and not all species live in trees. They are omnivores; among other things, treeshrews eat fruit. As fellow members of Euarchonta, treeshrews are closely related to primates, and have been used as an alternative to primates in experimental studies of myopia, psychosocial stress, and hepatitis.
Description
Treeshrews are slender animals with long tails and soft, greyish to reddish-brown fur. The terrestrial species tend to be larger than the arboreal forms, and to have larger claws, which they use for digging up insect prey. They have poorly developed canine teeth and unspecialised molars, with an overall dental formula of They have a higher brain to body mass ratio than any other mammal, including humans, but high ratios are not uncommon for animals weighing less than .
Treeshrews have good vision, which is binocular in the case of the more arboreal species.
Reproduction
Female treeshrews have a gestation period of 45–50 days and give birth to up to three young in nests lined with dry leaves inside tree hollows. The young are born blind and hairless, but are able to leave the nest after about a month. During this period, the mother provides relatively little maternal care, visiting her young only for a few minutes every other day to suckle them.
Treeshrews reach sexual maturity after around four months, and breed for much of the year, with no clear breeding season in most species.
Behavior
Treeshrews live in small family groups, which defend their territory from intruders. Most are diurnal, although the pen-tailed treeshrew is nocturnal.
They mark their territories using various scent glands or urine, depending on the particular species.
Diet
Treeshrews are omnivorous, feeding on insects, small vertebrates, fruit, and seeds. Among other things, treeshrews eat Rafflesia fruit. | Treeshrew | Wikipedia | 510 | 45511 | https://en.wikipedia.org/wiki/Treeshrew | Biology and health sciences | Mammals: General | Animals |
The pen-tailed treeshrew in Malaysia is able to consume large amounts of naturally fermented nectar from flower buds of the bertam palm Eugeissona tristis (with up to 3.8% alcohol content) the entire year without it having any effects on behaviour.
Treeshrews have also been observed intentionally eating foods high in capsaicin, a behavior unique among mammals other than humans. A single TRPV1 mutation reduces their pain response to capsaicinoids, which scientists believe is an evolutionary adaptation to be able to consume spicy foods in their natural habitats.
Pitcher plants like the Nepenthes lowii, supplements its carnivorous diet with tree shrew droppings.
Taxonomy
Treeshrews were moved from the order Insectivora into the order Primates because of certain internal similarities to primates (for example, similarities in the brain anatomy, highlighted by Sir Wilfrid Le Gros Clark), and classified as a "primitive prosimian", however they were soon split from the primates and moved into their own clade. Taxonomists continue to refine the treeshrews' relations to primates and to other closely related clades.
Molecular phylogenetic studies have suggested that the treeshrews should be given the same rank (order) as the primates and, with the primates and the flying lemurs (colugos), belong to the grandorder Euarchonta. According to this classification, the Euarchonta are sister to the Glires (lagomorphs and rodents), and the two groups are combined into the superorder Euarchontoglires. However, the alternative placement of treeshrews as sister to both Glires and Primatomorpha cannot be ruled out. Some studies place Scandentia as sister of the Glires, which would invalidate Euarchonta: It is this organization that is shown in the tree diagram below. | Treeshrew | Wikipedia | 396 | 45511 | https://en.wikipedia.org/wiki/Treeshrew | Biology and health sciences | Mammals: General | Animals |
Several other arrangements of these orders have been proposed in the past, and the above tree is only a well-favored proposal. Although it is known that Scandentia is one of the most basal euarchontoglire clades, the exact phylogenetic position is not yet considered resolved: It may be a sister of Glires, Primatomorpha, or Dermoptera, or separate from and sister to all other Euarchontoglires. Shared short interspersed nuclear elements (SINEs) offer strong evidence for Scandentia belonging to the Euarchonta group:
Order Scandentia
The 23 species are placed in four genera, which are divided into two families. The majority are in the "ordinary" treeshrew family, Tupaiidae, but one species, the pen-tailed treeshrew, is different enough to warrant placement in its own family, Ptilocercidae; the two families are thought to have separated 60 million years ago. The former Tupaiidae genus Urogale was disbanded in 2011 when the Mindanao treeshrew was moved to Tupaia based on a molecular phylogeny.
Family Tupaiidae
Genus Anathana
Madras treeshrew, A. ellioti
Genus Dendrogale
Bornean smooth-tailed treeshrew, D. melanura
Northern smooth-tailed treeshrew, D. murina
Genus Tupaia
Northern treeshrew, T. belangeri
Golden-bellied treeshrew, T. chrysogaster
Bangka Island treeshrew, T. discolor
Striped treeshrew, T. dorsalis
Mindanao treeshrew, T. everetti
Sumatran treeshrew, T. ferruginea
Common treeshrew, T. glis
Slender treeshrew, T. gracilis
Javan treeshrew, T. hypochrysa
Horsfield's treeshrew, T. javanica
Long-footed treeshrew, T. longipes
Pygmy treeshrew, T. minor
Mountain treeshrew, T. montana
Nicobar treeshrew, T. nicobarica
Palawan treeshrew, T. palawanensis
Painted treeshrew, T. picta
Kalimantan treeshrew, T. salatana
Ruddy treeshrew, T. splendidula
Large treeshrew, T. tana
Family Ptilocercidae
Genus Ptilocercus
Pen-tailed treeshrew, P. lowii | Treeshrew | Wikipedia | 509 | 45511 | https://en.wikipedia.org/wiki/Treeshrew | Biology and health sciences | Mammals: General | Animals |
Fossil record
The fossil record of treeshrews is poor. The oldest putative treeshrew, Eodendrogale parva, is from the Middle Eocene of Henan, China, but the identity of this animal is uncertain. Other fossils have come from the Miocene of Thailand, Pakistan, India, and Yunnan, China, as well as the Pliocene of India. Most belong to the family Tupaiidae; one fossil species described from the Oligocene of Yunnan is thought to be closer to the pen-tailed treeshrew.
Named fossil species include Prodendrogale yunnanica, Prodendrogale engesseri, and Tupaia storchi from Yunnan, Tupaia miocenica from Thailand, Palaeotupaia sivalicus from India and Ptilocercus kylin from Yunnan. | Treeshrew | Wikipedia | 173 | 45511 | https://en.wikipedia.org/wiki/Treeshrew | Biology and health sciences | Mammals: General | Animals |
The Strepsiptera () are an order of insects with eleven extant families that include about 600 described species. They are endoparasites of other insects, such as bees, wasps, leafhoppers, silverfish, and cockroaches. Females of most species never emerge from the host after entering its body, finally dying inside it. The early-stage larvae do emerge because they must find an unoccupied living host, and the short-lived males must emerge to seek a receptive female in her host. They are believed to be most closely related to beetles, from which they diverged 300–350 million years ago, but do not appear in the fossil record until the mid-Cretaceous around 100 million years ago.
The order is not well known to non-specialists, and the nearest they have to a common name is stylops, in reference to the genus Stylops. The name of the order translates to "twisted wing", giving rise to other common names used for the order, twisted-wing insects and twisted-winged parasites.
Adult males are rarely observed, although specimens may be lured using cages containing virgin females. Nocturnal specimens can also be collected at light traps.
Biology
Appearance and structure
Males
Males of the Strepsiptera have wings, legs, eyes, and antennae, though their mouthparts cannot be used for feeding. Many have mouthparts modified into sensory structures. The males bear a superficial resemblance to flies. The forewings are modified into small club-shaped structures called halteres, which sense gyroscopic information. A similar organ exists in flies, though in that group the hindwings are modified instead, and the two groups are thought to have independently evolved the structures. The hindwings are generally fan-shaped, and have strongly reduced venation. The antennae are flabellate, and are covered in specialised chemoreceptors, likely to detect females over long distances.
Adult male Strepsiptera have eyes unlike those of any other insect, resembling the eyes found in the trilobite group Phacopina. Instead of a compound eye consisting of hundreds to thousands of ommatidia, that each produce a pixel of the entire image, the strepsipteran eyes consist of only a few dozen "eyelets" that each produce a complete image. These eyelets are separated by cuticle and/or setae, giving the cluster eye as a whole a blackberry-like appearance. | Strepsiptera | Wikipedia | 498 | 45598 | https://en.wikipedia.org/wiki/Strepsiptera | Biology and health sciences | Insects: General | Animals |
Females
The females of Stylopidia, which includes 97% of all described strepsipteran species and all modern strepsipteran families except Mengenillidae and Bahiaxenidae, are not known to leave their hosts and are neotenic in form, lacking wings, legs, and eyes, but have a well sclerotised cephalothorax (fused head and thorax). Adult female mengenillids are wingless but are free living and somewhat mobile with legs and small eyes. This is probably also true for the bahiaxenids, though this has not been observed.
Larvae
Newly hatched primary (first instar) larvae are on average in length, smaller than many single-celled organisms. They are highly mobile with well developed stemmata, which are able to distinguish color. The underside of the body is covered in minute hair-like structures (microtrichia), which allow the larvae to stick to wet surfaces via capillary action. At the back of the body are well developed large bristle-like cerci, which are attached to muscles, which allow the larvae to jump. The tarsal segment of their legs have structures which allow them to cling to their hosts. Later larval instars which develop inside the host are completely immobile.
Life cycle
Virgin females release a pheromone which the males use to locate them. Mating in at least some species is polyandrous, where the female mates with more than one male.
In the Stylopidia, the female's anterior region protrudes out between the segments of the host's abdomen. In all strepsipterans the male mates by rupturing the female's cuticle (in the case of Stylopidia, this is in a deep narrow fissure of the cephalothorax near the birth canal). Sperm passes through the opening directly into the body in a process called traumatic insemination, which has independently evolved in some other insects like bed bugs. | Strepsiptera | Wikipedia | 420 | 45598 | https://en.wikipedia.org/wiki/Strepsiptera | Biology and health sciences | Insects: General | Animals |
Strepsiptera eggs hatch inside the female, and the planidium larvae can move around freely within the female's haemocoel; this behavior is unique to these insects. The offspring consume their mother from the inside in a process known as haemocoelous viviparity. Each female produces many thousands of planidium larvae. The larvae emerge from the brood opening/canal on the female's head, which protrudes outside the host body.
Larvae have legs and actively seek out new hosts. Their legs are partly vestigial in that they lack a trochanter, the leg segment that forms the articulation between the basal coxa and the femur. The larvae are very active as they only have a limited amount of time to find a host before they exhaust their energy reserves. These first-instar larvae have stemmata (simple, single-lens eyes). When the larvae latch onto a host, they enter it by secreting enzymes that soften the cuticle, usually in the abdominal region of the host. Some species have been reported to enter the eggs of hosts. Larvae of Stichotrema dallatorreanum Hofeneder from Papua New Guinea were found to enter their orthopteran host's tarsus (foot).
Once inside the host, they undergo hypermetamorphosis and transform into a less-mobile, legless larval form. They induce the host to produce a bag-like structure inside which they feed and grow. This structure, made from host tissue, protects them from the immune defences of the host. Larvae go through four more instars, and in each moult the older cuticle separates but is not discarded ("apolysis without ecdysis"), so multiple layers form around the larvae. Male larvae pupate after the last moult, but females directly become neotenous adults. The colour and shape of the host's abdomen may be changed and the host usually becomes sterile. The parasites then undergo pupation to become adults. Adult males emerge from the host bodies, while females stay inside. Females may occupy up to 90% of the abdominal volume of their hosts. Adult males are very short-lived, usually surviving less than five hours, and do not feed. | Strepsiptera | Wikipedia | 468 | 45598 | https://en.wikipedia.org/wiki/Strepsiptera | Biology and health sciences | Insects: General | Animals |
Parasitism
Strepsiptera of various species have been documented to attack hosts in many orders, including members of the orders Zygentoma (silverfish and allies), Orthoptera (grasshoppers, crickets), Blattodea (cockroaches), Mantodea (praying mantis), Heteroptera (bugs), Hymenoptera (wasps, ants and bees), and Diptera (flies). In the strepsipteran family Myrmecolacidae, the males parasitize ants, while the females parasitize Orthoptera. Members of Mengenillidae target Zygentoma exclusively, while Stylopidia targets only winged insects, with a large number of stylopidians targeting wasps and bees, while the largest family of strepsipterans, the Stylopidae, with over 27% of all described strepsipterans, targets bees exclusively.
Very rarely, multiple females may live within a single stylopized host; multiple males within a single host are somewhat more common.
Strepsiptera of the family Myrmecolacidae can influence their host's behaviour, causing their ant hosts to linger on the tips of grass leaves, increasing the chance of being found by strepsipteran males (in the case of females) and putting them in a good position for male emergence (in the case of males).
Taxonomy
The order, named by William Kirby in 1813, is named for the hindwings, which are held at a twisted angle when at rest (from Greek (), to twist; and (), wing). The forewings are reduced to halteres. | Strepsiptera | Wikipedia | 358 | 45598 | https://en.wikipedia.org/wiki/Strepsiptera | Biology and health sciences | Insects: General | Animals |
Strepsiptera were once believed to be the sister group to the beetle families Meloidae and Ripiphoridae, which have similar parasitic development and forewing reduction. Early molecular research suggested their inclusion as a sister group to the flies, in a clade called Halteria, which have one pair of the wings modified into halteres, and failed to support their relationship to the beetles. Further molecular studies, however, suggested they are outside the clade Mecopterida (containing the Diptera and Lepidoptera), but found no strong evidence for affinity with any other extant group. Study of their evolutionary position has been problematic due to difficulties in phylogenetic analysis arising from long branch attraction. Most modern molecular studies find strepsipterans as the sister group of beetles (Coleoptera), with both groups together forming the clade Coleopterida. The most basal strepsipteran is the fossil Protoxenos janzeni discovered in Eocene aged Baltic amber, while the most basal living strepsipteran is Bahiaxenos relictus, the sole member of the family Bahiaxenidae. The earliest known strepsipteran fossils are those of Cretostylops engeli (Cretostylopdiae) and Kinzelbachilla ellenbergeri, Phthanoxenos nervosus and Heterobathmilla kakopoios (Phthanoxenidae), discovered in middle Cretaceous Burmese amber from Myanmar, around 99 million years old, which all lie outside the crown group, but are all more closely related to modern strepsiperans than Protoxenos is. The finding of a parasitic first instar in the same deposit indicates that the parasitic lifestyle of the group has likely existed nearly unchanged for 100 million years, though their evolutionary history prior to this remains a mystery. The idea that mengellinids' targeting of zygentomans represents the ancestral ecology of the group as a whole has been considered questionable.
Families | Strepsiptera | Wikipedia | 411 | 45598 | https://en.wikipedia.org/wiki/Strepsiptera | Biology and health sciences | Insects: General | Animals |
The vast majority of living strepispterans are placed within the grouping Stylopidia, which includes the families Corioxenidae, Halictophagidae, Callipharixenidae, Bohartillidae, Elenchidae, Myrmecolacidae, Stylopidae, Protelencholacidae (extinct) and Xenidae. All Stylopidia have endoparasitic females having multiple genital openings. Two living families, Mengenillidae and Bahiaxenidae, are placed outside of this group, along with several extinct families.
The Stylopidae have four-segmented tarsi and four- to six-segmented antennae, with the third segment having a lateral process. The family Stylopidae may be paraphyletic. The Elenchidae have two-segmented tarsi and four-segmented antennae, with the third segment having a lateral process. The Halictophagidae have three-segmented tarsi and seven-segmented antennae, with lateral processes from the third and fourth segments.
The Stylopidae mostly parasitize wasps and bees, the Elenchidae are known to parasitize Fulgoroidea, while the Halictophagidae are found on leafhoppers, treehoppers, and mole cricket hosts.
Strepsipteran insects in the genus Xenos parasitize Polistes carnifex, a species of social wasps. These obligate parasites infect the developing wasp larvae in the nest and are present within the abdomens of female wasps when they hatch out. Here they remain until they thrust through the cuticle and pupate (males) or release infective first-instar larvae onto flowers (females). These larvae are transported back to their nests by foraging wasps.
Cladogram
After:
Relationship with humans
Some insects which have been considered pests may have strepsipteran endoparasites. Inoculation of a pest population with the corresponding parasitoid may sometimes aid in reducing the impact of such pests, although no strepsipterans have ever been tested for use in this capacity, let alone being available for such purposes, either commercially or experimentally. | Strepsiptera | Wikipedia | 472 | 45598 | https://en.wikipedia.org/wiki/Strepsiptera | Biology and health sciences | Insects: General | Animals |
Surgery is a medical specialty that uses manual and instrumental techniques to diagnose or treat pathological conditions (e.g., trauma, disease, injury, malignancy), to alter bodily functions (e.g., malabsorption created by bariatric surgery such as gastric bypass), to reconstruct or alter aesthetics and appearance (cosmetic surgery), or to remove unwanted tissues (body fat, glands, scars or skin tags) or foreign bodies.
The act of performing surgery may be called a surgical procedure or surgical operation, or simply "surgery" or "operation". In this context, the verb "operate" means to perform surgery. The adjective surgical means pertaining to surgery; e.g. surgical instruments, surgical facility or surgical nurse. Most surgical procedures are performed by a pair of operators: a surgeon who is the main operator performing the surgery, and a surgical assistant who provides in-procedure manual assistance during surgery. Modern surgical operations typically require a surgical team that typically consists of the surgeon, the surgical assistant, an anaesthetist (often also complemented by an anaesthetic nurse), a scrub nurse (who handles sterile equipment), a circulating nurse and a surgical technologist, while procedures that mandate cardiopulmonary bypass will also have a perfusionist. All surgical procedures are considered invasive and often require a period of postoperative care (sometimes intensive care) for the patient to recover from the iatrogenic trauma inflicted by the procedure. The duration of surgery can span from several minutes to tens of hours depending on the specialty, the nature of the condition, the target body parts involved and the circumstance of each procedure, but most surgeries are designed to be one-off interventions that are typically not intended as an ongoing or repeated type of treatment.
In British colloquialism, the term "surgery" can also refer to the facility where surgery is performed, or simply the office/clinic of a physician, dentist or veterinarian.
Definitions | Surgery | Wikipedia | 409 | 45599 | https://en.wikipedia.org/wiki/Surgery | Biology and health sciences | Health, fitness, and medicine | null |
As a general rule, a procedure is considered surgical when it involves cutting of a person's tissues or closure of a previously sustained wound. Other procedures that do not necessarily fall under this rubric, such as angioplasty or endoscopy, may be considered surgery if they involve "common" surgical procedure or settings, such as use of antiseptic measures and sterile fields, sedation/anesthesia, proactive hemostasis, typical surgical instruments, suturing or stapling. All forms of surgery are considered invasive procedures; the so-called "noninvasive surgery" ought to be more appropriately called minimally invasive procedures, which usually refers to a procedure that utilizes natural orifices (e.g. most urological procedures) or does not penetrate the structure being excised (e.g. endoscopic polyp excision, rubber band ligation, laser eye surgery), are percutaneous (e.g. arthroscopy, catheter ablation, angioplasty and valvuloplasty), or to a radiosurgical procedure (e.g. irradiation of a tumor). | Surgery | Wikipedia | 244 | 45599 | https://en.wikipedia.org/wiki/Surgery | Biology and health sciences | Health, fitness, and medicine | null |
Types of surgery
Surgical procedures are commonly categorized by urgency, type of procedure, body system involved, the degree of invasiveness, and special instrumentation.
Based on timing:
Elective surgery is done to correct a non-life-threatening condition, and is carried out at the person's convenience, or to the surgeon's and the surgical facility's availability.
Semi-elective surgery is one that is better done early to avoid complications or potential deterioration of the patient's condition, but such risk are sufficiently low that the procedure can be postponed for a short period time.
Emergency surgery is surgery which must be done without any delay to prevent death or serious disabilities or loss of limbs and functions.
Based on purpose:
Exploratory surgery is performed to establish or aid a diagnosis.
Therapeutic surgery is performed to treat a previously diagnosed condition.
Curative surgery is a therapeutic procedure done to permanently remove a pathology.
Plastic surgery is done to improve a body part's function or appearance.
Reconstructive plastic surgery is done to improve the function or subjective appearance of a damaged or malformed body part.
Cosmetic surgery is done to subjectively improve the appearance of an otherwise normal body part.
Bariatric surgery is done to assist weight loss when dietary and pharmaceutical methods alone have failed.
Non-survival surgery, or terminal surgery, is where Euthanasia is performed while the subject is under Anesthesia so that the subject will not regain conscious pain perception. This type of surgery is usually done in Animal testing experiments. | Surgery | Wikipedia | 304 | 45599 | https://en.wikipedia.org/wiki/Surgery | Biology and health sciences | Health, fitness, and medicine | null |
By type of procedure:
Amputation involves removing an entire body part, usually a limb or digit; castration is the amputation of testes; circumcision is the removal of prepuce from the penis or clitoral hood from the clitoris (see female circumcision). Replantation involves reattaching a severed body part.
Resection is the removal of all or part of an internal organ and/or connective tissue. A segmental resection specifically removes an independent vascular region of an organ such as a hepatic segment, a bronchopulmonary segment or a renal lobe. Excision is the resection of only part of an organ, tissue or other body part (e.g. skin) without discriminating specific vascular territories. Exenteration is the complete removal of all organs and soft tissue content (especially lymphoid tissues) within a body cavity.
Extirpation is the complete excision or surgical destruction of a body part.
Ablation is destruction of tissue through the use of energy-transmitting devices such as electrocautery/fulguration, laser, focused ultrasound or freezing.
Repair involves the direct closure or restoration of an injured, mutilated or deformed organ or body part, usually by suturing or internal fixation. Reconstruction is an extensive repair of a complex body part (such as joints), often with some degrees of structural/functional replacement and commonly involves grafting and/or use of implants.
Grafting is the relocation and establishment of a tissue from one part of the body to another. A flap is the relocation of a tissue without complete separation of its original attachment, and a free flap is a completely detached flap that carries an intact neurovascular structure ready for grafting onto a new location.
Bypass involves the relocation/grafting of a tubular structure onto another in order to reroute the content flow of that target structure from a specific segment directly to a more distal ("downstream") segment.
Implantation is insertion of artificial medical devices to replace or augment existing tissue.
Transplantation is the replacement of an organ or body part by insertion of another from a different human (or animal) into the person undergoing surgery. Harvesting is the resection of an organ or body part from a live human or animal (known as the donor) for transplantation into another patient (known as the recipient). | Surgery | Wikipedia | 494 | 45599 | https://en.wikipedia.org/wiki/Surgery | Biology and health sciences | Health, fitness, and medicine | null |
By organ system: Surgical specialties are traditionally and academically categorized by the organ, organ system or body region involved. Examples include:
Cardiac surgery — the heart and mediastinal great vessels;
Thoracic surgery — the thoracic cavity including the lungs;
Gastrointestinal surgery — the digestive tract and its accessory organs;
Vascular surgery — the extra-mediastinal great vessels and peripheral circulatory system;
Urological surgery — the genitourinary system;
ENT surgery — ear, nose and throat, also known as head and neck surgery when including the neck region;
Oral and maxillofacial surgery — the oral cavity, jaws, and face;
Neurosurgery — the central nervous system, and;
Orthopedic surgery — the musculoskeletal system.
By degree of invasiveness of surgical procedures:
Conventional open surgery (such as a laparotomy) requires a large incision to access the area of interest, and directly exposes the internal body cavity to the outside.
Minimally-invasive surgery involves much smaller surface incisions or even natural orifices (nostril, mouth, anus or urethra) to insert miniaturized instruments within a body cavity or structure, as in laparoscopic surgery or angioplasty.
Hybrid surgery uses a combination of open and minimally-invasive techniques, and may include hand ports or larger incisions to assist with performance of elements of the procedure.
By equipment used:
Laser surgery involves use of laser ablation to divide tissue instead of a scalpel, scissors or similar sharp-edged instruments.
Cryosurgery uses low-temperature cryoablation to freeze and destroy a target tissue.
Electrosurgery involves use of electrocautery to cut and coagulate tissue.
Microsurgery involves the use of an operating microscope for the surgeon to see and manipulate small structures.
Endoscopic surgery uses optical instruments to relay the image from inside an enclosed body cavity to the outside, and the surgeon performs the procedure using specialized handheld instruments inserted through trocars placed through the body wall. Most modern endoscopic procedures are video-assisted, meaning the images are viewed on a display screen rather than through the eyepiece on the endoscope.
Robotic surgery makes use of robotics such as the Da Vinci or the ZEUS robotic surgical systems, to remotely control endoscopic or minimally-invasive instruments. | Surgery | Wikipedia | 497 | 45599 | https://en.wikipedia.org/wiki/Surgery | Biology and health sciences | Health, fitness, and medicine | null |
Resection and excisional procedures start with a prefix for the target organ to be excised (cut out) and end in the suffix -ectomy. For example, removal of part of the stomach would be called a subtotal gastrectomy.
Procedures involving cutting into an organ or tissue end in -otomy. A surgical procedure cutting through the abdominal wall to gain access to the abdominal cavity is a laparotomy.
Minimally invasive procedures, involving small incisions through which an endoscope is inserted, end in -oscopy. For example, such surgery in the abdominal cavity is called laparoscopy.
Procedures for formation of a permanent or semi-permanent opening called a stoma in the body end in -ostomy, such as creation of a colostomy, a connection of colon and the abdominal wall. This prefix is also used for connection between two viscera, such as how an esophagojejunostomy refers to a connection created between the esophagus and the jejunum.
Plastic and reconstruction procedures start with the name for the body part to be reconstructed and end in -plasty. For example, rhino- is a prefix meaning "nose", therefore a rhinoplasty is a reconstructive or cosmetic surgery for the nose. A pyloroplasty refers to a type of reconstruction of the gastric pylorus.
Procedures that involve cutting the muscular layers of an organ end in -myotomy. A pyloromyotomy refers to cutting the muscular layers of the gastric pylorus.
Repair of a damaged or abnormal structure ends in -orraphy. This includes herniorrhaphy, another name for a hernia repair. | Surgery | Wikipedia | 361 | 45599 | https://en.wikipedia.org/wiki/Surgery | Biology and health sciences | Health, fitness, and medicine | null |
Reoperation, revision, or "redo" procedures refer to a planned or unplanned return to the operating theater after a surgery is performed to re-address an aspect of patient care. Unplanned reasons for reoperation include postoperative complications such as bleeding or hematoma formation, development of a seroma or abscess, anastomotic leak, tissue necrosis requiring debridement or excision, or in the case of malignancy, close or involved resection margins that may require re-excision to avoid local recurrence. Reoperation can be performed in the acute phase, or it can be also performed months to years later if the surgery failed to solve the indicated problem. Reoperation can also be planned as a staged operation where components of the procedure are performed or reversed under separate anesthesia. | Surgery | Wikipedia | 177 | 45599 | https://en.wikipedia.org/wiki/Surgery | Biology and health sciences | Health, fitness, and medicine | null |
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