text stringlengths 26 3.6k | page_title stringlengths 1 71 | source stringclasses 1
value | token_count int64 10 512 | id stringlengths 2 8 | url stringlengths 31 117 | topic stringclasses 4
values | section stringlengths 4 49 ⌀ | sublist stringclasses 9
values |
|---|---|---|---|---|---|---|---|---|
Robinson's estimation of P. robustus size was soon challenged in 1974 by American palaeontologist Stephen Jay Gould and English palaeoanthropologist David Pilbeam, who guessed from the available skeletal elements a weight of about . Similarly, in 1988, American anthropologist Henry McHenry reported much lighter weights as well as notable sexual dimorphism for Paranthropus. McHenry plotted body size vs. the cross sectional area of the femoral head for a sample of just humans and a sample with all great apes including humans, and calculated linear regressions for each one. Based on the average of these two regressions, he reported an average weight of for P. robustus using the specimens SK 82 and SK 97. In 1991, McHenry expanded his sample size, and also estimated the living size of Swartkrans specimens by scaling down the dimensions of an average modern human to meet a preserved leg or foot element (he considered the arm measurements too variable among hominins to give accurate estimates). At Members 1 and 2, about 35% of the P. robustus leg or foot specimens were the same size as those in a human, 22% in a human, and the remaining 43% bigger than the former but less than a human except for KNM‐ER 1464 (an ankle bone). At Member 3, all individuals were consistent with a human. Smaller adults thus seem to have been more common. McHenry also estimated the living height of three P. robustus specimens (male SK 82, male SK 97, and female or subadult SK 3155), by scaling down an average human to meet the estimated size of the preserved femur, as , , and , respectively. Based on just these three, he reported an average height of for P. robustus males and for females. | Paranthropus robustus | Wikipedia | 378 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
In 2001, palaeoanthropologist Randall L. Susman and colleagues, using two recently discovered proximal femoral fragments from Swartkrans, estimated an average of for males and for females. If these four proximal femur specimens—SK 82, SK 97, SKW 19, and SK 3121—are representative of the entire species, they said that this degree of sexual dimorphism is greater than what is exhibited in humans and chimpanzees, but less than orangutans and gorillas. Female P. robustus were about the same estimated weight as female H. ergaster/H. erectus in Swartkrans, but they estimated male H. ergaster/H. erectus as much bigger at . In 2012, American anthropologist Trenton Holliday, using the same equation as McHenry on three specimens, reported an average of with a range of . In 2015, biological anthropologist Mark Grabowski and colleagues, using nine specimens, estimated an average of for males and for females.
Palaeobiology
Diet | Paranthropus robustus | Wikipedia | 222 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
In 1954, Robinson suggested that the heavily built skull of P. robustus and resultantly exorbitant bite force was indicative of a specialist diet adapted for frequently cracking hard foods such as nuts. Because of this, the predominant model of Paranthropus extinction for the latter half of the 20th century was that they were unable to adapt to the volatile climate of the Pleistocene, unlike the much more adaptable Homo. Subsequent researchers reinforced this model studying the musculature of the face, dental wearing patterns, and primate ecology. In 1981, English anthropologist Alan Walker, while studying the P. boisei skulls KNM-ER 406 and 729, pointed out that bite force is a measure of not only the total pressure exerted but also the surface area of the tooth over which the pressure is being exerted, and Paranthropus teeth are 4–5 times the size of modern human teeth. Because the chewing muscles are arranged the same way, Walker postulated that the heavy build was instead an adaptation to chew a large quantity of food at the same time. He also found that microwearing on 20 P. boisei molar specimens were indistinguishable from patterning recorded in mandrills, chimps, and orangutans. Despite subsequent arguments that Paranthropus were not specialist feeders, the predominant consensus in favour of Robinson's initial model did not change for the remainder of the 20th century. | Paranthropus robustus | Wikipedia | 294 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
In 2004, in their review of Paranthropus dietary literature, anthropologists Bernard Wood and David Strait concluded that Paranthropus were most definitely generalist feeders, and that P. robustus was an omnivore. They found that the microwear patterns in P. robustus suggest hard food was infrequently consumed, and therefore the heavy build of the skull was only relevant when eating less desirable fallback foods. Such a strategy is similar to that used by modern gorillas, which can sustain themselves entirely on lower quality fallback foods year-round, as opposed to lighter built chimpanzees (and presumably gracile australopithecines) which require steady access to high quality foods. In 1980, anthropologists Tom Hatley and John Kappelman suggested that early hominins (convergently with bears and pigs) adapted to eating abrasive and calorie-rich underground storage organs (USOs), such as roots and tubers. Since then, hominin exploitation of USOs has gained more support. In 2005, biological anthropologists Greg Laden and Richard Wrangham proposed that Paranthropus relied on USOs as a fallback or possibly primary food source, and noted that there may be a correlation between high USO abundance and hominin occupation. | Paranthropus robustus | Wikipedia | 271 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
A 2006 carbon isotope analysis suggested that P. robustus subsisted on mainly C4 savanna plants or C3 forest plants depending on the season, which could indicate either seasonal shifts in diet or seasonal migration from forest to savanna. H. ergaster/H. erectus appears to have consumed about the same proportion of C3 to C4 based foods as P. robustus. P. robustus likely also commonly cracked hard foods such as seeds or nuts, as it had a moderate tooth-chipping rate (about 12% in a sample of 239 individuals, as opposed to little to none for P. boisei). A high cavity rate could indicate honey consumption. Juvenile P. robustus may have relied more on tubers than adults, given the elevated levels of strontium compared to adults in teeth from Swartkrans Cave, which, in the area, was most likely sourced from tubers. Dentin exposure on juvenile teeth could indicate early weaning, or a more abrasive diet than adults which wore away the cementum and enamel coatings, or both. It is also possible juveniles were instead less capable of removing grit from dug-up food rather than purposefully seeking out more abrasive foods.
Social structure
Given the marked anatomical and physical differences with modern great apes, there may be no modern analogue for australopithecine societies, so comparisons drawn with modern primates are highly speculative.
In 2007, anthropologist Charles Lockwood and colleagues pointed out that P. robustus appears to have had pronounced sexual dimorphism, with males notably larger than females. This is commonly correlated with a male-dominated polygamous society, such as the harem society of modern forest-dwelling silverback gorillas where one male has exclusive breeding rights to a group of females. Estimated male-female size disparity in P. robustus is comparable to gorillas (based on facial dimensions), and younger males were less robust than older males (delayed maturity is also exhibited in gorillas). Because the majority of sexed P. robustus specimens are male (or at least presumed male), males seem to have had a higher mortality rate than females. In a harem society, males are more likely to be evicted from the group given higher male–male competition over females, and lone males may have been put at a higher risk of predation. By this hypothesis, a female moving out of her birth group may have spent little time alone and transferred immediately to another established group. | Paranthropus robustus | Wikipedia | 511 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
However, in 2011, palaeoanthropologist Sandi Copeland and colleagues studied the strontium isotope ratio of P. robustus teeth from the dolomite Sterkfontein Valley, and found that like other hominins, but unlike other great apes, P. robustus females were more likely to leave their place of birth (patrilocal). This discounts the plausibility of a harem society, which would have resulted in a matrilocal society due to heightened male–male competition. Males did not seem to have ventured very far from the valley, which could either indicate small home ranges, or that they preferred dolomitic landscapes due to perhaps cave abundance or factors related to vegetation growth. Similarly, in 2016, Polish anthropologist Katarzyna Kaszycka rebutted that, among primates, delayed maturity is also exhibited in the rhesus monkey which has a multi-male society, and may not be an accurate indicator of social structure. If P. robustus preferred a savanna habitat, a multi-male society would have been more conducive in defending the troop from predators in the more exposed environment, much like baboons which live in the savanna. Even in a multi-male society, it is still possible that males were more likely to be evicted, explaining male-skewed mortality with the same mechanism.
In 2017, anthropologist Katharine Balolia and colleagues postulated that, because male non-human great apes have a larger sagittal crest than females (particularly gorillas and orangutans), the crest may be influenced by sexual selection in addition to supporting chewing muscles. Further, the size of the sagittal crest (and the gluteus muscles) in male western lowland gorillas has been correlated with reproductive success. Balolia et al. extended their interpretation of the crest to the males of Paranthropus species, with the crest and resultantly larger head (at least in P. boisei) being used for some kind of display. This contrasts with other primates which flash the typically enlarged canines in agonistic display (Paranthropus likely did not do this as the canines are comparatively small), though it is also possible that the crest is only so prominent in male gorillas and orangutans because they require larger temporalis muscles to achieve a wider gape to better display the canines. | Paranthropus robustus | Wikipedia | 496 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
Technology
Cave sites in the Cradle of Humankind often have stone and bone tools, with the former attributed to early Homo and the latter generally to P. robustus, as bone tools are most abundant when P. robustus remains far outnumber Homo remains. Australopithecine bone technology was first proposed by Dart in the 1950s with what he termed the "osteodontokeratic culture", which he attributed to A. africanus at Makapansgat dating to 3–2.6 million years ago. These bones are no longer considered to have been tools, and the existence of this culture is not supported. The first probable bone tool was reported by Robinson in 1959 at Sterkfontein Member 5. Excavations led by South African palaeontologist Charles Kimberlin Brain at Swartkrans in the late 1980s and early 1990s recovered 84 similar bone tools, and excavations led by Keyser at Drimolen recovered 23. These tools were all found alongside Acheulean stone tools, except for those from Swartkrans Member 1 which bore Oldowan stone tools. Thus, there are 108 bone tool specimens from the region in total, and possibly an additional two from Kromdraai B. The two stone tools (either "Developed Oldowan" or "Early Acheulean") from Kromdraai B could possibly be attributed to P. robustus, as Homo has not been confidently identified in this layer, though it is possible that the stone tools were reworked (moved into the layer after the inhabitants had died). Bone tools may have been used to cut or process vegetation, process fruits (namely marula fruit), strip tree bark, or dig up tubers or termites. The form of P. robustus incisors appears to be intermediate between H. erectus and modern humans, which could possibly mean it did not have to regularly bite off mouthfuls of a large food item due to preparation with simple tools. The bone tools were typically sourced from the shaft of long bones from medium- to large-sized mammals, but tools sourced from mandibles, ribs, and horn cores have also been found. They were not manufactured or purposefully shaped for a task, but since they display no weathering, and there is a preference displayed for certain bones, raw materials were likely specifically hand picked. This contrasts with East African bone tools which appear to have been modified and directly cut into specific shapes before using. | Paranthropus robustus | Wikipedia | 501 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
In 1988, Brain and South African archaeologist A. Sillent analysed the 59,488 bone fragments from Swartkrans Member 3, and found that 270 had been burnt, mainly belonging to medium-sized antelope, but also zebra, warthog, baboon, and P. robustus. They were found across the entire depth of Member 3, so fire was a regular event throughout its deposition. Based on colour and structural changes, they found that 46 were heated to below , 52 to , 45 to , and 127 above this. They concluded that these bones were, "the earliest direct evidence of fire use in the fossil record," and compared the temperatures with those achieved by experimental campfires burning white stinkwood which commonly grows near the cave. Though some bones had cut marks consistent with butchery, they said it was also possible hominins were making fire to scare away predators or for warmth instead of cooking. Because both P. robustus and H. ergaster/H. erectus were found in the cave, they were unsure which species to attribute the fire to. As an alternative to hominin activity, because the bones were not burnt inside the cave, it is possible that they were naturally burnt in cyclically occurring wildfires (dry savanna grass as well as possible guano or plant accumulation in the cave may have left it susceptible to such a scenario), and then washed into what would become Member 3. The now-earliest claim of fire usage is 1.7 million years ago at Wonderwerk Cave, South Africa, made by South African archaeologist Peter Beaumont in 2011, which he attributed to H. ergaster/H. erectus.
Development | Paranthropus robustus | Wikipedia | 345 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
Australopithecines are generally considered to have had a faster, apelike growth rate than modern humans largely due to dental development trends. Broadly speaking, the emergence of the first permanent molar in early hominins has been variously estimated anywhere from 2.5 to 4.5 years, which all contrast markedly with the modern human average of 5.8 years. The 1st permanent molar of SK 63, which may have died at 3.4–3.7 years of age, possibly erupted at 2.9–3.2 years. In modern apes (including humans), dental development trajectory is strongly correlated with life history and overall growth rate, but it is possible that early hominins simply had a faster dental trajectory but a slower life history due to environmental factors, such as early weaning age as is exemplified in modern indriid lemurs. In TM 1517, fusion of the elements of the distal humerus (at the elbow joint) occurred before the fusion of the elements in the distal big toe phalanx, much like in chimps and bonobos, but unlike humans, which could also indicate an apelike growth trajectory. | Paranthropus robustus | Wikipedia | 238 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
While growing, the front part of the jaw in P. robustus is depository (so it grows) whereas the sides are resorptive (so they recede). For comparison, chimp jaws are generally depository reflecting prognathism, and modern humans resorptive reflecting a flat face. In Paranthropus, this may have functioned to thicken the palate. Unlike other apes and gracile australopithecines, but like humans, the premaxillary suture between the premaxilla and the maxilla (on the palate) formed early in development. At early stages, the P. robustus jawbone was somewhat similar to that of modern humans, but the breadth grew in P. robustus, as to be expected from its incredible robustness in adulthood. By the time the first permanent molar erupts, the body of the mandible and the front jaw broadened, and the ramus of the mandible elongated, diverging from the modern human trajectory. Because the ramus was so tall, it is suggested that P. robustus experienced more anterior face rotation than modern humans and apes. Growth was most marked between the eruptions of the first and second permanent molars, most notably in terms of the distance from the back of the mouth to the front of the mouth, probably to make room for the massive postcanine teeth. Like humans, jaw robustness decreased with age, though it decreased slower in P. robustus. Regardless if P. robustus followed a human or non-human ape dental development timeframe, the premolars and molars would have had an accelerated growth rate to achieve their massive size. In contrast, the presence of perikymata on the incisors and canines (growth lines which typically are worn away after eruption) could indicate these teeth had a reduced growth rate. The tooth roots of P. robustus molars may have grown at a faster rate than gracile australopithecines; the root length of SK 62's 1st molar, which was reaching emergence from the dental alveolus, is about . In contrast, those of other hominins reach after the tooth has emerged not only from the gums (a later stage of dental development). SK 62's growth trajectory is more similar to that of gorillas, whose roots typically measure when emerging from the gums. | Paranthropus robustus | Wikipedia | 496 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
Females may have reached skeletal maturity by the time the third molar erupted, but males appear to have continued growing after reaching dental maturity, during which time they become markedly more robust than females (sexual bimaturism). Similarly, male gorillas complete dental development about the same time as females, but continue growing for up to 5 or 6 years; and male mandrills complete dental development before females, but continue growing for several years more. It is debated whether or not P. robustus had a defined growth spurt in terms of overall height during adolescence, an event unique to humans among modern apes.
Life history
In 1968, American anthropologist Alan Mann, using dental maturity, stratified P. robustus specimens from Swartkrans into different ages, and found an average of 17.2 years at death (they did not necessarily die from old age), and the oldest specimen was 30–35 years old. He also reported an average of 22.2 years for A. africanus. Using these, he argued these hominins had a humanlike prolonged childhood. In response, in 1971, biologist Kelton McKinley repeated Mann's process with more specimens, and (including P. boisei) reported an average of 18 years. McKinley agreed with Mann that P. robustus may have had a prolonged childhood. McKinley also speculated that sexual maturity was reached at approximately 11 years because it is about halfway between the averages for chimps (9 years) and humans (13). Based on this, he concluded babies were birthed at intervals of 3 to 4 years using a statistical test to maximise the number of children born.
In 1972, after estimating a foetal size of based on an adult female weight of , anthropologist Walter Leutenegger estimated foetal head size at about , similar to a chimp. In 1973, using this and an equation between foetal head size and gestation (assuming foetal growth rate of 0.6 for all mammals), biologist John Frazer estimated a gestation of 300 days for P. robustus. In response, Leutenegger pointed out that apes have highly variable foetal growth rates, and "estimates on gestation periods based on this rate and birth weight are useless." | Paranthropus robustus | Wikipedia | 457 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
In 1985, British biologists Paul H. Harvey and Tim Clutton-Brock came up with equations relating body size to life history events for primates, which McHenry applied to australopithecines in 1994. For P. robustus, he reported newborn brain size of 175 cc and weight of , gestation 7.6 months, weaning after 30.1 months of age, maturation age 9.7 years, breeding age 11.4 years, birth interval 45 months, and lifespan 43.3 years. These roughly aligned with other australopithecines and chimps. However, for chimps, he got strongly inaccurate results when compared to actual data for newborn brain size, weaning age, and birth interval, and for humans all metrics except birth interval.
Pathology
Based on a sample of 402 teeth, P. robustus seems to have had a low incidence rate of about 12–16% for tertiary dentin, which forms to repair tooth damage caused by excessive wearing or dental cavities. This is similar to what was found for A. africanus and H. naledi (all three inhabited the Cradle of Humankind at different points in time). In contrast, chimpanzees have an incidence rate of 47%, and gorillas as much as 90%, probably due to a diet with a much higher content of tough plants.
P. robustus seems to have had notably high rates of pitting enamel hypoplasia (PEH), where tooth enamel formation is spotty instead of mostly uniform. In P. robustus, about 47% of baby teeth and 14% of adult teeth were affected, in comparison to about 6.7% and 4.3%, respectively, for the combined teeth of A. africanus, A. sediba, early Homo, and H. naledi. The condition of these holes covering the entire tooth is consistent with the modern human ailment amelogenesis imperfecta. Since circular holes in enamel coverage are uniform in size, only present on the molar teeth, and have the same severity across individuals, the PEH may have been a genetic condition. It is possible that the coding region concerned with thickening enamel also increased the risk of developing PEH. | Paranthropus robustus | Wikipedia | 468 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
As many as four P. robustus individuals have been identified as having had dental cavities, indicating a rate similar to non-agricultural modern humans (1–5%). This is odd as P. robustus is thought to have had a diet high in gritty foods, and gritty foods should decrease cavity incidence rate, so P. robustus may have often consumed high-sugar cavity-causing foods. PEH may have also increased susceptibility to cavities. A molar from Drimolen showed a cavity on the tooth root, a rare occurrence in fossil great apes. In order for cavity-creating bacteria to reach this area, the individual would have also presented either alveolar resportion, which is commonly associated with gum disease; or super-eruption of the tooth which occurs when it becomes worn down and has to erupt a bit more in order to maintain a proper bite, exposing the root in the process. The latter is most likely, and the exposed root seems to have caused hypercementosis to anchor the tooth in place. The cavity seems to have been healing, possibly due to a change in diet or mouth microbiome, or the loss of the adjacent molar.
In a sample of 15 P. robustus specimens, all of them exhibited mild to moderate alveolar bone loss resulting from periodontal disease (the wearing away of the bone which supports the teeth due to gum disease). In contrast, in a sample of 10 A. africanus specimens, three exhibited no pathologies of the alveolar bone. Measuring the distance between the alveolar bone and the cementoenamel junction, P. robustus possibly suffered from a higher rate of tooth-attachment loss, unless P. robustus had a higher cervical height (the slightly narrowed area where the crown meets the root) in which case these two species had the same rate of tooth-attachment loss. If the former is correct, then the difference may be due to different dietary habits, chewing strategies, more pathogenic mouth microflora in P. robustus, or some immunological difference which made P. robustus somewhat more susceptible to gum disease. | Paranthropus robustus | Wikipedia | 444 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
While removing the matrix encapsulating TM 1517, Schepers noted a large rock, which would have weighed , which had driven itself into the braincase through the parietal bone. He considered this evidence that another individual had killed TM 1517 by launching the rock as a projectile in either defense or attack, but the most parsimonious explanation is that the rock was deposited during the fossilisation process after TM 1517 had died. In 1961, science writer Robert Ardrey noted two small holes about 2.5 cm (an inch) apart on the child skullcap SK 54, and believed this individual had been killed by being struck twice on the head in an assault; in 1970, Brain reinterpreted this as evidence of a leopard attack.
Palaeoecology
The Pleistocene Cradle of Humankind was mainly dominated by the springbok Antidorcas recki, but other antelope, giraffes, and elephants were also seemingly abundant megafauna. The carnivore assemblage comprises the sabertoothed cats Dinofelis spp. and Megantereon spp., and the hyena Lycyaenops silberbergi. Overall, the animal assemblage of the region broadly indicates a mixed, open-to-closed landscape featuring perhaps montane grasslands and shrublands. Australopithecines and early Homo likely preferred cooler conditions than later Homo, as there are no australopithecine sites that were below in elevation at the time of deposition. This would mean that, like chimps, they often inhabited areas with an average diurnal temperature of , dropping to at night. | Paranthropus robustus | Wikipedia | 344 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
P. robustus also cohabited the Cradle of Humankind with H. ergaster/H. erectus. In addition, these two species resided alongside Australopithecus sediba which is known from about 2 million years ago at Malapa. The most recent A. africanus specimen, Sts 5, dates to about 2.07 million years ago, around the arrival of P. robustus and H. erectus. It has been debated whether or not P. robustus would have had symbiotic, neutral, or antagonist relations with contemporary Australopithecus and Homo. It is possible that South Africa was a refugium for Australopithecus until about 2 million years ago with the beginning of major climatic variability and volatility, and potentially competition with Homo and Paranthropus.
Fossil-bearing deposits
Swartkrans
At Swartkrans, P. robustus has been identified from Members 1–3. Homo is also found in these deposits, but species identification in Members 1 and 2 is debated between H. ergaster/H. erectus, H. habilis, H. rudolfensis, or multiple species. In total, over 300 P. robustus specimens representing over 130 individuals, predominantly isolated teeth, have been recovered from Swartkrans.
Member 1 and Member 3 have several mammal species in common, making dating by animal remains (biostratigraphy) yield overlapping time intervals. Like the East African Olduvai Bed I (2.03–1.75 million years ago) and Lower Bed II (1.75–1.70 million years ago), Member 1 preserved the antelope Parmularius angusticornis, the wildebeest, and the Cape buffalo. The presence of the Hamadryas baboon and Dinopithecus could mean Members 1–3 were deposited 1.9–1.65 million years ago, though the presence of warthogs suggests some sections of the deposits could date to after 1.5 million years ago. Uranium–lead dating reports intervals of 3.21–0.45 million years ago for Member 1 (a very large error range), 1.65–1.07 million years ago for Member 2, and 1.04–0.62 million years ago for Member 3, though more likely the younger side of the estimate; this could mean P. robustus outlived P. boisei. | Paranthropus robustus | Wikipedia | 507 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
Cosmogenic nuclide geochronology has reported much more constrained dates of 2.2–1.8 million years ago for Member 1, and 0.96 million years ago for Member 3. No suitable section of Member 2 could be identified to date.
Sterkfontein
At Sterkfontein, only the specimens StW 566 and StW 569 are firmly assigned to P. robustus, coming from the "Oldowan infill" dating to 2–1.7 million years ago in a section of Member 5. Earlier members yielded A. africanus. In 1988, palaeoanthropologist Ronald J. Clarke suggested StW 505 from the earlier Member 4 was an ancestor to P. robustus. The specimen is still generally assigned to A. africanus, though the Sterkfontein hominins are known to have an exceedingly wide range of variation, and it is debated whether or not the materials represent multiple species instead of just A. africanus.
The appearance of the baboon Theropithecus oswaldi, zebras, lions, ostriches, springhares, and several grazing antelope in Member 5 indicates the predominance of open grasslands, but sediment analysis indicates the cave opening was moist during deposition, which could point to a well-watered wooded grassland.
Kromdraai
At Kromdraai, P. robustus has been unearthed at Kromdraai B, and almost all P. robustus fossils discovered in the cave have been recovered from Member 3 (out of 5 members). A total of 31 specimens representing at least 17 individuals have been recovered. The only potential Homo specimen from Member 3 is KB 5223, but its classification is debated. The ear bones of the juvenile KB 6067 from Member 3 is consistent with that of P. robustus, but the dimensions of the cochlea and oval window better align with the more ancient StW 53 from Sterkfontein Member 4 with undetermined species designation. KB 6067, therefore, may possibly be basal to (more ancient than) other P. robustus specimens, at least those for which ear morphology is known.
Palaeomagnetism suggests Member 3 may date to 1.78–1.6 million years ago, Member 2 to before 1.78 million years ago, and Member 1 to 2.11–1.95 million years ago. | Paranthropus robustus | Wikipedia | 501 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
The animal remains of Kromdraai A suggest deposition occurred anywhere between 1.89 and 1.63 million years ago, and the presence of Oldowan or Achulean tools indicates early Homo activity. The biostratigraphic dating of Kromdraai B is less clear as there are no animal species which are known to have existed in a narrow time interval, and many non-hominin specimens have not been assigned to a species (left at genus level). About 75% of mammalian remains other than P. robustus are monkeys, including leaf-eating colobine monkeys, possibly the earliest record of the Hamadryas baboon, Gorgopithecus, and Papio angusticeps in South Africa. The absence of the baboons T. oswaldi and Dinopithecus could potentially mean Member 3 is older than Sterkfontein Member 5 and Swartkrans Member 1; which, if correct, would invalidate the results from palaeomagnetism, and make these specimens among the oldest representatives of the species.
Gondolin Cave
Gondolin Cave has yielded 3 hominin specimens: a right third premolar assigned to early Homo (G14018), a partial left gracile australopithecine first or second molar (GDA-1), and a robust australopithecine second molar (GDA-2). The first hominin specimen (G14018) was found by German palaeontologist Elisabeth Vrba in 1979, and the other two specimens were recovered in 1997 by, respectively, South African palaeoanthropologist Andre Keyser and excavator L. Dihasu. GDA-2—measuring , an area of —is exceptionally large for P. robustus, which has a recorded maximum of . This falls within the range of P. boisei , so the discoverers assigned it to an indeterminate species of Paranthropus rather than P. robustus.
GDA-2 was found alongside the pig Metridiochoerus andrewsi, which means the tooth must be 1.9–1.5 million years old. Using this and palaeomagnetism, it may date to roughly 1.8 million years ago. | Paranthropus robustus | Wikipedia | 474 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
Cooper's Cave
Cooper's Cave was first reported to yield P. robustus remains in 2000 by South African palaeoanthropologists Christine Steininger and Lee Rogers Berger. Specimens include a crushed partial right face (COB 101), three isolated teeth, a juvenile jawbone, and several skull fragments.
The animal remains in the hominin-bearing deposit are similar to those of Swartkrans and Kromdraai A, so the Cooper's Cave deposits may date to 1.87–1.56 million years ago.
Drimolen Cave
Drimolen Cave was first discovered to have yielded hominin remains by Keyser in 1992, who, in eight years, oversaw the recovery of 79 P. robustus specimens. Among these are the most complete P. robustus skulls: the presumed female DNH-7 (which also preserved articulated jawbone with almost all the teeth), and presumed male DNH 155. It was also associated with the H. ergaster/H. erectus skull DNH 134. The Drimolen material preserves several basal characteristics relative to the Swartkrans and Kromdraai remains (meaning it may be older).
The site is thought to be roughly 2–1.5 million years old based on animal remains which have also been recovered from Swartkrans Member 1. The animal assemblage is broadly similar to that of Cooper's Cave, meaning they probably are about the same age. In 2020, DNH 152 was palaeomagnetically dated to 2.04–1.95 million years ago, making it the oldest identified P. robustus specimen.
Predation | Paranthropus robustus | Wikipedia | 341 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
Australopithecine bones may have accumulated in caves due to large carnivores dragging in carcasses, which was first explored in detail by Brain in his 1981 book The Hunters or the Hunted?: An Introduction to African Cave Taphonomy. The juvenile P. robustus skullcap SK 54 has two puncture marks consistent with the lower canines of the leopard specimen SK 349 from the same deposits. Brain hypothesised that Dinofelis and perhaps also hunting hyenas specialised on killing australopithecines, but carbon isotope analysis indicates these species predominantly ate large grazers, while the leopard, the sabertoothed Megantereon, and the spotted hyena were more likely to have regularly consumed P. robustus. Brain was unsure if these predators actively sought them out and brought them back to the cave den to eat, or inhabited deeper recesses of caves and ambushed them when they entered. Modern-day baboons in this region often shelter in sinkholes especially on cold winter nights, though Brain proposed that australopithecines seasonally migrated out of the Highveld and into the warmer Bushveld, only taking up cave shelters in spring and autumn.
As an antipredator behaviour, baboons often associate themselves with medium-to-large herbivores, most notably impalas, and it is possible that P. robustus as well as other early hominins which lived in open environments did so also, given they are typically associated with an abundance of medium-to-large bovid and horse remains. | Paranthropus robustus | Wikipedia | 321 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
Extinction
Though P. robustus was a rather hardy species with a tolerance for environmental variability, it seems to have preferred wooded environments, and similarly most P. robustus remains date to a wet period in South Africa 2–1.75 million years ago conducive to such biomes. The extinction of P. robustus coincided with the Mid-Pleistocene Transition, and the doubling of glacial cycle duration. During glacial events, with more ice locked up at the poles, the tropical rain belt contracted towards the equator, subsequently causing the retreat of wetland and woodland environments. Before the transition, P. robustus populations possibly contracted to certain wooded refuge zones over 21,000-year cycles, becoming regionally extinct in certain areas until the wet cycle whereupon it would repopulate those zones. The continual prolonging of dry cycles may have caused its extinction, with the last occurrence in the fossil record 1–0.6 million years ago (though more likely 0.9 million years ago). Homo possibly was able to survive by inhabiting a much larger geographical range, more likely to find a suitable refuge area during unfavourable climate swings.
However, the geographical range of P. robustus in the fossil record is roughly , whereas the critically endangered eastern gorilla (with the smallest range of any African ape) inhabits , the critically endangered western gorilla , and the endangered chimpanzee . Therefore, fossil distribution very unlikely represents the true range of the species; consequently, P. robustus possibly went extinct much more recently somewhere other than the Cradle of Humankind (Signor–Lipps effect). | Paranthropus robustus | Wikipedia | 324 | 2165269 | https://en.wikipedia.org/wiki/Paranthropus%20robustus | Biology and health sciences | Australopithecines | Biology |
Paranthropus boisei is a species of australopithecine from the Early Pleistocene of East Africa about 2.5 to 1.15 million years ago. The holotype specimen, OH 5, was discovered by palaeoanthropologist Mary Leakey in 1959 at Olduvai Gorge, Tanzania and described by her husband Louis a month later. It was originally placed into its own genus as "Zinjanthropus boisei", but is now relegated to Paranthropus along with other robust australopithecines. However, it is also argued that Paranthropus is an invalid grouping and synonymous with Australopithecus, so the species is also often classified as Australopithecus boisei.
Robust australopithecines are characterised by heavily built skulls capable of producing high stresses and bite forces, and some of the largest molars with the thickest enamel of any known ape. P. boisei is the most robust of this group. Brain size was about , similar to other australopithecines. Some skulls are markedly smaller than others, which is taken as evidence of sexual dimorphism where females are much smaller than males, though body size is difficult to estimate given only one specimen, OH 80, definitely provides any bodily elements. The presumed male OH 80 may have been tall and in weight, and the presumed female KNM-ER 1500 tall (though its species designation is unclear). The arm and hand bones of OH 80 and KNM-ER 47000 suggest P. boisei was arboreal to a degree. | Paranthropus boisei | Wikipedia | 332 | 2165275 | https://en.wikipedia.org/wiki/Paranthropus%20boisei | Biology and health sciences | Australopithecines | Biology |
P. boisei was originally believed to have been a specialist species of hard foods, such as nuts, due to its heavily built skull, but it was more likely a generalist feeder of predominantly abrasive C4 plants, such as grasses or underground storage organs. Like gorillas, the apparently specialised adaptations of the skull may have only been used with less desirable fallback foods, allowing P. boisei to inhabit a wider range of habitats than gracile australopithecines. P. boisei may have been able to make Oldowan stone tools and butcher carcasses. P. boisei mainly inhabited wet, wooded environments, and coexisted with H. habilis, H. rudolfensis and H. ergaster/erectus. These were likely preyed upon by the large carnivores of the time, including big cats, crocodiles and hyenas.
Research history
Discovery
Palaeoanthropologists Mary and Louis Leakey had conducted excavations in Tanzania since the 1930s, though work was postponed with the start of World War II. They returned in 1951, finding mostly ancient tools and fossils of extinct mammals for the next few years. In 1955, they unearthed a hominin baby canine and large molar tooth in Olduvai Gorge, catalogue ID Olduvai Hominin (OH) 3.
On the morning of July 17, 1959, Louis felt ill and stayed at camp while Mary went out to Bed I's Frida Leakey Gully. Sometime around 11:00 AM, she noticed what appeared to be a portion of a skull poking out of the ground, OH 5. The dig team created a pile of stones around the exposed portion to protect it from further weathering. Active excavation began the following day; they had chosen to wait for photographer Des Bartlett to document the entire process. The partial cranium was fully unearthed August 6, though it had to be reconstructed from its fragments which were scattered in the scree. Louis published a short summary of the find and context the following week. | Paranthropus boisei | Wikipedia | 420 | 2165275 | https://en.wikipedia.org/wiki/Paranthropus%20boisei | Biology and health sciences | Australopithecines | Biology |
Louis determined OH 5 to be a subadult or adolescent based on dental development, and he and Mary nicknamed it "Dear Boy". After they reconstructed the skull and jaws, newspapers began referring to it as "Nutcracker Man" due to the large back teeth and jaws which gave it a resemblance to vintage nutcrackers. South African palaeoanthropologist Phillip Tobias, a colleague of the Leakeys, has also received attribution for this nickname. The cranium was taken to Kenya after its discovery and was there until January 1965 when it was placed on display in the Hall of Man at the National Museum of Tanzania in Dar es Salaam.
Other specimens
Louis preliminarily supposed OH 5 was about half a million years old, but in 1965, American geologists Garniss Curtis and Jack Evernden dated OH 5 to 1.75 million years ago using potassium–argon dating of anortoclase crystals from an overlying tuff (volcanic ash) bed. Such an application of geochronology was unprecedented at the time. | Paranthropus boisei | Wikipedia | 220 | 2165275 | https://en.wikipedia.org/wiki/Paranthropus%20boisei | Biology and health sciences | Australopithecines | Biology |
The first identified jawbone, Peninj 1, was discovered Lake Natron just north of Olduvai Gorge in 1964. Especially from 1966 to 1975, several more specimens revealing facial elements were reported from the Shungura Formation, Ethiopia; Koobi Fora and Chesowanja, Kenya; and Omo and Konso, Ethiopia. Among the notable specimens found include the well preserved skull KNM-ER 406 from Koobi Fora in 1970. In 1997, the first specimen with both the skull and jawbone (and also one of the largest specimens), KGA10-525, was discovered in Konso. In 1999, a jawbone was recovered from Malema, Malawi, extending the species' southernmost range over from Olduvai Gorge. The first definitive bodily elements of P. boisei associated with facial elements, OH 80 (isolated teeth with an arm and a leg), were discovered in 2013. Previously, body remains lacking unambiguous diagnostic skull elements had been dubiously assigned to the species, namely the partial skeleton KNM-ER 1500 associated with a small jawbone fragment. In 2015, based on OH 80, American palaeoanthropologist Michael Lague recommended assigning the isolated humerus specimens KNM-ER 739, 1504, 6020 and 1591 from Koobi Fora to P. boisei. In 2020, the first associated hand bones were reported, KNM-ER 47000 (which also includes a nearly complete arm), from Ileret, Kenya.
Naming
The remains were clearly australopithecine (not of the genus Homo), and at the time, the only australopithecine genera described were Australopithecus by Raymond Dart and Paranthropus (the South African P. robustus) by Robert Broom, and there were arguments that Paranthropus was synonymous with Australopithecus. Louis believed the skull had a mix of traits from both genera, briefly listing 20 differences, and so used OH 5 as the basis for the new genus and species "Zinjanthropus boisei" on August 15, 1959. The genus name derives from the medieval term for East Africa, "Zanj", and the specific name was in honour of Charles Watson Boise, the Leakeys' benefactor. He initially considered the name "Titanohomo mirabilis" ("wonderful Titan-like man"). | Paranthropus boisei | Wikipedia | 507 | 2165275 | https://en.wikipedia.org/wiki/Paranthropus%20boisei | Biology and health sciences | Australopithecines | Biology |
Soon after, Louis presented "Z." boisei to the 4th Pan-African Congress on Prehistory in Léopoldville, Belgian Congo (now Kinshasa, Democratic Republic of the Congo). Dart made his now famous joke, "... what would have happened if [the A. africanus specimen] Mrs. Ples had met Dear Boy one dark night." At the time of discovery, there was resistance to erecting completely new genera based on single specimens, and the Congress largely rejected "Zinjanthropus". In 1960, American anthropologist John Talbot Robinson pointed out that the supposed differences between "Zinjanthropus" and Paranthropus are due to OH 5 being slightly larger, and so recommended the species be reclassified as P. boisei. Louis rejected Robinson's proposal. Following this, it was debated if P. boisei was simply an East African variant of P. robustus until 1967 when South African palaeoanthropologist Phillip V. Tobias gave a far more detailed description of OH 5 in a monograph (edited by Louis). Tobias and Louis still retained "Zinjanthropus", but recommended demoting it to subgenus level as Australopithecus ("Zinjanthropus") boisei, considering Paranthropus to be synonymous with Australopithecus. Synonymising Paranthropus with Australopithecus was first suggested by anthropologists Sherwood Washburn and Bruce D. Patterson in 1951, who recommended limiting hominin genera to only Australopithecus and Homo.
Classification | Paranthropus boisei | Wikipedia | 333 | 2165275 | https://en.wikipedia.org/wiki/Paranthropus%20boisei | Biology and health sciences | Australopithecines | Biology |
The genus Paranthropus (otherwise known as "robust australopithecines") typically includes P. boisei, P. aethiopicus and P. robustus. It is debated if Paranthropus is a valid natural grouping (monophyletic) or an invalid grouping of similar-looking hominins (paraphyletic). Because skeletal elements are so limited in these species, their affinities with each other and to other australopithecines is difficult to gauge with accuracy. The jaws are the main argument for monophyly, but such anatomy is strongly influenced by diet and environment, and could in all likelihood have evolved independently in P. boisei and P. robustus. Proponents of monophyly consider P. aethiopicus to be ancestral to the other two species, or closely related to the ancestor. Proponents of paraphyly allocate these three species to the genus Australopithecus as A. boisei, A. aethiopicus and A. robustus. | Paranthropus boisei | Wikipedia | 216 | 2165275 | https://en.wikipedia.org/wiki/Paranthropus%20boisei | Biology and health sciences | Australopithecines | Biology |
Before P. boisei was described (and P. robustus was the only member of Paranthropus), Broom and Robinson continued arguing that P. robustus and A. africanus (the then only known australopithecines) were two distinct lineages. However, remains were not firmly dated, and it was debated if there were indeed multiple hominin lineages or if there was only 1 leading to humans. In 1975, the P. boisei skull KNM-ER 406 was demonstrated to have been contemporaneous with the H. ergaster/erectus skull KNM ER 3733, which is generally taken to show that Paranthropus was a sister taxon to Homo, both developing from some Australopithecus species, which at the time only included A. africanus. In 1979, a year after describing A. afarensis from East Africa, anthropologists Donald Johanson and Tim D. White suggested that A. afarensis was instead the last common ancestor between Homo and Paranthropus, and A. africanus was the earliest member of the Paranthropus lineage or at least was ancestral to P. robustus, because A. africanus inhabited South Africa before P. robustus, and A. afarensis was at the time the oldest-known hominin species at roughly 3.5 million years old. Now, the earliest known South African australopithecine ("Little Foot") dates to 3.67 million years ago, contemporaneous with A. afarensis.
Such arguments are based on how one draws the hominin family tree, and the exact classification of Australopithecus species with each other is quite contentious. For example, if the South African A. sediba (which evolved from A. africanus) is considered the ancestor or closely related to the ancestor of Homo, then this could allow for A. africanus to be placed more closely related to Homo than to Paranthropus. This would leave the Ethiopian A. garhi as the ancestor of P. aethiopicus instead of A. africanus (assuming Paranthropus is monophyletic, and that P. aethiopicus evolved at a time in East Africa when only A. garhi existed there). | Paranthropus boisei | Wikipedia | 476 | 2165275 | https://en.wikipedia.org/wiki/Paranthropus%20boisei | Biology and health sciences | Australopithecines | Biology |
Because P. boisei and P. aethiopicus are both known from East Africa and P. aethiopicus is only confidently identified from the skull KNM WT 17000 and a few jaws and isolated teeth, it is debated if P. aethiopicus should be subsumed under P. boisei or if the differences stemming from archaicness justifies species distinction. The terms P. boisei sensu lato ("in the broad sense") and P. boisei sensu stricto ("in the strict sense") can be used to respectively include and exclude P. aethiopicus from P. boisei when discussing the lineage as a whole.
P. aethiopicus is the earliest member of the genus, with the oldest remains, from the Ethiopian Omo Kibish Formation, dated to 2.6 million years ago (mya) at the end of the Pliocene. It is possible that P. aethiopicus evolved even earlier, up to 3.3 mya, on the expansive Kenyan floodplains of the time. The oldest P. boisei remains date to about 2.3 mya from Malema. The youngest record of P. boisei comes Olduvai Gorge (OH 80) about 1.34 mya; however, due a large gap in the hominin fossil record, P. boisei may have persisted until 1 mya. P. boisei changed remarkably little over its nearly one-million-year existence.
Anatomy
Skull | Paranthropus boisei | Wikipedia | 313 | 2165275 | https://en.wikipedia.org/wiki/Paranthropus%20boisei | Biology and health sciences | Australopithecines | Biology |
P. boisei is the most robust of the robust australopithecines, whereas the South African P. robustus is smaller with comparatively more gracile features. The P. boisei skull is heavily built, and features a defined brow ridge, receding forehead, rounded bottom margins of the eye sockets, inflated and concave cheek bones, a thick palate, and a robust and deep jawbone. This is generally interpreted as having allowed P. boisei to resist high stresses while chewing, though the thick palate could instead be a byproduct of facial lengthening. The skull features large rough patches (rugosities) on the cheek and jawbones, and males have pronounced sagittal (on the midline) and temporonuchal (on the back) crests, which indicate a massive masseter muscle (used in biting down) placed near the front of the head (increasing mechanical advantage). This is typically considered to be evidence of a high bite force.
The incisors and canines are reduced, which would hinder biting off chunks of large food pieces. In contrast, the cheek teeth of both sexes are enormous (postcanine megadontia), and the greater surface area would have permitted the processing of larger quantities of food at once. In the upper jaw, the 1st molar averages roughly , the 2nd molar , and the 3rd molar ; in the lower jaw, the 1st molar averages roughly , the 2nd molar , and the 3rd molar . The molars are bunodont, featuring low and rounded cusps. The premolars resemble molars (are molarised), which may indicate P. boisei required an extended chewing surface for processing a lot of food at the same time. The enamel on the cheek teeth are among the thickest of any known ape, which would help resist high stresses while biting.
Brain and sinuses
In a sample of 10 P. boisei specimens, brain size varied from with an average of . However, the lower-end specimen, Omo L338‐y6, is a juvenile, and many skull specimens have a highly damaged or missing frontal bone which can alter brain volume estimates. The brain volume of australopithecines generally ranged from , and for contemporary Homo . | Paranthropus boisei | Wikipedia | 472 | 2165275 | https://en.wikipedia.org/wiki/Paranthropus%20boisei | Biology and health sciences | Australopithecines | Biology |
Regarding the dural venous sinuses, in 1983, American neuroanthropologist Dean Falk and anthropologist Glenn Conroy suggested that, unlike A. africanus or modern humans, all Paranthropus (and A. afarensis) had expanded occipital and marginal (around the foramen magnum) sinuses, completely supplanting the transverse and sigmoid sinuses. In 1988, Falk and Tobias demonstrated that hominins can have both an occipital/marginal and transverse/sigmoid systems concurrently or on opposite halves of the skull, such as with the P. boisei specimen KNM-ER 23000.
In 1983, French anthropologist Roger Saban stated that the parietal branch of the middle meningeal artery originated from the posterior branch in P. boisei and P. robustus instead of the anterior branch as in earlier hominins, and considered this a derived characteristic due to increased brain capacity. It has since been demonstrated that the parietal branch could originate from either the anterior or posterior branches, sometimes both in a single specimen on opposite sides of the skull as in KNM-ER 23000 and OH 5.
Postcranium
The wide range of size variation in skull specimens seems to indicate a great degree of sexual dimorphism with males being notably bigger than females. However, it is difficult to predict with accuracy the true dimensions of living males and females due to the lack of definitive P. boisei skeletal remains, save for the presumed male OH 80. Based on an approximation of for the femur before it was broken and using modern humanlike proportions (which is probably an unsafe assumption), OH 80 was about tall in life. For comparison, modern human men and women in the year 1900 averaged and , respectively. The femoral head, the best proxy for estimating body mass, is missing, but using the shaft, OH 80 weighed about assuming humanlike proportions, and using the proportions of a non-human ape. The ambiguously attributed, presumed female femur KNM-ER 1500 is estimated to have been of an individual about tall which would be consistent with the argument of sexual dimorphism, but if the specimen does indeed belong to P. boisei, it would show a limb anatomy quite similar to that of the contemporary H. habilis. | Paranthropus boisei | Wikipedia | 478 | 2165275 | https://en.wikipedia.org/wiki/Paranthropus%20boisei | Biology and health sciences | Australopithecines | Biology |
Instead, the OH 80 femur, more like H. erectus femora, is quite thick, features a laterally flattened shaft, and indicates similarly arranged gluteal, pectineal and intertrochanteric lines around the hip joint. Nonetheless, the intertrochanteric line is much more defined in OH 80, the gluteal tuberosity is more towards the midline of the femur, and the mid-shaft in side-view is straighter, which likely reflect some difference in load-bearing capabilities of the leg. Unlike P. robustus, the arm bones of OH 80 are heavily built, and the elbow joint shows similarities to that of modern gibbons and orangutans. This could either indicate that P. boisei used a combination of terrestrial walking as well as suspensory behaviour, or was completely bipedal but retained an ape-like upper body condition from some ancestor species due to a lack of selective pressure to lose them. In contrast, the P. robustus hand is not consistent with climbing. The hand of KNM-ER 47000 shows Australopithecus-like anatomy lacking the third metacarpal styloid process (which allows the hand to lock into the wrist to exert more pressure), a weak thumb compared to modern humans, and curved phalanges (finger bones) which are typically interpreted as adaptations for climbing. Nonetheless, despite lacking a particularly forceful precision grip like Homo, the hand was still dextrous enough to handle and manufacture simple tools.
Palaeobiology
Diet
In 1954, Robinson suggested that the heavily built skull of Paranthropus (at the time only including P. robustus) was indicative of a specialist diet specifically adapted for processing a narrow band of foods. Because of this, the predominant model of Paranthropus extinction for the latter half of the 20th century was that it was unable to adapt to the volatile climate of the Pleistocene, unlike the much more adaptable Homo. It was also once thought P. boisei cracked open nuts and similar hard foods with its powerful teeth, giving OH 5 the nickname "Nutcracker Man". | Paranthropus boisei | Wikipedia | 442 | 2165275 | https://en.wikipedia.org/wiki/Paranthropus%20boisei | Biology and health sciences | Australopithecines | Biology |
However, in 1981, English anthropologist Alan Walker found that the microwearing patterns on the molars were inconsistent with a diet high in hard foods, and were effectively indistinguishable from the pattern seen in the molars of fruit-eating (frugivorous) mandrills, chimpanzees and orangutans. The microwearing on P. boisei molars is different from that on P. robustus molars, and indicates that P. boisei, unlike P. robustus, very rarely ever ate hard foods. Carbon isotope analyses report a diet of predominantly C4 plants, such as low quality and abrasive grasses and sedges. Thick enamel is consistent with grinding abrasive foods. The microwear patterns in P. robustus have been thoroughly examined, and suggest that the heavy build of the skull was only relevant when eating less desirable fallback foods. A similar scheme may have been in use by P. boisei. Such a strategy is similar to that used by modern gorillas, which can sustain themselves entirely on lower quality fallback foods year-round, as opposed to lighter built chimps (and presumably gracile australopithecines) which require steady access to high quality foods.
In 1980, anthropologists Tom Hatley and John Kappelman suggested that early hominins (convergently with bears and pigs) adapted to eating abrasive and calorie-rich underground storage organs (USOs), such as roots and tubers. Since then, hominin exploitation of USOs has gained more support. In 2005, biological anthropologists Greg Laden and Richard Wrangham proposed that Paranthropus relied on USOs as a fallback or possibly primary food source, and noted that there may be a correlation between high USO abundance and hominin occupation. In this model, P. boisei may have been a generalist feeder with a predilection for USOs, and may have gone extinct due to an aridity trend and a resultant decline in USOs in tandem with increasing competition with baboons and Homo. Like modern chimps and baboons, australopithecines likely foraged for food in the cooler morning and evening instead of in the heat of the day. | Paranthropus boisei | Wikipedia | 470 | 2165275 | https://en.wikipedia.org/wiki/Paranthropus%20boisei | Biology and health sciences | Australopithecines | Biology |
Technology
By the time OH 5 was discovered, the Leakeys had spent 24 years excavating the area for early hominin remains, but had instead recovered mainly other animal remains as well as the Oldowan stone tool industry. Because OH 5 was associated with the tools and processed animal bones, they presumed it was the toolmaker. Attribution of the tools was promptly switched to the bigger-brained H. habilis upon its description in 1964. In 2013, OH 80 was found associated with a mass of Oldowan stone tools and animal bones bearing evidence of butchery. This could potentially indicate P. boisei was manufacturing this industry and ate meat to some degree.
Additionally, the Early Stone Age of Africa coincides with simple bone tools. In South Africa, these are unearthed in the Cradle of Humankind and are largely attributed to P. robustus. In East Africa, a few have been encountered at Olduvai Gorge Beds I–IV, occurring over roughly 1.7 to 0.8 million years ago, and are usually made of limb bones and possibly teeth of large mammals, most notably elephants. The infrequency of such large animals at this site may explain the relative rarity of bone tools. The toolmakers were modifying bone in much the same way as they did with stone. Though the Olduvan bone tools are normally ascribed to H. ergaster/erectus, the presence of both P. boisei and H. habilis obfuscates attribution. | Paranthropus boisei | Wikipedia | 310 | 2165275 | https://en.wikipedia.org/wiki/Paranthropus%20boisei | Biology and health sciences | Australopithecines | Biology |
Social structure
In 1979, American biological anthropologist Noel T. Boaz noticed that the relative proportions between large mammal families at the Shungura Formation are quite similar to the proportion in modern-day across sub-Saharan Africa. Boaz believed that hominins would have had about the same population density as other large mammals, which would equate to 0.006–1.7 individuals per square kilometre (0.4 square mile). Alternatively, by multiplying the density of either bovids, elephants, or hippos by the percentage of hominin remains out of total mammal remains found at the formation, Boaz estimated a density of 0.001–2.58 individuals per square kilometre. Biologist Robert A. Martin considered population models based on the number of known specimens to be flimsy. In 1981, Martin applied equations formulated by ecologists Alton S. Harestad and Fred L. Bunnel in 1979 to estimate the home range and population density of large mammals based on weight and diet, and, using a weight of , he got: and 0.769 individual per square kilometre if herbivorous; and 0.077 individual if omnivorous; and and 0.0004 individual if carnivorous. For comparison, he calculated and 0.104 individual per square kilometre for omnivorous, chimps.
A 2017 study postulated that, because male non-human great apes have a larger sagittal crest than females (particularly gorillas and orangutans), the crest may be influenced by sexual selection in addition to supporting chewing muscles. Further, the size of the sagittal crest (and the gluteus muscles) in male western lowland gorillas has been correlated with reproductive success. They extended their interpretation of the crest to the males of Paranthropus species, with the crest and resultantly larger head (at least in P. boisei) being used for some kind of display. This contrasts with other primates which flash the typically engorged canines in agonistic display (the canines of Paranthropus are comparatively small). However, it is also possible that male gorillas and orangutans require larger temporalis muscles to achieve a wider gape to better display the canines. | Paranthropus boisei | Wikipedia | 462 | 2165275 | https://en.wikipedia.org/wiki/Paranthropus%20boisei | Biology and health sciences | Australopithecines | Biology |
Development
Australopithecines are generally considered to have had a faster, apelike growth rate than modern humans largely due to dental development trends. Broadly speaking, the emergence of the first permanent molar in early hominins has been variously estimated anywhere from 2.5 to 4.5 years of age, which all contrast markedly with the modern human average of 5.8 years. The tips of the mesial cusps of the 1st molar (on the side closest to the premolar) of KNM-ER 1820 were at about the same level as the cervix (where the enamel meets the cementum) of its non-permanent 2nd premolar. In baboons, this stage occurs when the 1st molar is about to erupt from the gums. The tooth root is about , which is similar to most other hominins at this stage. In contrast, the root of the P. robustus specimen SK 62 was when emerging through the dental alveolus (an earlier stage of development than gum emergence), so, unless either specimen is abnormal, P. robustus may have had a higher tooth-root formation rate. The specimen's 1st molar may have erupted 2–3 months before death, so possibly at 2.7–3.3 years of age. In modern apes (including humans), dental development trajectory is strongly correlated with life history and overall growth rate, but it is possible that early hominins simply had a faster dental trajectory and slower life history due to environmental factors, such as early weaning age exhibited in modern indriid lemurs. | Paranthropus boisei | Wikipedia | 333 | 2165275 | https://en.wikipedia.org/wiki/Paranthropus%20boisei | Biology and health sciences | Australopithecines | Biology |
Palaeoecology
P. boisei remains have been found predominantly in what were wet, wooded environments, such as wetlands along lakes and rivers, wooded or arid shrublands, and semi-arid woodlands, with the exception of the savanna-dominated Malawian Chiwondo Beds. Its abundance likely increased during precession-driven periods of relative humidity while being more rare during intervals of aridity. During the Pleistocene, there seems to have been coastal and montane forests in Eastern Africa. More expansive river valleys–namely the Omo River Valley–may have served as important refuges for forest-dwelling creatures. Being cut off from the forests of Central Africa by a savanna corridor, these East African forests would have promoted high rates of endemism, especially during times of climatic volatility. Australopithecines and early Homo likely preferred cooler conditions than later Homo, as there are no australopithecine sites that were below in elevation at the time of deposition. This would mean that, like chimps, they often inhabited areas with an average diurnal temperature of , dropping to at night.
P. boisei coexisted with H. habilis, H. rudolfensis and H. ergaster/erectus, but it is unclear how they interacted. To explain why P. boisei was associated with Oldowan tools despite not being the tool maker, Louis Leakey and colleagues, when describing H. habilis in 1964, suggested that one possibility was P. boisei was killed by H. habilis, perhaps as food. However, when describing P. boisei 5 years earlier, he said, "There is no reason whatever, in this case, to believe that the skull [OH 5] represents the victim of a cannibalistic feast by some hypothetical more advanced type of man." OH 80 seems to have been eaten by a big cat. The leg OH 35, which either belongs to P. boisei or H. habilis, shows evidence of leopard predation. Other likely Oldowan predators of great apes include the hunting hyena Chasmaporthetes nitidula, the sabertoothed cats Dinofelis and Megantereon, and the crocodile Crocodylus anthropophagus. | Paranthropus boisei | Wikipedia | 463 | 2165275 | https://en.wikipedia.org/wiki/Paranthropus%20boisei | Biology and health sciences | Australopithecines | Biology |
Traditional Japanese units of measurement or the shakkanhō () is the traditional system of measurement used by the people of the Japanese archipelago. It is largely based on the Chinese system, which spread to Japan and the rest of the Sinosphere in antiquity. It has remained mostly unaltered since the adoption of the measures of the Tang dynasty in 701. Following the 1868 Meiji Restoration, Imperial Japan adopted the metric system and defined the traditional units in metric terms on the basis of a prototype metre and kilogram. The present values of most Korean and Taiwanese units of measurement derive from these values as well.
For a time in the early 20th century, the traditional, metric, and English systems were all legal in Japan. Although commerce has since been legally restricted to using the metric system, the old system is still used in some instances. The old measures are common in carpentry and agriculture, with tools such as chisels, spatels, saws, and hammers manufactured in sun and bu sizes. Floorspace is expressed in terms of tatami mats, and land is sold on the basis of price in tsubo. Sake is sold in multiples of 1gō, with the most common bottle sizes being 4 (720 mL) or 10 (1.8 L, isshōbin).
History
Customary Japanese units are a local adaption of the traditional Chinese system, which was adopted at a very early date. They were imposed and adjusted at various times by local and imperial statutes. The details of the system have varied over time and location in Japan's history.
Japan signed the Treaty of the Metre in 1885, with its terms taking effect in 1886. It received its prototype metre and kilogram from the International Bureau of Weights and Measures in 1890. The next year, a weights and measurements law codified the Japanese system, taking its fundamental units to be the shaku and kan and deriving the others from them. The law codified the values of the traditional and metric units in terms of one another, but retained the traditional units as the formal standard and metric values as secondary. | Japanese units of measurement | Wikipedia | 422 | 2985420 | https://en.wikipedia.org/wiki/Japanese%20units%20of%20measurement | Physical sciences | Measurement systems | Basics and measurement |
In 1909, English units were also made legal within the Empire of Japan. Following World War I, the Ministry of Agriculture and Commerce established a Committee for Weights and Measures and Industrial Standards, part of whose remit was to investigate which of Japan's three legal systems should be adopted. Upon its advice, the Imperial Diet established the metric system as Japan's legal standard, effective 1 July 1924, with use of the other systems permitted as a transitional measure. The government and "leading industries" were to convert within the next decade, with others following in the decade after that. Public education—at the time compulsory through primary school—began to teach the metric system. Governmental agencies and the Japanese Weights and Measures Association undertook a gradual course of education and conversion but opposition became vehemently outspoken in the early 1930s. Nationalists decried the "foreign" system as harmful to Japanese pride, language, and culture, as well as restrictive to international trade. In 1933, the government pushed the deadline for the conversion of the first group of industries to 1939; the rest of the country was given until 1954. Emboldened, the nationalists succeeded in having an Investigating Committee for Weights and Measures Systems established. In 1938, it advised that the government should continue to employ the "Shaku–Kan" system alongside the metric one. The next year, the imperial ordinance concerning the transition to the metric system was formally revised, indefinitely exempting real estate and historical objects and treasures from any need for metric conversion. The deadline for compulsory conversion in all other fields was moved back to 31 December 1958.
Following its defeat in World War II, Japan was occupied by America and saw an expanded use of US customary units. Gasoline was sold by the gallon and cloth by the yard. The Diet revisited the nation's measurements and, with the occupation's approval, promulgated a Measurements Law in June 1951 that reaffirmed its intention to continue Japan's metrication, effective on the first day of 1959. An unofficial and ad hoc Metric System Promotion Committee was established by interested scholars, public servants, and businessmen in August 1955, undertaking a public awareness campaign and seeking to accomplish as much of the conversion ahead of schedule as possible. Its first success was the conversion of candy sales in Tokyo department stores from the momme to the gram in September 1956; others followed, with NHK taking the lead in media use. | Japanese units of measurement | Wikipedia | 480 | 2985420 | https://en.wikipedia.org/wiki/Japanese%20units%20of%20measurement | Physical sciences | Measurement systems | Basics and measurement |
With the majority of the public now exposed to it since childhood, the metric system became the sole legal measurement system in most fields of Japanese life on 1 January 1959. Redrafting of laws to use metric equivalents had already been accomplished, but conversion of the land registries required until 31 March 1966 to complete. Industry transitioned gradually at its own expense, with compliance sometimes being nominal, as in the case of screws becoming " screws". Since the original fines for noncompliance were around $140 and governmental agencies mostly preferred to wait for voluntary conversion, metric use by December 1959 was estimated at only 85%. Since research showed that individual Japanese did not intend to actually use the metric units when given other options, however, sale and verification of devices marked with non-metric units (such as rulers and tape measures noting shaku and sun) were criminalised after 1961.
Some use of the traditional units continues. Some Japanese describe their weight in terms of kan. Homes continue to be reckoned in terms of tsubo, even on the national census as late as 2005, although the practice was discontinued in 2010. English units continue to be employed in aviation, munitions, and various sports, including golf and baseball.
Length
The base unit of Japanese length is the shaku based upon the Chinese chi, with other units derived from it and changing over time based on its dimensions. The chi was originally a span taken from the end of the thumb to the tip of an outstretched middle finger, but which gradually increased in length to about , just a few centimetres longer than the size of a foot.
As in China and Korea, Japan employed different shaku for different purposes. The "carpentry" shaku (, kanejaku) was used for construction. It was a little longer in the 19th century prior to its metric redefinition. The "cloth" or "whale" shaku (, kujirajaku), named for tailors' and fabric merchants' baleen rulers, was longer and used in measuring cloth. (A longer unit of about 25cloth shaku was the tan.) Traditional Japanese clothing was reckoned using the "traditional clothing" shaku (, gofukujaku), about longer than the carpentry shaku. The Shōsōin in Nara has ivory 1-shaku rulers, the . | Japanese units of measurement | Wikipedia | 478 | 2985420 | https://en.wikipedia.org/wiki/Japanese%20units%20of%20measurement | Physical sciences | Measurement systems | Basics and measurement |
The Japanese ri is now much longer than the Chinese or Korean li, comprising 36 chō, 2160 ken, or 12,960shaku. A still longer unit was formerly standard in Ise on Honshu and throughout the 9 provinces of Kyushu, which comprised 50 chō, 3000 ken, or 18,000shaku. The imperial nautical mile of 6080feet (1853.19m) was also formerly used by the Japanese in maritime contexts as a "marine ri". A fourth and shorter ri of about 600m is still evident in some beach names. The "99-Ri" beach at Kujukuri is about 60 km. The "7-Ri" beach at Shichiri is 4.2 km long.
The traditional units are still used for construction materials in Japan. For example, plywood is usually manufactured in (about ) sheets known in the trade as , or 3 × 6 shaku. Each sheet is about the size of one tatami mat. The thicknesses of the sheets, however, are usually measured in millimetres. The names of these units also live in the name of the bamboo flute , literally "shaku eight", which measures one shaku and eight sun, and the Japanese version of the Tom Thumb story, , literally "one sun boy", as well as in many Japanese proverbs.
Area
The base unit of Japanese area is the tsubo, equivalent to a square ken or 36 square shaku. It is twice the size of the jō, the area of the Nagoya tatami mat. Both units are used informally in discussing real estate floorspace. Due to historical connections, the tsubo is still used as the official base unit of area in Taiwan.
In agricultural contexts, the tsubo is known as the bu. The larger units remain in common use by Japanese farmers when discussing the sizes of fields.
Volume
The base unit of Japanese volume is the shō, although the gō now sees more use since it is reckoned as the appropriate size of a serving of rice or sake. Sake and shochu are both commonly sold in large 1800mL bottles known as , literally "one shō bottle". | Japanese units of measurement | Wikipedia | 438 | 2985420 | https://en.wikipedia.org/wiki/Japanese%20units%20of%20measurement | Physical sciences | Measurement systems | Basics and measurement |
The koku is historically important: since it was reckoned as the amount of rice necessary to feed a person for a single year, it was used to compute agricultural output and official salaries. The koku of rice was sometimes reckoned as 3000"sacks". By the 1940s the shipping koku was of the shipping ton of 40 or 42cuft (i.e., ); the koku of timber was about 10cuft (); and the koku of fish, like many modern bushels, was no longer reckoned by volume but computed by weight (40kan). The shakujime of timber was about 12cuft () and the taba about 108ft³ ( or ).
Mass
The base unit of Japanese mass is the kan, although the momme is more common. It is a recognised unit in the international pearl industry. In English-speaking countries, momme is typically abbreviated as mo.
The Japanese form of the Chinese tael was the ryō (). It was customarily reckoned as around 4 or 10 momme but, because of its importance as a fundamental unit of the silver and gold bullion used as currency in medieval Japan, it varied over time and location from those notional values.
Imperial units
Imperial units are sometimes used in Japan. Feet and inches are used for most non-sport bicycles, whose tyre sizes follow a British system; for sizes of magnetic tape and many pieces of computer hardware; for photograph sizes; and for the sizes of electronic displays for electronic devices. Photographic prints, however, are usually rounded to the nearest millimetre and screens are not described in terms of inches but "type" (, gata). For instance, a television whose screen has a 17-inch diagonal is described as a "17-type" () and one with a 32-inch widescreen screen is called a "32-vista-type" (). | Japanese units of measurement | Wikipedia | 393 | 2985420 | https://en.wikipedia.org/wiki/Japanese%20units%20of%20measurement | Physical sciences | Measurement systems | Basics and measurement |
Copper(II) acetate, also referred to as cupric acetate, is the chemical compound with the formula Cu(OAc)2 where AcO− is acetate (). The hydrated derivative, Cu2(OAc)4(H2O)2, which contains one molecule of water for each copper atom, is available commercially. Anhydrous copper(II) acetate is a dark green crystalline solid, whereas Cu2(OAc)4(H2O)2 is more bluish-green. Since ancient times, copper acetates of some form have been used as fungicides and green pigments. Today, copper acetates are used as reagents for the synthesis of various inorganic and organic compounds. Copper acetate, like all copper compounds, emits a blue-green glow in a flame.
Structure
Copper acetate hydrate adopts the paddle wheel structure seen also for related Rh(II) and Cr(II) tetraacetates. One oxygen atom on each acetate is bound to one copper atom at 1.97 Å (197 pm). Completing the coordination sphere are two water ligands, with Cu–O distances of 2.20 Å (220 pm). The two copper atoms are separated by only 2.62 Å (262 pm), which is close to the Cu–Cu separation in metallic copper. The two copper centers interact resulting in a diminishing of the magnetic moment such that at temperatures below 90 K, Cu2(OAc)4(H2O)2 is essentially diamagnetic. Cu2(OAc)4(H2O)2 was a critical step in the development of modern theories for antiferromagnetic exchange coupling, which ascribe its low-temperature diamagnetic behavior to cancellation of the two opposing spins on the adjacent copper atoms.
Synthesis
Copper(II) acetate is prepared industrially by heating copper(II) hydroxide or basic copper(II) carbonate with acetic acid. | Copper(II) acetate | Wikipedia | 418 | 2987828 | https://en.wikipedia.org/wiki/Copper%28II%29%20acetate | Physical sciences | Acetates | Chemistry |
Uses in chemical synthesis
Copper(II) acetate has found some use as an oxidizing agent in organic syntheses. In the Eglinton reaction Cu2(OAc)4 is used to couple terminal alkynes to give a 1,3-diyne:
Cu2(OAc)4 + 2 RC≡CH → 2 CuOAc + RC≡C−C≡CR + 2 HOAc
The reaction proceeds via the intermediacy of copper(I) acetylides, which are then oxidized by the copper(II) acetate, releasing the acetylide radical. A related reaction involving copper acetylides is the synthesis of ynamines, terminal alkynes with amine groups using Cu2(OAc)4. It has been used for hydroamination of acrylonitrile.
It is also an oxidising agent in Barfoed's test.
It reacts with arsenic trioxide to form copper acetoarsenite, a powerful insecticide and fungicide called Paris green.
Related compounds
Heating a mixture of anhydrous copper(II) acetate and copper metal affords copper(I) acetate:
Cu + Cu(OAc)2 → 2 CuOAc
Unlike the copper(II) derivative, copper(I) acetate is colourless and diamagnetic.
"Basic copper acetate" is prepared by neutralizing an aqueous solution of copper(II) acetate. The basic acetate is poorly soluble. This material is a component of verdigris, the blue-green substance that forms on copper during long exposures to atmosphere.
Other uses
A mixture of copper acetate and ammonium chloride is used to chemically color copper with a bronze patina.
Mineralogy
The mineral hoganite is a naturally occurring form of copper(II) acetate. A related mineral, also containing calcium, is paceite. Both are very rare. | Copper(II) acetate | Wikipedia | 399 | 2987828 | https://en.wikipedia.org/wiki/Copper%28II%29%20acetate | Physical sciences | Acetates | Chemistry |
Calcium acetate is a chemical compound which is a calcium salt of acetic acid. It has the formula Ca(C2H3O2)2. Its standard name is calcium acetate, while calcium ethanoate is the systematic name. An older name is acetate of lime. The anhydrous form is very hygroscopic; therefore the monohydrate (Ca(CH3COO)2•H2O) is the common form.
Production
Calcium acetate can be prepared by soaking calcium carbonate (found in eggshells, or in common carbonate rocks such as limestone or marble) or hydrated lime in vinegar:
CaCO3(s) + 2CH3COOH(aq) → Ca(CH3COO)2(aq) + H2O(l) + CO2(g)
Ca(OH)2(s) + 2CH3COOH(aq) → Ca(CH3COO)2(aq) + 2H2O(l)
Since both reagents would have been available pre-historically, the chemical would have been observable as crystals then.
Uses
In kidney disease, blood levels of phosphate may rise (called hyperphosphatemia) leading to bone problems. Calcium acetate binds phosphate in the diet to lower blood phosphate levels.
Calcium acetate is used as a food additive, as a stabilizer, buffer and sequestrant, mainly in candy products under the number E263.
Tofu is traditionally obtained by coagulating soy milk with calcium sulfate. Calcium acetate has been found to be a better alternative; being soluble, it requires less skill and a smaller amount.
Because it is inexpensive, calcium acetate was once a common starting material for the synthesis of acetone before the development of the cumene process:
Ca(CH3COO)2 → CaCO3(s) + (CH3)2CO
A saturated solution of calcium acetate in alcohol forms a semisolid, flammable gel that is much like "canned heat" products such as Sterno. Chemistry teachers often prepare "California Snowballs", a mixture of calcium acetate solution and ethanol. The resulting gel is whitish in color, resembling a snowball and can be lit on fire; it will burn for around 20 minutes. | Calcium acetate | Wikipedia | 479 | 2988583 | https://en.wikipedia.org/wiki/Calcium%20acetate | Physical sciences | Acetates | Chemistry |
Natural occurrence
Pure calcium acetate is yet unknown among minerals. calcium acetate chloride is listed as a known mineral, but its genesis is anthropogenic (human-generated, as opposed to naturally occurring). | Calcium acetate | Wikipedia | 43 | 2988583 | https://en.wikipedia.org/wiki/Calcium%20acetate | Physical sciences | Acetates | Chemistry |
Chromium(II) acetate hydrate, also known as chromous acetate, is the coordination compound with the formula Cr2(CH3CO2)4(H2O)2. This formula is commonly abbreviated Cr2(OAc)4(H2O)2. This red-coloured compound features a quadruple bond. The preparation of chromous acetate once was a standard test of the synthetic skills of students due to its sensitivity to air and the dramatic colour changes that accompany its oxidation. It exists as the dihydrate and the anhydrous forms.
Cr2(OAc)4(H2O)2 is a reddish diamagnetic powder, although diamond-shaped tabular crystals can be grown. Consistent with the fact that it is nonionic, Cr2(OAc)4(H2O)2 exhibits poor solubility in water and methanol.
Structure
The Cr2(OAc)4(H2O)2 molecule contains two atoms of chromium, two ligated molecules of water, and four acetate bridging ligands. The coordination environment around each chromium atom consists of four oxygen atoms (one from each acetate ligand) in a square, one water molecule (in an axial position), and the other chromium atom (opposite the water molecule), giving each chromium centre an octahedral geometry. The chromium atoms are joined by a quadruple bond, and the molecule has D4h symmetry (ignoring the position of the hydrogen atoms). The same basic structure is adopted by Rh2(OAc)4(H2O)2 and Cu2(OAc)4(H2O)2, although these species do not have such short M–M contacts. | Chromium(II) acetate | Wikipedia | 379 | 2988743 | https://en.wikipedia.org/wiki/Chromium%28II%29%20acetate | Physical sciences | Acetates | Chemistry |
The quadruple bond between the two chromium atoms arises from the overlap of four d-orbitals on each metal with the same orbitals on the other metal: the dz2 orbitals overlap to give a sigma bonding component, the dxz and dyz orbitals overlap to give two pi bonding components, and the dxy orbitals give a delta bond. This quadruple bond is also confirmed by the low magnetic moment and short intermolecular distance between the two atoms of 236.2 ± 0.1 pm. The Cr–Cr distances are even shorter, 184 pm being the record, when the axial ligand is absent or the carboxylate is replaced with isoelectronic nitrogenous ligands.
History
Eugène-Melchior Péligot first reported a chromium(II) acetate in 1844. His material was apparently the dimeric Cr2(OAc)4(H2O)2. The unusual structure, as well as that of copper(II) acetate, was uncovered in 1951.
Preparation
The preparation usually begins with reduction of an aqueous solution of a Cr(III) compound using zinc. The resulting blue solution is treated with sodium acetate, which results in the rapid precipitation of chromous acetate as a bright red powder.
2 Cr3+ + Zn → 2 Cr2+ + Zn2+
2 Cr2+ + 4 OAc− + 2 H2O → Cr2(OAc)4(H2O)2
The synthesis of Cr2(OAc)4(H2O)2 has been traditionally used to test the synthetic skills and patience of inorganic laboratory students in universities because the accidental introduction of a small amount of air into the apparatus is readily indicated by the discoloration of the otherwise bright red product. The anhydrous form of chromium(II) acetate, and also related chromium(II) carboxylates, can be prepared from chromocene:
4 RCO2H + 2 Cr(C5H5)2 → Cr2(O2CR)4 + 4 C5H6
This method provides anhydrous derivatives in a straightforward manner. | Chromium(II) acetate | Wikipedia | 457 | 2988743 | https://en.wikipedia.org/wiki/Chromium%28II%29%20acetate | Physical sciences | Acetates | Chemistry |
Because it is so easily prepared, Cr2(OAc)4(H2O)2 is a starting material for other chromium(II) compounds. Also, many analogues have been prepared using other carboxylic acids in place of acetate and using different bases in place of the water.
Applications
Chromium(II) acetate has few practical applications. It has been used to dehalogenate organic compounds such as α-bromoketones and chlorohydrins. The reactions appear to proceed via 1e− steps, and rearrangement products are sometimes observed.
Because the compound is a good reducing agent, it will reduce the O2 found in air and can be used as an oxygen scrubber. | Chromium(II) acetate | Wikipedia | 153 | 2988743 | https://en.wikipedia.org/wiki/Chromium%28II%29%20acetate | Physical sciences | Acetates | Chemistry |
Ferret-badgers are the six species of the genus Melogale, which is the only genus of the monotypic mustelid subfamily Helictidinae.
Bornean ferret-badger (Melogale everetti)
Chinese ferret-badger (Melogale moschata)
Formosan ferret-badger (Melogale subaurantiaca)
Javan ferret-badger (Melogale orientalis)
Burmese ferret-badger (Melogale personata)
Vietnam ferret-badger (Melogale cucphuongensis)
Human impact
The ferret-badger's impact on humans is through the spread of rabies. This has been documented in Taiwan and China but lack of prior documentation and research on ferret-badgers has proven a roadblock. | Ferret-badger | Wikipedia | 165 | 6974397 | https://en.wikipedia.org/wiki/Ferret-badger | Biology and health sciences | Mustelidae | Animals |
In continuum mechanics, shearing refers to the occurrence of a shear strain, which is a deformation of a material substance in which parallel internal surfaces slide past one another. It is induced by a shear stress in the material. Shear strain is distinguished from volumetric strain. The change in a material's volume in response to stress and change of angle is called the angle of shear.
Overview
Often, the verb shearing refers more specifically to a mechanical process that causes a plastic shear strain in a material, rather than causing a merely elastic one. A plastic shear strain is a continuous (non-fracturing) deformation that is irreversible, such that the material does not recover its original shape. It occurs when the material is yielding. The process of shearing a material may induce a volumetric strain along with the shear strain. In soil mechanics, the volumetric strain associated with shearing is known as Reynolds' dilation if it increases the volume, or compaction if it decreases the volume.
The shear center (also known as the torsional axis) is an imaginary point on a section, where a shear force can be applied without inducing any torsion. In general, the shear center is not the centroid. For cross-sectional areas having one axis of symmetry, the shear center is located on the axis of symmetry. For those having two axes of symmetry, the shear center lies on the centroid of the cross-section.
In some materials such as metals, plastics, or granular materials like sand or soils, the shearing motion rapidly localizes into a narrow band, known as a shear band. In that case, all the sliding occurs within the band while the blocks of material on either side of the band simply slide past one another without internal deformation. A special case of shear localization occurs in brittle materials when they fracture along a narrow band. Then, all subsequent shearing occurs within the fracture. Plate tectonics, where the plates of the Earth's crust slide along fracture zones, is an example of this.
Shearing in soil mechanics is measured with a triaxial shear test or a direct shear test. | Shearing (physics) | Wikipedia | 433 | 7139621 | https://en.wikipedia.org/wiki/Shearing%20%28physics%29 | Physical sciences | Solid mechanics | Physics |
The dwarf crocodile (Osteolaemus tetraspis), also known as the African dwarf crocodile, broad-snouted crocodile (a name more often used for the Asian mugger crocodile) or bony crocodile, is an African crocodile that is also the smallest extant (living) species of crocodile.
Description
Dwarf crocodiles attain a medium adult length of , though the maximum recorded length for this species is . Adult specimens typically weigh between , with the largest females weighing up to and the largest males weighing . This makes it the smallest living crocodile species, although the Cuvier's dwarf caiman (Paleosuchus palpebrosus), a member of the family Alligatoridae, is smaller at up to about . If the Congo dwarf crocodile (O. osborni) is recognized as a valid species, it would be both the smallest crocodile and the smallest crocodilian since it does not surpass . Adults are all dark above and on their sides, while the underside is yellowish with black patches.
Some individuals living in the caves of Abanda, Gabon, displayed orange patches, apparently due to alkaline bat guano that erodes the skin of the crocodile. Juveniles have a lighter brown banding on body and tails and yellow patterns on the head.
As a result of its small size and heightened vulnerability to predation, this species of crocodile has a heavily armoured neck, back, and tail and also has osteoderms on its belly and underside of neck.
Osteolaemus has a blunt short snout, as long as it is wide, similar to that of a Cuvier's dwarf caiman, probably a result of occupying a similar ecological niche. The dentition consists of four premaxillary teeth, 12 to 13 on the maxilla, and 14 to 15 on the dentary bone.
O. t. tetraspis has lighter colours, a more pointed, upturned snout, and more body armour than O. t. osborni.
Distribution and habitat
Dwarf crocodiles range across tropical regions of Sub-Saharan West Africa and Central Africa. Such a distribution greatly overlaps with that of the slender-snouted crocodile, encompassing countries as far west as Senegal, reaching Uganda in the east, and ranging as southerly as Angola. The last confirmed record from Uganda was in the 1940s, but whether the species, which is easily overlooked, still survives there is unclear (it was always marginal in this country, only occurring in the far southwest). | Dwarf crocodile | Wikipedia | 504 | 7139731 | https://en.wikipedia.org/wiki/Dwarf%20crocodile | Biology and health sciences | Crocodilia | Animals |
Dwarf crocodiles live from lowlands to mid-altitude in streams, small rivers, swamps, pools and mangrove, but generally avoid main sections of large rivers. Most of their range is within forested regions, but it may extend into more open regions where the streams or river are well-shaded. They are also found in seasonally-flooded forest. Unlike most crocodiles, dwarf crocodiles only rarely bask in the sun. During the night they may move some distance from water on land. Reports exist of dwarf crocodiles in isolated pools in the savannah. Dwarf crocodiles living long-term in caves are known from western Gabon, which stand out as an isolated genetic group.
Biology and behaviour
The dwarf crocodile is a timid and mainly nocturnal reptile that spends the day hidden in pools or burrows, although it occasionally may be active during the day. Foraging is mainly done in or near the water, although it is considered to be one of the most terrestrial species of crocodilian and may expand the feeding pattern to land in extensive forays, especially after rains.
Dwarf crocodiles are generalist predators and have been recorded feeding on a wide range of small animals such as fish, crabs, frogs, gastropods, insects, lizards, water birds, bats and shrews.
In a study in the Democratic Republic of the Congo the primary food item was fish, and in a study in Nigeria the primary food items were gastropods and crabs. In the Congo there is a level of seasonality in its diet, changing from fish in the wet season to crustaceans in the dry season, when fish are less available. Plant material has also been found in the stomach of dwarf crocodiles, but it is suspected that this is ingested by accident. They can survive for relatively long periods without food. During the dry season, dwarf crocodiles often retreat to deep holes.True to its solitary, nocturnal nature, a dwarf crocodile digs out a burrow in which to hide and rest during the day, which can sometimes have a submerged entrance. An individual lacking the right conditions to do so usually lives between tree roots that hang over the ponds where it lives. | Dwarf crocodile | Wikipedia | 434 | 7139731 | https://en.wikipedia.org/wiki/Dwarf%20crocodile | Biology and health sciences | Crocodilia | Animals |
Reproduction
Interacting closely only in breeding season, female dwarf crocodiles build their nest mounds at the beginning of the wet season, which spans May and June. The nest, situated near the water, is a mound of wet, decaying vegetation that incubates the eggs due to the heat generated by the decomposition of the plant material. A small number of eggs is laid, usually about 10, though in extreme cases up to 20, and they incubate in 85 to 105 days. Hatchlings measure 28 cm when emerging from the eggs. The female guards the nest during the incubation period, and after the eggs hatch, she watches over the young for an unknown period of time, as young can be eaten by a great range of predators (birds, fish, mammals and reptiles, including other crocodiles).
Taxonomy and etymology
The second species has had a somewhat convoluted taxonomical history. It was first described as Osteoblepharon osborni by Schmidt in 1919, based on a few specimens from the Upper Congo River Basin in what is now the Democratic Republic of Congo. However, Inger in a 1948 paper found the specimens wanting of characteristics that would justify a generic separation from Osteolaemus and referred the specimens to Osteolaemus osborni. In 1961, it was reduced to subspecies rank.
A study of morphology published in 2007, and studies of DNA in 2009, 2013 and 2015 indicate that three distinctly different populations of Osteolaemus may merit full species recognition. These are O. tetraspis (Central Africa, except the Congo River Basin), O. osborni (Congo River Basin), and a third possibly unnamed species (West Africa). Uncertainty exists for the population in Nigeria (between O. tetraspis and the possibly unnamed West African species) as it has not been studied. A fourth clade was found in a study of captives in 2013, but where members of this clade live in the wild is unclear. In some regions the species may come into contact. For example, Cameroon is home to both O. tetraspis and O. osborni.
Etymology
The generic name, Osteolaemus, means "bony throat", and is derived from the Ancient Greek (bone) and (throat). The genus was named as such due to the osteoderms found among the scales in the neck and belly. | Dwarf crocodile | Wikipedia | 487 | 7139731 | https://en.wikipedia.org/wiki/Dwarf%20crocodile | Biology and health sciences | Crocodilia | Animals |
The specific epithet, tetraspis, means "four shields", and derives from the Ancient Greek (four) and (shield), as the back of the neck has four large, shield-like scales.
Phylogeny
A 2018 tip dating study by Lee & Yates simultaneously using morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data established the inter-relationships within Crocodylidae. In 2021, Hekkala et al. were able to use paleogenomics, extracting DNA from the extinct Voay, to better establish the relationships within Crocodylidae, including the subfamilies Crocodylinae and Osteolaeminae.
The below cladogram shows the results of the latest study:
Conservation
The dwarf crocodile is considered vulnerable by the IUCN, and it is listed on Appendix I of CITES. It is a little-known species, so unlike their more studied relatives, conservationists are often not as aware of how their populations are faring under the growing human pressure over the ecosystems where they abide. Survey data, when available, show some degree of decline, either by hunting for bushmeat or habitat loss due to deforestation. However, it is a widely spread, and presumably numerous overall. In some regions the populations remain healthy, but in others (such as Gambia and Liberia) it has seriously declined and may risk extirpation. Dwarf crocodiles occur in several protected reserves.
Though some skins are used in local manufacturing of leather products, they are of poor quality, so little interest is shown in captive breeding or a sustainable use program. In contrast, they are sometimes hunted for food and part of the bushmeat trade.
Dwarf crocodiles are widely kept and bred in zoos. Based on a study of individuals kept in AZA zoos, captives in North America are primarily O. tetrapis and the possibly unnamed West African species, but there are also some hybrids. Another study of individuals kept at EAZA zoos revealed a similar picture for Europe, but also that there were a few individuals of the fourth clade (native range in the wild unknown) and a single O. osborni.
Gallery | Dwarf crocodile | Wikipedia | 445 | 7139731 | https://en.wikipedia.org/wiki/Dwarf%20crocodile | Biology and health sciences | Crocodilia | Animals |
Soil steam sterilization (soil steaming) is a farming technique that sterilizes soil with steam in open fields or greenhouses. Pests of plant cultures such as weeds, bacteria, fungi and viruses are killed through induced hot steam which causes vital cellular proteins to unfold. Biologically, the method is considered a partial disinfection. Important heat-resistant, spore-forming bacteria can survive and revitalize the soil after cooling down. Soil fatigue can be cured through the release of nutritive substances blocked within the soil. Steaming leads to a better starting position, quicker growth and strengthened resistance against plant disease and pests. Today, the application of hot steam is considered the best and most effective way to disinfect sick soil, potting soil and compost.
It is being used as an alternative to bromomethane, whose production and use was curtailed by the Montreal Protocol. "Steam effectively kills pathogens by heating the soil to levels that cause protein coagulation or enzyme inactivation."
Benefits of soil steaming
Soil sterilization provides secure and quick relief of soils from substances and organisms harmful to plants such as:
Bacteria
Viruses
Fungi
Nematodes
Other pests
Further positive effects are:
All weeds and weed seeds are killed
Significant increase of crop yields
Relief from soil fatigue through activation of chemical – biological reactions
Blocked nutritive substances in the soil are tapped and made available for plants
Alternative to methyl bromide and other critical chemicals in agriculture
Steaming with superheated steam
Through modern steaming methods with superheated steam at 180–200 °C, an optimal soil disinfection can be achieved. Soil only absorbs a small amount of humidity. Micro organisms become active once the soil has cooled down. This creates an optimal environment for instant tillage with seedlings and seeds.
Additionally the method of integrated steaming can promote a target-oriented resettlement of steamed soil with beneficial organisms. In the process, the soil is first freed from all organisms and then revitalized and microbiologically buffered through the injection of a soil activator based on compost which contains a natural mixture of favorable microorganisms (e.g. Bacillus subtilis, etc.).
Different types of such steam application are also available in practice, including substrate steaming, surface steaming, and deep soil steaming. | Soil steam sterilization | Wikipedia | 474 | 15946878 | https://en.wikipedia.org/wiki/Soil%20steam%20sterilization | Technology | Pest and disease control | null |
Surface steaming
Several methods for surface steaming are in use amongst which are: area sheet steaming, the steaming hood, the steaming harrow, the steaming plough and vacuum steaming with drainage pipes or mobile pipe systems.
In order to pick the most suitable steaming method, certain factors have to be considered such as soil structure, plant culture and area performance. At present, more advanced methods are being developed, such as sandwich steaming or partially integrated sandwich steaming in order to minimize energy consumption and associated costs as much as possible.
Deep soil steaming
Deep soil steaming is a concept adopted by the Norwegian company Soil Steam international AS. They have developed a technology that gets the steam down to 30 cm deep in the soil. This is done in a continuous process and their last prototype managed to treat 1 hectare in 20 hours. When steaming the soil this deep, they get deep enough to prevent fall plowing from bringing up new seeds, fungi or nematodes. This means that the soil stays free from weeds, seeds, fungi and nematodes for many years after one deep soil steam operation.
Sheet steaming
Surface steaming with special sheets (sheet steaming) is a method which has been established for decades in order to steam large areas reaching from 15 to 400 m2 in one step. If properly applied, sheet steaming is simple and highly economic. The usage of heat resistant, non-decomposing insulation fleece saves up to 50% energy, reduces the steaming time significantly and improves penetration. Single working step areas up to 400 m2 can be steamed in 4–5 hours down to 25–30 cm depth / 90 °C.
The usage of heat resistant and non-decomposing synthetic insulation fleece, 5 mm thick, 500 gr / m2, can reduce steaming time by about 30%. Through a steam injector or a perforated pipe, steam is injected underneath the sheet after it has been laid out and weighted with sand sacks.
The area performance in one working step depends on the capacity of the steam generator (e.g. steam boiler):
The steaming time depends on soil structure as well as outside temperature and amounts to 1–1.5 hours per 10 cm steaming depth. Hereby the soil reaches a temperature of about 85 °C. Milling for soil loosening is not recommended since soil structure may become too fine which reduces its penetrability for steam. The usage of spading machines is ideal for soil loosening. The best results can be achieved if the soil is cloddy at greater depth and granulated at lesser depth. | Soil steam sterilization | Wikipedia | 507 | 15946878 | https://en.wikipedia.org/wiki/Soil%20steam%20sterilization | Technology | Pest and disease control | null |
In practice, working with at least two sheets simultaneously has proven to be highly effective. While one sheet is used for steaming the other one is prepared for steam injection, therefore unnecessary steaming recesses are avoided.
Depth steaming with vacuum
Steaming with vacuum which is induced through a mobile or fixed installed pipe system in the depth of the area to be steamed, is the method that reaches the best penetration. Despite high capital cost, the fixed installation of drainage systems is reasonable for intensively used areas since steaming depths of up to 80 cm can be achieved.
In contrast to fixed installed drainage systems, pipes in mobile suction systems are on the surface. A central suction pipeline consisting of zinc-coated, fast-coupling pipes are connected in a regular spacing of 1.50 m and the ends of the hoses are pushed into the soil to the desired depth with a special tool.
The steaming area is covered with a special steaming sheet and weighted all around as with sheet steaming. The steam is injected underneath the sheet through an injector and protection tunnel. While with short areas up to 30 m length steam is frontally injected, with longer areas steam is induced in the middle of the sheet using a T-connection branching out to both sides.
As soon as the sheet is inflated to approximately 1 m by the steam pressure, the suction turbine is switched on. First, the air in the soil is removed via the suction hoses. A partial vacuum is formed and the steam is pulled downward.
During the final phase, when the required steaming depth has been reached, the ventilator runs non-stop and surplus steam is blown out. To ensure that this surplus steam is not lost, it is fed back under the sheet.
As with all other steaming systems, a post-steaming period of approximately 20–30 minutes is required. Steaming time is approximately 1 hour per 10 cm steaming depth. The steam requirement is approximately 7–8 kg/m2.
The most important requirement, as with all steaming systems, is that the soil is well loosened before steaming, to ensure optimal penetration. | Soil steam sterilization | Wikipedia | 418 | 15946878 | https://en.wikipedia.org/wiki/Soil%20steam%20sterilization | Technology | Pest and disease control | null |
Negative pressure technique
Negative pressure technique generates appropriate soil temperature at a 60 cm depth and complete control of nematodes, fungi and weeds is achieved. In this technique, the steam is introduced under the steaming sheath and forced to enter the soil profile by a negative pressure. The negative pressure is created by a fan that sucks the air out of the soil through buried perforated polypropylene pipes. This system requires a permanent installation of perforated pipes into the soil, at a depth of at least 60 cm to be protected from plough.
Steaming with hoods
A steaming hood is a mobile device consisting of corrosion-resistant materials such as aluminum, which is put down onto the area to be steamed. In contrast to sheet steaming, cost-intensive working steps such as laying out and weighting the sheets don't occur, however the area steamed per working step is smaller in accordance to the size of the hood.
Outdoors, a hood is positioned either manually or via tractor with a special pre-stressed 4 point suspension arm. Steaming time amounts to 30 min for a penetration down to 25 cm depth. Hereby a temperature of 90 °C can be reached. In large stable glasshouses, the hoods are attached to tracks. They are lifted and moved by pneumatic cylinders. Small and medium-sized hoods up to 12 m2 are lifted manually using a tipping lever or moved electrically with special winches.
Combined surface and depth injection of steam (Sandwich Steaming)
Sandwich steaming, which was developed in a project among DEIAFA, University of Turin (Italy, www.deiafa.unito.it) and Ferrari Costruzioni Meccaniche (see image), represents a combination of depth and surface steaming, offers an efficient method to induce hot steam into the soil. The steam is simultaneously pushed into the soil from the surface and from the depth. For this purpose, the area, which must be equipped with a deep steaming injection system, is covered with a steaming hood. The steam enters the soil from the top and the bottom at the same time. Sheets are not suitable, since a high pressure up to 30 mm water column arises underneath the cover. | Soil steam sterilization | Wikipedia | 438 | 15946878 | https://en.wikipedia.org/wiki/Soil%20steam%20sterilization | Technology | Pest and disease control | null |
Sandwich steaming offers several advantages. On the one hand, application of energy can be increased to up to 120 kg steam per m2/h. In comparison to other steaming methods up to 30% energy savings can be achieved and the usage of fuel (e.g. heating oil) accordingly decreases. The increased application of energy leads to a quick heating of the soil which reduces the loss of heat. On the other hand, only half of the regular steaming time is needed.
Comparison of sandwich steaming with other steam injection methods relating to steam output and energy demand(*):
(*) in soil max 30% moisture
Clearly, Sandwich steaming reaches the highest steam output at the lowest energy demand.
Partially integrated sandwich steaming
The partial integrated sandwich steaming is an advanced combined method for steaming merely the areas which shall be planted and purposely leaving out those areas which shall not be used. In order to avoid risk of re-infection of steamed areas with pest from unsteamed areas, beneficial organisms can directly be injected into the hygenized soil via a soil activator (e.g. special compost). The partial sandwich steaming unlocks further potential savings in the steaming process.
Container / Stack steaming
Stack steaming is used when thermically treating compost and substrates such as turf. Depending on the amount, the material to be steamed is piled up to 70 cm height in steaming boxes or in small dump trailers. Steam is evenly injected via manifolds. For huge amounts, steaming containers and soil boxes are used which are equipped with suction systems to improve steaming results. Midget amounts can be steamed in special small steaming devices.
The amount of soil steamed should be tuned in a way that steaming time amounts to at most 1.5 h in order to avoid large quantities of condensed water in the bottom layers of the soil.
In light substrates, such as turf, the performance per hour is significantly higher. | Soil steam sterilization | Wikipedia | 383 | 15946878 | https://en.wikipedia.org/wiki/Soil%20steam%20sterilization | Technology | Pest and disease control | null |
History
Modern soil steam sterilization was first discovered in 1888 (by Frank in Germany) and was first commercially used in the United States (by Rudd) in 1893 (Baker 1962). Since then, a wide variety of steam machines have been built to disinfest both commercial greenhouse and nursery field soils (Grossman and Liebman 1995). In the 1950s, for example, steam sterilization technologies expanded from disinfestation of potting soil and greenhouse mixes to commercial production of steam rakes and tractor-drawn steam blades for fumigating small acres of cut flowers and other high-value field crops (Langedijk 1959). Today, even more effective steam technologies are being developed.
Application of hot steam
In horticulture as well as nurseries for sterilization of substrates and top soil
In agriculture for sterilization and treatment of food waste for pig fattening and heating of molasses
In mushroom cultivation for pasteurization of growing rooms, sterilization of top soil and combined application as heating
In wineries as combination boiler for sterilization and cleaning of storage tanks, tempering of mash and for warm water generation. | Soil steam sterilization | Wikipedia | 236 | 15946878 | https://en.wikipedia.org/wiki/Soil%20steam%20sterilization | Technology | Pest and disease control | null |
Parthenogenesis (; from the Greek + ) is a natural form of asexual reproduction in which the embryo develops directly from an egg without need for fertilization. In animals, parthenogenesis means development of an embryo from an unfertilized egg cell. In plants, parthenogenesis is a component process of apomixis. In algae, parthenogenesis can mean the development of an embryo from either an individual sperm or an individual egg.
Parthenogenesis occurs naturally in some plants, algae, invertebrate animal species (including nematodes, some tardigrades, water fleas, some scorpions, aphids, some mites, some bees, some Phasmatodea, and parasitic wasps), and a few vertebrates, such as some fish, amphibians, and reptiles. This type of reproduction has been induced artificially in animal species that naturally reproduce through sex, including fish, amphibians, and mice.
Normal egg cells form in the process of meiosis and are haploid, with half as many chromosomes as their mother's body cells. Haploid individuals, however, are usually non-viable, and parthenogenetic offspring usually have the diploid chromosome number. Depending on the mechanism involved in restoring the diploid number of chromosomes, parthenogenetic offspring may have anywhere between all and half of the mother's alleles. In some types of parthenogenesis the offspring having all of the mother's genetic material are called full clones and those having only half are called half clones. Full clones are usually formed without meiosis. If meiosis occurs, the offspring get only a fraction of the mother's alleles since crossing over of DNA takes place during meiosis, creating variation.
Parthenogenetic offspring in species that use either the XY or the X0 sex-determination system have two X chromosomes and are female. In species that use the ZW sex-determination system, they have either two Z chromosomes (male) or two W chromosomes (mostly non-viable but rarely a female), or they could have one Z and one W chromosome (female).
Life history types | Parthenogenesis | Wikipedia | 452 | 9276466 | https://en.wikipedia.org/wiki/Parthenogenesis | Biology and health sciences | Biological reproduction | Biology |
Parthenogenesis is a form of asexual reproduction in which the embryo develops directly from an egg without need for fertilization. It occurs naturally in some plants, algae, invertebrate animal species (including nematodes, some tardigrades, water fleas, some scorpions, aphids, some mites, some bees, some Phasmatodea, and parasitic wasps), and a few vertebrates, such as some fish, amphibians, reptiles, and birds. This type of reproduction has been induced artificially in a number of animal species that naturally reproduce through sex, including fish, amphibians, and mice.
Some species reproduce exclusively by parthenogenesis (such as the bdelloid rotifers), while others can switch between sexual reproduction and parthenogenesis. This is called facultative parthenogenesis (other terms are cyclical parthenogenesis, heterogamy or heterogony). The switch between sexuality and parthenogenesis in such species may be triggered by the season (aphid, some gall wasps), or by a lack of males or by conditions that favour rapid population growth (rotifers and cladocerans like Daphnia). In these species asexual reproduction occurs either in summer (aphids) or as long as conditions are favourable. This is because in asexual reproduction a successful genotype can spread quickly without being modified by sex or wasting resources on male offspring who will not give birth. Some species can produce both sexually and through parthenogenesis, and offspring in the same clutch of a species of tropical lizard can be a mix of sexually produced offspring and parthenogenically produced offspring. In California condors, facultative parthenogenesis can occur even when a male is present and available for a female to breed with. In times of stress, offspring produced by sexual reproduction may be fitter as they have new, possibly beneficial gene combinations. In addition, sexual reproduction provides the benefit of meiotic recombination between non-sister chromosomes, a process associated with repair of DNA double-strand breaks and other DNA damages that may be induced by stressful conditions. | Parthenogenesis | Wikipedia | 457 | 9276466 | https://en.wikipedia.org/wiki/Parthenogenesis | Biology and health sciences | Biological reproduction | Biology |
Many taxa with heterogony have within them species that have lost the sexual phase and are now completely asexual. Many other cases of obligate parthenogenesis (or gynogenesis) are found among polyploids and hybrids where the chromosomes cannot pair for meiosis.
The production of female offspring by parthenogenesis is referred to as thelytoky (e.g., aphids) while the production of males by parthenogenesis is referred to as arrhenotoky (e.g., bees). When unfertilized eggs develop into both males and females, the phenomenon is called deuterotoky.
Types and mechanisms
Parthenogenesis can occur without meiosis through mitotic oogenesis. This is called apomictic parthenogenesis. Mature egg cells are produced by mitotic divisions, and these cells directly develop into embryos. In flowering plants, cells of the gametophyte can undergo this process. The offspring produced by apomictic parthenogenesis are full clones of their mother, as in aphids.
Parthenogenesis involving meiosis is more complicated. In some cases, the offspring are haploid (e.g., male ants). In other cases, collectively called automictic parthenogenesis, the ploidy is restored to diploidy by various means. This is because haploid individuals are not viable in most species. In automictic parthenogenesis, the offspring differ from one another and from their mother. They are called half clones of their mother.
Automixis
Automixis includes several reproductive mechanisms, some of which are parthenogenetic.
Diploidy can be restored by the doubling of the chromosomes without cell division before meiosis begins or after meiosis is completed. This is an endomitotic cycle. Diploidy can also be restored by fusion of the first two blastomeres, or by fusion of the meiotic products. The chromosomes may not separate at one of the two anaphases (restitutional meiosis)l; or the nuclei produced may fuse; or one of the polar bodies may fuse with the egg cell at some stage during its maturation. | Parthenogenesis | Wikipedia | 462 | 9276466 | https://en.wikipedia.org/wiki/Parthenogenesis | Biology and health sciences | Biological reproduction | Biology |
Some authors consider all forms of automixis sexual as they involve recombination. Many others classify the endomitotic variants as asexual and consider the resulting embryos parthenogenetic. Among these authors, the threshold for classifying automixis as a sexual process depends on when the products of anaphase I or of anaphase II are joined. The criterion for sexuality varies from all cases of restitutional meiosis, to those where the nuclei fuse or to only those where gametes are mature at the time of fusion. Those cases of automixis that are classified as sexual reproduction are compared to self-fertilization in their mechanism and consequences.
The genetic composition of the offspring depends on what type of automixis takes place. When endomitosis occurs before meiosis or when central fusion occurs (restitutional meiosis of anaphase I or the fusion of its products), the offspring get all to more than half of the mother's genetic material and heterozygosity is mostly preserved (if the mother has two alleles for a locus, it is likely that the offspring will get both). This is because in anaphase I the homologous chromosomes are separated. Heterozygosity is not completely preserved when crossing over occurs in central fusion. In the case of pre-meiotic doubling, recombination, if it happens, occurs between identical sister chromatids.
If terminal fusion (restitutional meiosis of anaphase II or the fusion of its products) occurs, a little over half the mother's genetic material is present in the offspring and the offspring are mostly homozygous. This is because at anaphase II the sister chromatids are separated and whatever heterozygosity is present is due to crossing over. In the case of endomitosis after meiosis, the offspring is completely homozygous and has only half the mother's genetic material. This can result in parthenogenetic offspring being unique from each other and from their mother.
Sex of the offspring
In apomictic parthenogenesis, the offspring are clones of the mother and hence (except for aphids) are usually female. In the case of aphids, parthenogenetically produced males and females are clones of their mother except that the males lack one of the X chromosomes (XO). | Parthenogenesis | Wikipedia | 501 | 9276466 | https://en.wikipedia.org/wiki/Parthenogenesis | Biology and health sciences | Biological reproduction | Biology |
When meiosis is involved, the sex of the offspring depends on the type of sex determination system and the type of apomixis. In species that use the XY sex-determination system, parthenogenetic offspring have two X chromosomes and are female. In species that use the ZW sex-determination system the offspring genotype may be one of ZW (female), ZZ (male), or WW (non-viable in most species, but a fertile, viable female in a few, e.g., boas). ZW offspring are produced by endoreplication before meiosis or by central fusion. ZZ and WW offspring occur either by terminal fusion or by endomitosis in the egg cell.
In polyploid obligate parthenogens, like the whiptail lizard, all the offspring are female.
In many hymenopteran insects such as honeybees, female eggs are produced sexually, using sperm from a drone father, while the production of further drones (males) depends on the queen (and occasionally workers) producing unfertilized eggs. This means that females (workers and queens) are always diploid, while males (drones) are always haploid, and produced parthenogenetically.
Facultative
Facultative parthenogenesis occurs when a female can produce offspring either sexually or via asexual reproduction. Facultative parthenogenesis is extremely rare in nature, with only a few examples of animal taxa capable of facultative parthenogenesis. One of the best-known examples of taxa exhibiting facultative parthenogenesis are mayflies; presumably, this is the default reproductive mode of all species in this insect order. Facultative parthenogenesis has generally been believed to be a response to a lack of a viable male. A female may undergo facultative parthenogenesis if a male is absent from the habitat or if it is unable to produce viable offspring. However, California condors and the tropical lizard Lepidophyma smithii both can produce parthenogenic offspring in the presence of males, indicating that facultative parthenogenesis may be more common than previously thought and is not simply a response to a lack of males. | Parthenogenesis | Wikipedia | 472 | 9276466 | https://en.wikipedia.org/wiki/Parthenogenesis | Biology and health sciences | Biological reproduction | Biology |
In aphids, a generation sexually conceived by a male and a female produces only females. The reason for this is the non-random segregation of the sex chromosomes 'X' and 'O' during spermatogenesis.
Facultative parthenogenesis is often used to describe cases of spontaneous parthenogenesis in normally sexual animals. For example, many cases of spontaneous parthenogenesis in sharks, some snakes, Komodo dragons, and a variety of domesticated birds were widely attributed to facultative parthenogenesis. These cases are examples of spontaneous parthenogenesis. The occurrence of such asexually produced eggs in sexual animals can be explained by a meiotic error, leading to eggs produced via automixis.
Obligate
Obligate parthenogenesis is the process in which organisms exclusively reproduce through asexual means. Many species have transitioned to obligate parthenogenesis over evolutionary time. Well documented transitions to obligate parthenogenesis have been found in numerous metazoan taxa, albeit through highly diverse mechanisms. These transitions often occur as a result of inbreeding or mutation within large populations. Some documented species, specifically salamanders and geckos, that rely on obligate parthenogenesis as their major method of reproduction. As such, there are over 80 species of unisex reptiles (mostly lizards but including a single snake species), amphibians and fishes in nature for which males are no longer a part of the reproductive process. A female produces an ovum with a full set (two sets of genes) provided solely by the mother. Thus, a male is not needed to provide sperm to fertilize the egg. This form of asexual reproduction is thought in some cases to be a serious threat to biodiversity for the subsequent lack of gene variation and potentially decreased fitness of the offspring. | Parthenogenesis | Wikipedia | 387 | 9276466 | https://en.wikipedia.org/wiki/Parthenogenesis | Biology and health sciences | Biological reproduction | Biology |
Some invertebrate species that feature (partial) sexual reproduction in their native range are found to reproduce solely by parthenogenesis in areas to which they have been introduced. Relying solely on parthenogenetic reproduction has several advantages for an invasive species: it obviates the need for individuals in a very sparse initial population to search for mates; and an exclusively female sex distribution allows a population to multiply and invade more rapidly (potentially twice as fast). Examples include several aphid species and the willow sawfly, Nematus oligospilus, which is sexual in its native Holarctic habitat but parthenogenetic where it has been introduced into the Southern Hemisphere.
Natural occurrence
Parthenogenesis does not apply to isogamous species. Parthenogenesis occurs naturally in aphids, Daphnia, rotifers, nematodes, and some other invertebrates, as well as in many plants. Among vertebrates, strict parthenogenesis is only known to occur in lizards, snakes, birds, and sharks. Fish, amphibians, and reptiles make use of various forms of gynogenesis and hybridogenesis (an incomplete form of parthenogenesis). The first all-female (unisexual) reproduction in vertebrates was described in the fish Poecilia formosa in 1932. Since then at least 50 species of unisexual vertebrate have been described, including at least 20 fish, 25 lizards, a single snake species, frogs, and salamanders.
Artificial induction
Use of an electrical or chemical stimulus can produce the beginning of the process of parthenogenesis in the asexual development of viable offspring.
During oocyte development, high metaphase promoting factor (MPF) activity causes mammalian oocytes to arrest at the metaphase II stage until fertilization by a sperm. The fertilization event causes intracellular calcium oscillations, and targeted degradation of cyclin B, a regulatory subunit of MPF, thus permitting the MII-arrested oocyte to proceed through meiosis. | Parthenogenesis | Wikipedia | 431 | 9276466 | https://en.wikipedia.org/wiki/Parthenogenesis | Biology and health sciences | Biological reproduction | Biology |
To initiate unfertilised development of swine oocytes, various methods exist to induce an artificial activation that mimics sperm entry, such as calcium ionophore treatment, microinjection of calcium ions, or electrical stimulation. Treatment with cycloheximide, a non-specific protein synthesis inhibitor, enhances the development of unfertilised eggs in swine presumably by continual inhibition of MPF/cyclin B. As meiosis proceeds, extrusion of the second polar is blocked by exposure to cytochalasin B. This treatment results in a diploid (2 maternal genomes) parthenote The resulting embryos can be surgically transferred to a recipient oviduct for further development, but will succumb to developmental failure after ≈30 days of gestation. The swine placenta in these cases often appears hypo-vascular: see free image (Figure 1) in linked reference.
Induced parthenogenesis of this type in mice and monkeys results in abnormal development. This is because mammals have imprinted genetic regions, where either the maternal or the paternal chromosome is inactivated in the offspring for development to proceed normally. A mammal developing from parthenogenesis would have double doses of maternally imprinted genes and lack paternally imprinted genes, leading to developmental abnormalities. It has been suggested that defects in placental folding or interdigitation are one cause of swine parthenote abortive development. As a consequence, research on the induced development of unfertilised eggs in humans is focused on the production of embryonic stem cells for use in medical treatment, not as a reproductive strategy.
In 2022, researchers reported that they have produced viable offspring born from unfertilized eggs in mice, addressing the problems of genomic imprinting by "targeted DNA methylation rewriting of seven imprinting control regions".
In humans | Parthenogenesis | Wikipedia | 389 | 9276466 | https://en.wikipedia.org/wiki/Parthenogenesis | Biology and health sciences | Biological reproduction | Biology |
In 1955, Helen Spurway, a geneticist specializing in the reproductive biology of the guppy (Lebistes reticulatus), claimed that parthenogenesis may occur (though very rarely) in humans, leading to so-called "virgin births". This created some sensation among her colleagues and the lay public alike. Sometimes an embryo may begin to divide without fertilization, but it cannot fully develop on its own; so while it may create some skin and nerve cells, it cannot create others (such as skeletal muscle) and becomes a type of benign tumor called an ovarian teratoma. Spontaneous ovarian activation is not rare and has been known about since the 19th century. Some teratomas can even become primitive fetuses (fetiform teratoma) with imperfect heads, limbs and other structures, but are non-viable.
In 1995, there was a reported case of partial human parthenogenesis; a boy was found to have some of his cells (such as white blood cells) to be lacking in any genetic content from his father. Scientists believe that an unfertilized egg began to self-divide but then had some (but not all) of its cells fertilized by a sperm cell; this must have happened early in development, as self-activated eggs quickly lose their ability to be fertilized. The unfertilized cells eventually duplicated their DNA, boosting their chromosomes to 46. When the unfertilized cells hit a developmental block, the fertilized cells took over and developed that tissue. The boy had asymmetrical facial features and learning difficulties but was otherwise healthy. This would make him a parthenogenetic chimera (a child with two cell lineages in his body). While over a dozen similar cases have been reported since then (usually discovered after the patient demonstrated clinical abnormalities), there have been no scientifically confirmed reports of a non-chimeric, clinically healthy human parthenote (i.e. produced from a single, parthenogenetic-activated oocyte). | Parthenogenesis | Wikipedia | 429 | 9276466 | https://en.wikipedia.org/wiki/Parthenogenesis | Biology and health sciences | Biological reproduction | Biology |
In 2007, the International Stem Cell Corporation of California announced that Elena Revazova had intentionally created human stem cells from unfertilized human eggs using parthenogenesis. The process may offer a way for creating stem cells genetically matched to a particular female to treat degenerative diseases. The same year, Revazova and ISCC published an article describing how to produce human stem cells that are homozygous in the HLA region of DNA. These stem cells are called HLA homozygous parthenogenetic human stem cells (hpSC-Hhom) and would allow derivatives of these cells to be implanted without immune rejection. With selection of oocyte donors according to HLA haplotype, it would be possible to generate a bank of cell lines whose tissue derivatives, collectively, could be MHC-matched with a significant number of individuals within the human population.
After an independent investigation, it was revealed that the discredited South Korean scientist Hwang Woo-Suk unknowingly produced the first human embryos resulting from parthenogenesis. Initially, Hwang claimed he and his team had extracted stem cells from cloned human embryos, a result later found to be fabricated. Further examination of the chromosomes of these cells show indicators of parthenogenesis in those extracted stem cells, similar to those found in the mice created by Tokyo scientists in 2004. Although Hwang deceived the world about being the first to create artificially cloned human embryos, he contributed a major breakthrough to stem cell research by creating human embryos using parthenogenesis.
Similar phenomena
Gynogenesis | Parthenogenesis | Wikipedia | 331 | 9276466 | https://en.wikipedia.org/wiki/Parthenogenesis | Biology and health sciences | Biological reproduction | Biology |
A form of asexual reproduction related to parthenogenesis is gynogenesis. Here, offspring are produced by the same mechanism as in parthenogenesis, but with the requirement that the egg merely be stimulated by the presence of sperm in order to develop. However, the sperm cell does not contribute any genetic material to the offspring. Since gynogenetic species are all female, activation of their eggs requires mating with males of a closely related species for the needed stimulus. Some salamanders of the genus Ambystoma are gynogenetic and appear to have been so for over a million years. The success of those salamanders may be due to rare fertilization of eggs by males, introducing new material to the gene pool, which may result from perhaps only one mating out of a million. In addition, the Amazon molly is known to reproduce by gynogenesis.
Hybridogenesis
Hybridogenesis is a mode of reproduction of hybrids. Hybridogenetic hybrids (for example AB genome), usually females, during gametogenesis exclude one of parental genomes (A) and produce gametes with unrecombined genome of second parental species (B), instead of containing mixed recombined parental genomes. First genome (A) is restored by fertilization of these gametes with gametes from the first species (AA, sexual host, usually male). Hybridogenesis is not completely asexual, but hemiclonal: half the genome is passed to the next generation clonally, unrecombined, intact (B), other half sexually, recombined (A). This process continues, so that each generation is half (or hemi-) clonal on the mother's side and has half new genetic material from the father's side.
This form of reproduction is seen in some live-bearing fish of the genus Poeciliopsis as well as in some of the Pelophylax spp. ("green frogs" or "waterfrogs"):
P. kl. esculentus (edible frog): P. lessonae × P. ridibundus,
P. kl. grafi (Graf's hybrid frog): P. perezi × P. ridibundus
P. kl. hispanicus (Italian edible frog) – unknown origin: P. bergeri × P. ridibundus or P. kl. esculentus | Parthenogenesis | Wikipedia | 510 | 9276466 | https://en.wikipedia.org/wiki/Parthenogenesis | Biology and health sciences | Biological reproduction | Biology |
Other examples where hybridogenesis is at least one of modes of reproduction include i.e.
Iberian minnow Tropidophoxinellus alburnoides (Squalius pyrenaicus × hypothetical ancestor related with Anaecypris hispanica)
spined loaches Cobitis hankugensis × C. longicorpus
Bacillus stick insects B. rossius × Bacillus grandii benazzii
In human culture
Parthenogenesis, in the form of reproduction from a single individual (typically a god), is common in mythology, religion, and folklore around the world, including in ancient Greek myth; for example, Athena was born from the head of Zeus. In Christianity and Islam, there is the virgin birth of Jesus; there are stories of miraculous births in other religions including Islam.
The theme is one of several aspects of reproductive biology explored in science fiction. | Parthenogenesis | Wikipedia | 183 | 9276466 | https://en.wikipedia.org/wiki/Parthenogenesis | Biology and health sciences | Biological reproduction | Biology |
Fault blocks are very large blocks of rock, sometimes hundreds of kilometres in extent, created by tectonic and localized stresses in Earth's crust. Large areas of bedrock are broken up into blocks by faults. Blocks are characterized by relatively uniform lithology. The largest of these fault blocks are called crustal blocks. Large crustal blocks broken off from tectonic plates are called terranes. Those terranes which are the full thickness of the lithosphere are called microplates. Continent-sized blocks are called variously microcontinents, continental ribbons, H-blocks, extensional allochthons and outer highs.
Because most stresses relate to the tectonic activity of moving plates, most motion between blocks is horizontal, that is parallel to the Earth's crust by strike-slip faults. However vertical movement of blocks produces much more dramatic results. Landforms (mountains, hills, ridges, lakes, valleys, etc.) are sometimes formed when the faults have a large vertical displacement. Adjacent raised blocks (horsts) and down-dropped blocks (grabens) can form high escarpments. Often the movement of these blocks is accompanied by tilting, due to compaction or stretching of the crust at that point.
Fault-block mountains
Fault-block mountains often result from rifting, an indicator of extensional tectonics. These can be small or form extensive rift valley systems, such as the East African Rift zone. Death Valley in California is a smaller example. There are two main types of block mountains; uplifted blocks between two faults and tilted blocks mainly controlled by one fault.
Lifted type block mountains have two steep sides exposing both sides scarps, leading to the horst and graben terrain seen in various parts of Europe including the Upper Rhine valley, a graben between two horsts – the Vosges mountains (in France) and the Black Forest (in Germany), and also the Rila – Rhodope Massif in Bulgaria, Southeast Europe, including the well defined horsts of Belasitsa (linear horst), Rila mountain (vaulted domed shaped horst) and Pirin mountain – a horst forming a massive anticline situated between the complex graben valleys of Struma and that of Mesta.
Tilted type block mountains have one gently sloping side and one steep side with an exposed scarp, and are common in the Basin and Range region of the western United States. | Fault block | Wikipedia | 493 | 5470669 | https://en.wikipedia.org/wiki/Fault%20block | Physical sciences | Montane landforms | Earth science |
An example of a graben is the basin of the Narmada River in India, between the Vindhya and Satpura horsts. | Fault block | Wikipedia | 29 | 5470669 | https://en.wikipedia.org/wiki/Fault%20block | Physical sciences | Montane landforms | Earth science |
The near side of the Moon is the lunar hemisphere that always faces towards Earth, opposite to the far side. Only one side of the Moon is visible from Earth because the Moon rotates on its axis at the same rate that the Moon orbits the Earth—a situation known as tidal locking.
The Moon is directly illuminated by the Sun, and the cyclically varying viewing conditions cause the lunar phases. Sometimes the dark portion of the Moon is faintly visible due to earthshine, which is indirect sunlight reflected from the surface of Earth and onto the Moon.
Since the Moon's orbit is both somewhat elliptical and inclined to its equatorial plane, libration allows up to 59% of the Moon's surface to be viewed from Earth (though only half at any moment from any point).
Orientation
The image of the Moon here is drawn as is normally shown on maps, that is with north on top and west to the left. Astronomers traditionally turn the map to have south on top to correspond with the northern-hemisphere view in astronomical telescopes, which typically show the image upside down.
West and east on the Moon are where they would be expected, when standing on the Moon. But when the Moon is seen from Earth, then the east–west direction is reversed. When specifying coordinates on the Moon it should therefore always be mentioned whether geographic (or rather selenographic) coordinates are used or astronomical coordinates.
The Moon's actual orientation in Earth's sky or on the horizon depends on the viewers geographic latitude on Earth. In the following description a few typical cases will be considered. | Near side of the Moon | Wikipedia | 318 | 5473867 | https://en.wikipedia.org/wiki/Near%20side%20of%20the%20Moon | Physical sciences | Solar System | Astronomy |
On the north pole, if the Moon is visible, it stands low above the horizon with its north pole up.
In mid northern latitudes (North America, Europe, Asia) the Moon rises in the east with its northeastern limb up (Mare Crisium), it reaches its highest point in the south with its north on top, and sets in the west with its northwestern limb (Mare Imbrium) on top.
On the equator, when the Moon rises in the east, its N — S axis appears horizontal and Mare Foecunditatis is on top. When it sets in the west, about 12.5 hours later, the axis is still horizontal, and Oceanus Procellarum is the last area to dip below the horizon. In between these events, the Moon reached its highest point in the zenith and then its selenographic directions are lined up with those on Earth.
In mid southern latitudes (South America, South Pacific, Australia, South Africa) the Moon rises in the east with its southeastern limb up (Mare Nectaris), it reaches its highest point in the north with its south on top, and sets in the west with its southwestern limb (Mare Humorum) on top.
On the south pole the Moon behaves as on the north pole, but there it appears with its south pole up.
Differences | Near side of the Moon | Wikipedia | 272 | 5473867 | https://en.wikipedia.org/wiki/Near%20side%20of%20the%20Moon | Physical sciences | Solar System | Astronomy |
The two hemispheres have distinctly different appearances, with the near side covered in multiple, large maria (Latin for 'seas'). These lowlands were believed to be seas of lunar water by the astronomers who first mapped them, in the 17th century (notably, Giovanni Battista Riccioli and Francesco Maria Grimaldi). Although no bodies of liquid exist on the Moon, the term "mare" (plural: maria) is still used. The far side has a battered, densely cratered appearance with few maria. Only 1% of the surface of the far side is covered by maria, compared to 31.2% on the near side. According to research analyzed by NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission, the reason for the difference is because the Moon's crust is thinner on the near side compared to the far side. The dark splotches that make up the large lunar maria are lava-filled impact basins that were created by asteroid impacts about four billion years ago. Though both sides of the Moon were bombarded by similarly large impactors, the near side hemisphere crust and upper mantle was hotter than that of the far side, resulting in the larger impact craters. These larger impact craters make up the Man in the Moon references from popular mythology. | Near side of the Moon | Wikipedia | 257 | 5473867 | https://en.wikipedia.org/wiki/Near%20side%20of%20the%20Moon | Physical sciences | Solar System | Astronomy |
In quantum physics, a measurement is the testing or manipulation of a physical system to yield a numerical result. A fundamental feature of quantum theory is that the predictions it makes are probabilistic. The procedure for finding a probability involves combining a quantum state, which mathematically describes a quantum system, with a mathematical representation of the measurement to be performed on that system. The formula for this calculation is known as the Born rule. For example, a quantum particle like an electron can be described by a quantum state that associates to each point in space a complex number called a probability amplitude. Applying the Born rule to these amplitudes gives the probabilities that the electron will be found in one region or another when an experiment is performed to locate it. This is the best the theory can do; it cannot say for certain where the electron will be found. The same quantum state can also be used to make a prediction of how the electron will be moving, if an experiment is performed to measure its momentum instead of its position. The uncertainty principle implies that, whatever the quantum state, the range of predictions for the electron's position and the range of predictions for its momentum cannot both be narrow. Some quantum states imply a near-certain prediction of the result of a position measurement, but the result of a momentum measurement will be highly unpredictable, and vice versa. Furthermore, the fact that nature violates the statistical conditions known as Bell inequalities indicates that the unpredictability of quantum measurement results cannot be explained away as due to ignorance about "local hidden variables" within quantum systems.
Measuring a quantum system generally changes the quantum state that describes that system. This is a central feature of quantum mechanics, one that is both mathematically intricate and conceptually subtle. The mathematical tools for making predictions about what measurement outcomes may occur, and how quantum states can change, were developed during the 20th century and make use of linear algebra and functional analysis. Quantum physics has proven to be an empirical success and to have wide-ranging applicability. However, on a more philosophical level, debates continue about the meaning of the measurement concept.
Mathematical formalism
"Observables" as self-adjoint operators | Measurement in quantum mechanics | Wikipedia | 442 | 573875 | https://en.wikipedia.org/wiki/Measurement%20in%20quantum%20mechanics | Physical sciences | Quantum mechanics | Physics |
In quantum mechanics, each physical system is associated with a Hilbert space, each element of which represents a possible state of the physical system. The approach codified by John von Neumann represents a measurement upon a physical system by a self-adjoint operator on that Hilbert space termed an "observable". These observables play the role of measurable quantities familiar from classical physics: position, momentum, energy, angular momentum and so on. The dimension of the Hilbert space may be infinite, as it is for the space of square-integrable functions on a line, which is used to define the quantum physics of a continuous degree of freedom. Alternatively, the Hilbert space may be finite-dimensional, as occurs for spin degrees of freedom. Many treatments of the theory focus on the finite-dimensional case, as the mathematics involved is somewhat less demanding. Indeed, introductory physics texts on quantum mechanics often gloss over mathematical technicalities that arise for continuous-valued observables and infinite-dimensional Hilbert spaces, such as the distinction between bounded and unbounded operators; questions of convergence (whether the limit of a sequence of Hilbert-space elements also belongs to the Hilbert space), exotic possibilities for sets of eigenvalues, like Cantor sets; and so forth. These issues can be satisfactorily resolved using spectral theory; the present article will avoid them whenever possible.
Projective measurement
The eigenvectors of a von Neumann observable form an orthonormal basis for the Hilbert space, and each possible outcome of that measurement corresponds to one of the vectors comprising the basis. A density operator is a positive-semidefinite operator on the Hilbert space whose trace is equal to 1. For each measurement that can be defined, the probability distribution over the outcomes of that measurement can be computed from the density operator. The procedure for doing so is the Born rule, which states that
where is the density operator, and is the projection operator onto the basis vector corresponding to the measurement outcome . The average of the eigenvalues of a von Neumann observable, weighted by the Born rule probabilities, is the expectation value of that observable. For an observable , the expectation value given a quantum state is | Measurement in quantum mechanics | Wikipedia | 456 | 573875 | https://en.wikipedia.org/wiki/Measurement%20in%20quantum%20mechanics | Physical sciences | Quantum mechanics | Physics |
A density operator that is a rank-1 projection is known as a pure quantum state, and all quantum states that are not pure are designated mixed. Pure states are also known as wavefunctions. Assigning a pure state to a quantum system implies certainty about the outcome of some measurement on that system (i.e., for some outcome ). Any mixed state can be written as a convex combination of pure states, though not in a unique way. The state space of a quantum system is the set of all states, pure and mixed, that can be assigned to it.
The Born rule associates a probability with each unit vector in the Hilbert space, in such a way that these probabilities sum to 1 for any set of unit vectors comprising an orthonormal basis. Moreover, the probability associated with a unit vector is a function of the density operator and the unit vector, and not of additional information like a choice of basis for that vector to be embedded in. Gleason's theorem establishes the converse: all assignments of probabilities to unit vectors (or, equivalently, to the operators that project onto them) that satisfy these conditions take the form of applying the Born rule to some density operator.
Generalized measurement (POVM)
In functional analysis and quantum measurement theory, a positive-operator-valued measure (POVM) is a measure whose values are positive semi-definite operators on a Hilbert space. POVMs are a generalisation of projection-valued measures (PVMs) and, correspondingly, quantum measurements described by POVMs are a generalisation of quantum measurement described by PVMs. In rough analogy, a POVM is to a PVM what a mixed state is to a pure state. Mixed states are needed to specify the state of a subsystem of a larger system (see Schrödinger–HJW theorem); analogously, POVMs are necessary to describe the effect on a subsystem of a projective measurement performed on a larger system. POVMs are the most general kind of measurement in quantum mechanics, and can also be used in quantum field theory. They are extensively used in the field of quantum information.
In the simplest case, of a POVM with a finite number of elements acting on a finite-dimensional Hilbert space, a POVM is a set of positive semi-definite matrices on a Hilbert space that sum to the identity matrix, | Measurement in quantum mechanics | Wikipedia | 498 | 573875 | https://en.wikipedia.org/wiki/Measurement%20in%20quantum%20mechanics | Physical sciences | Quantum mechanics | Physics |
In quantum mechanics, the POVM element is associated with the measurement outcome , such that the probability of obtaining it when making a measurement on the quantum state is given by
,
where is the trace operator. When the quantum state being measured is a pure state this formula reduces to
.
State change due to measurement
A measurement upon a quantum system will generally bring about a change of the quantum state of that system. Writing a POVM does not provide the complete information necessary to describe this state-change process. To remedy this, further information is specified by decomposing each POVM element into a product:
The Kraus operators , named for Karl Kraus, provide a specification of the state-change process. They are not necessarily self-adjoint, but the products are. If upon performing the measurement the outcome is obtained, then the initial state is updated to
An important special case is the Lüders rule, named for Gerhart Lüders. If the POVM is itself a PVM, then the Kraus operators can be taken to be the projectors onto the eigenspaces of the von Neumann observable:
If the initial state is pure, and the projectors have rank 1, they can be written as projectors onto the vectors and , respectively. The formula simplifies thus to
Lüders rule has historically been known as the "reduction of the wave packet" or the "collapse of the wavefunction". The pure state implies a probability-one prediction for any von Neumann observable that has as an eigenvector. Introductory texts on quantum theory often express this by saying that if a quantum measurement is repeated in quick succession, the same outcome will occur both times. This is an oversimplification, since the physical implementation of a quantum measurement may involve a process like the absorption of a photon; after the measurement, the photon does not exist to be measured again.
We can define a linear, trace-preserving, completely positive map, by summing over all the possible post-measurement states of a POVM without the normalisation:
It is an example of a quantum channel, and can be interpreted as expressing how a quantum state changes if a measurement is performed but the result of that measurement is lost.
Examples | Measurement in quantum mechanics | Wikipedia | 459 | 573875 | https://en.wikipedia.org/wiki/Measurement%20in%20quantum%20mechanics | Physical sciences | Quantum mechanics | Physics |
The prototypical example of a finite-dimensional Hilbert space is a qubit, a quantum system whose Hilbert space is 2-dimensional. A pure state for a qubit can be written as a linear combination of two orthogonal basis states and with complex coefficients:
A measurement in the basis will yield outcome with probability and outcome with probability , so by normalization,
An arbitrary state for a qubit can be written as a linear combination of the Pauli matrices, which provide a basis for self-adjoint matrices:
where the real numbers are the coordinates of a point within the unit ball and
POVM elements can be represented likewise, though the trace of a POVM element is not fixed to equal 1. The Pauli matrices are traceless and orthogonal to one another with respect to the Hilbert–Schmidt inner product, and so the coordinates of the state are the expectation values of the three von Neumann measurements defined by the Pauli matrices. If such a measurement is applied to a qubit, then by the Lüders rule, the state will update to the eigenvector of that Pauli matrix corresponding to the measurement outcome. The eigenvectors of are the basis states and , and a measurement of is often called a measurement in the "computational basis." After a measurement in the computational basis, the outcome of a or measurement is maximally uncertain.
A pair of qubits together form a system whose Hilbert space is 4-dimensional. One significant von Neumann measurement on this system is that defined by the Bell basis, a set of four maximally entangled states:
A common and useful example of quantum mechanics applied to a continuous degree of freedom is the quantum harmonic oscillator. This system is defined by the Hamiltonian
where , the momentum operator and the position operator are self-adjoint operators on the Hilbert space of square-integrable functions on the real line. The energy eigenstates solve the time-independent Schrödinger equation:
These eigenvalues can be shown to be given by
and these values give the possible numerical outcomes of an energy measurement upon the oscillator. The set of possible outcomes of a position measurement on a harmonic oscillator is continuous, and so predictions are stated in terms of a probability density function that gives the probability of the measurement outcome lying in the infinitesimal interval from to .
History of the measurement concept
The "old quantum theory" | Measurement in quantum mechanics | Wikipedia | 491 | 573875 | https://en.wikipedia.org/wiki/Measurement%20in%20quantum%20mechanics | Physical sciences | Quantum mechanics | Physics |
The old quantum theory is a collection of results from the years 1900–1925 which predate modern quantum mechanics. The theory was never complete or self-consistent, but was rather a set of heuristic corrections to classical mechanics. The theory is now understood as a semi-classical approximation to modern quantum mechanics. Notable results from this period include Planck's calculation of the blackbody radiation spectrum, Einstein's explanation of the photoelectric effect, Einstein and Debye's work on the specific heat of solids, Bohr and van Leeuwen's proof that classical physics cannot account for diamagnetism, Bohr's model of the hydrogen atom and Arnold Sommerfeld's extension of the Bohr model to include relativistic effects.
The Stern–Gerlach experiment, proposed in 1921 and implemented in 1922, became a prototypical example of a quantum measurement having a discrete set of possible outcomes. In the original experiment, silver atoms were sent through a spatially varying magnetic field, which deflected them before they struck a detector screen, such as a glass slide. Particles with non-zero magnetic moment are deflected, due to the magnetic field gradient, from a straight path. The screen reveals discrete points of accumulation, rather than a continuous distribution, owing to the particles' quantized spin.
Transition to the “new” quantum theory
A 1925 paper by Heisenberg, known in English as "Quantum theoretical re-interpretation of kinematic and mechanical relations", marked a pivotal moment in the maturation of quantum physics. Heisenberg sought to develop a theory of atomic phenomena that relied only on "observable" quantities. At the time, and in contrast with the later standard presentation of quantum mechanics, Heisenberg did not regard the position of an electron bound within an atom as "observable". Instead, his principal quantities of interest were the frequencies of light emitted or absorbed by atoms.
The uncertainty principle dates to this period. It is frequently attributed to Heisenberg, who introduced the concept in analyzing a thought experiment where one attempts to measure an electron's position and momentum simultaneously. However, Heisenberg did not give precise mathematical definitions of what the "uncertainty" in these measurements meant. The precise mathematical statement of the position-momentum uncertainty principle is due to Kennard, Pauli, and Weyl, and its generalization to arbitrary pairs of noncommuting observables is due to Robertson and Schrödinger. | Measurement in quantum mechanics | Wikipedia | 508 | 573875 | https://en.wikipedia.org/wiki/Measurement%20in%20quantum%20mechanics | Physical sciences | Quantum mechanics | Physics |
Writing and for the self-adjoint operators representing position and momentum respectively, a standard deviation of position can be defined as
and likewise for the momentum:
The Kennard–Pauli–Weyl uncertainty relation is
This inequality means that no preparation of a quantum particle can imply simultaneously precise predictions for a measurement of position and for a measurement of momentum. The Robertson inequality generalizes this to the case of an arbitrary pair of self-adjoint operators and . The commutator of these two operators is
and this provides the lower bound on the product of standard deviations:
Substituting in the canonical commutation relation , an expression first postulated by Max Born in 1925, recovers the Kennard–Pauli–Weyl statement of the uncertainty principle.
From uncertainty to no-hidden-variables
The existence of the uncertainty principle naturally raises the question of whether quantum mechanics can be understood as an approximation to a more exact theory. Do there exist "hidden variables", more fundamental than the quantities addressed in quantum theory itself, knowledge of which would allow more exact predictions than quantum theory can provide? A collection of results, most significantly Bell's theorem, have demonstrated that broad classes of such hidden-variable theories are in fact incompatible with quantum physics.
Bell published the theorem now known by his name in 1964, investigating more deeply a thought experiment originally proposed in 1935 by Einstein, Podolsky and Rosen. According to Bell's theorem, if nature actually operates in accord with any theory of local hidden variables, then the results of a Bell test will be constrained in a particular, quantifiable way. If a Bell test is performed in a laboratory and the results are not thus constrained, then they are inconsistent with the hypothesis that local hidden variables exist. Such results would support the position that there is no way to explain the phenomena of quantum mechanics in terms of a more fundamental description of nature that is more in line with the rules of classical physics. Many types of Bell test have been performed in physics laboratories, often with the goal of ameliorating problems of experimental design or set-up that could in principle affect the validity of the findings of earlier Bell tests. This is known as "closing loopholes in Bell tests". To date, Bell tests have found that the hypothesis of local hidden variables is inconsistent with the way that physical systems behave. | Measurement in quantum mechanics | Wikipedia | 473 | 573875 | https://en.wikipedia.org/wiki/Measurement%20in%20quantum%20mechanics | Physical sciences | Quantum mechanics | Physics |
Quantum systems as measuring devices
The Robertson–Schrödinger uncertainty principle establishes that when two observables do not commute, there is a tradeoff in predictability between them. The Wigner–Araki–Yanase theorem demonstrates another consequence of non-commutativity: the presence of a conservation law limits the accuracy with which observables that fail to commute with the conserved quantity can be measured. Further investigation in this line led to the formulation of the Wigner–Yanase skew information.
Historically, experiments in quantum physics have often been described in semiclassical terms. For example, the spin of an atom in a Stern–Gerlach experiment might be treated as a quantum degree of freedom, while the atom is regarded as moving through a magnetic field described by the classical theory of Maxwell's equations. But the devices used to build the experimental apparatus are themselves physical systems, and so quantum mechanics should be applicable to them as well. Beginning in the 1950s, Rosenfeld, von Weizsäcker and others tried to develop consistency conditions that expressed when a quantum-mechanical system could be treated as a measuring apparatus. One proposal for a criterion regarding when a system used as part of a measuring device can be modeled semiclassically relies on the Wigner function, a quasiprobability distribution that can be treated as a probability distribution on phase space in those cases where it is everywhere non-negative.
Decoherence
A quantum state for an imperfectly isolated system will generally evolve to be entangled with the quantum state for the environment. Consequently, even if the system's initial state is pure, the state at a later time, found by taking the partial trace of the joint system-environment state, will be mixed. This phenomenon of entanglement produced by system-environment interactions tends to obscure the more exotic features of quantum mechanics that the system could in principle manifest. Quantum decoherence, as this effect is known, was first studied in detail during the 1970s. (Earlier investigations into how classical physics might be obtained as a limit of quantum mechanics had explored the subject of imperfectly isolated systems, but the role of entanglement was not fully appreciated.) A significant portion of the effort involved in quantum computing is to avoid the deleterious effects of decoherence. | Measurement in quantum mechanics | Wikipedia | 467 | 573875 | https://en.wikipedia.org/wiki/Measurement%20in%20quantum%20mechanics | Physical sciences | Quantum mechanics | Physics |
To illustrate, let denote the initial state of the system, the initial state of the environment and the Hamiltonian specifying the system-environment interaction. The density operator can be diagonalized and written as a linear combination of the projectors onto its eigenvectors:
Expressing time evolution for a duration by the unitary operator , the state for the system after this evolution is
which evaluates to
The quantities surrounding can be identified as Kraus operators, and so this defines a quantum channel.
Specifying a form of interaction between system and environment can establish a set of "pointer states," states for the system that are (approximately) stable, apart from overall phase factors, with respect to environmental fluctuations. A set of pointer states defines a preferred orthonormal basis for the system's Hilbert space.
Quantum information and computation
Quantum information science studies how information science and its application as technology depend on quantum-mechanical phenomena. Understanding measurement in quantum physics is important for this field in many ways, some of which are briefly surveyed here.
Measurement, entropy, and distinguishability
The von Neumann entropy is a measure of the statistical uncertainty represented by a quantum state. For a density matrix , the von Neumann entropy is
writing in terms of its basis of eigenvectors,
the von Neumann entropy is
This is the Shannon entropy of the set of eigenvalues interpreted as a probability distribution, and so the von Neumann entropy is the Shannon entropy of the random variable defined by measuring in the eigenbasis of . Consequently, the von Neumann entropy vanishes when is pure. The von Neumann entropy of can equivalently be characterized as the minimum Shannon entropy for a measurement given the quantum state , with the minimization over all POVMs with rank-1 elements.
Many other quantities used in quantum information theory also find motivation and justification in terms of measurements. For example, the trace distance between quantum states is equal to the largest difference in probability that those two quantum states can imply for a measurement outcome:
Similarly, the fidelity of two quantum states, defined by
expresses the probability that one state will pass a test for identifying a successful preparation of the other. The trace distance provides bounds on the fidelity via the Fuchs–van de Graaf inequalities:
Quantum circuits | Measurement in quantum mechanics | Wikipedia | 455 | 573875 | https://en.wikipedia.org/wiki/Measurement%20in%20quantum%20mechanics | Physical sciences | Quantum mechanics | Physics |
Quantum circuits are a model for quantum computation in which a computation is a sequence of quantum gates followed by measurements. The gates are reversible transformations on a quantum mechanical analog of an n-bit register. This analogous structure is referred to as an n-qubit register. Measurements, drawn on a circuit diagram as stylized pointer dials, indicate where and how a result is obtained from the quantum computer after the steps of the computation are executed. Without loss of generality, one can work with the standard circuit model, in which the set of gates are single-qubit unitary transformations and controlled NOT gates on pairs of qubits, and all measurements are in the computational basis.
Measurement-based quantum computation
Measurement-based quantum computation (MBQC) is a model of quantum computing in which the answer to a question is, informally speaking, created in the act of measuring the physical system that serves as the computer.
Quantum tomography
Quantum state tomography is a process by which, given a set of data representing the results of quantum measurements, a quantum state consistent with those measurement results is computed. It is named by analogy with tomography, the reconstruction of three-dimensional images from slices taken through them, as in a CT scan. Tomography of quantum states can be extended to tomography of quantum channels and even of measurements.
Quantum metrology
Quantum metrology is the use of quantum physics to aid the measurement of quantities that, generally, had meaning in classical physics, such as exploiting quantum effects to increase the precision with which a length can be measured. A celebrated example is the introduction of squeezed light into the LIGO experiment, which increased its sensitivity to gravitational waves.
Laboratory implementations
The range of physical procedures to which the mathematics of quantum measurement can be applied is very broad. In the early years of the subject, laboratory procedures involved the recording of spectral lines, the darkening of photographic film, the observation of scintillations, finding tracks in cloud chambers, and hearing clicks from Geiger counters. Language from this era persists, such as the description of measurement outcomes in the abstract as "detector clicks". | Measurement in quantum mechanics | Wikipedia | 426 | 573875 | https://en.wikipedia.org/wiki/Measurement%20in%20quantum%20mechanics | Physical sciences | Quantum mechanics | Physics |
The double-slit experiment is a prototypical illustration of quantum interference, typically described using electrons or photons. The first interference experiment to be carried out in a regime where both wave-like and particle-like aspects of photon behavior are significant was G. I. Taylor's test in 1909. Taylor used screens of smoked glass to attenuate the light passing through his apparatus, to the extent that, in modern language, only one photon would be illuminating the interferometer slits at a time. He recorded the interference patterns on photographic plates; for the dimmest light, the exposure time required was roughly three months. In 1974, the Italian physicists Pier Giorgio Merli, Gian Franco Missiroli, and Giulio Pozzi implemented the double-slit experiment using single electrons and a television tube. A quarter-century later, a team at the University of Vienna performed an interference experiment with buckyballs, in which the buckyballs that passed through the interferometer were ionized by a laser, and the ions then induced the emission of electrons, emissions which were in turn amplified and detected by an electron multiplier.
Modern quantum optics experiments can employ single-photon detectors. For example, in the "BIG Bell test" of 2018, several of the laboratory setups used single-photon avalanche diodes. Another laboratory setup used superconducting qubits. The standard method for performing measurements upon superconducting qubits is to couple a qubit with a resonator in such a way that the characteristic frequency of the resonator shifts according to the state for the qubit, and detecting this shift by observing how the resonator reacts to a probe signal.
Interpretations of quantum mechanics
Despite the consensus among scientists that quantum physics is in practice a successful theory, disagreements persist on a more philosophical level. Many debates in the area known as quantum foundations concern the role of measurement in quantum mechanics. Recurring questions include which interpretation of probability theory is best suited for the probabilities calculated from the Born rule; and whether the apparent randomness of quantum measurement outcomes is fundamental, or a consequence of a deeper deterministic process. Worldviews that present answers to questions like these are known as "interpretations" of quantum mechanics; as the physicist N. David Mermin once quipped, "New interpretations appear every year. None ever disappear." | Measurement in quantum mechanics | Wikipedia | 481 | 573875 | https://en.wikipedia.org/wiki/Measurement%20in%20quantum%20mechanics | Physical sciences | Quantum mechanics | Physics |
A central concern within quantum foundations is the "quantum measurement problem," though how this problem is delimited, and whether it should be counted as one question or multiple separate issues, are contested topics. Of primary interest is the seeming disparity between apparently distinct types of time evolution. Von Neumann declared that quantum mechanics contains "two fundamentally different types" of quantum-state change. First, there are those changes involving a measurement process, and second, there is unitary time evolution in the absence of measurement. The former is stochastic and discontinuous, writes von Neumann, and the latter deterministic and continuous. This dichotomy has set the tone for much later debate. Some interpretations of quantum mechanics find the reliance upon two different types of time evolution distasteful and regard the ambiguity of when to invoke one or the other as a deficiency of the way quantum theory was historically presented. To bolster these interpretations, their proponents have worked to derive ways of regarding "measurement" as a secondary concept and deducing the seemingly stochastic effect of measurement processes as approximations to more fundamental deterministic dynamics. However, consensus has not been achieved among proponents of the correct way to implement this program, and in particular how to justify the use of the Born rule to calculate probabilities. Other interpretations regard quantum states as statistical information about quantum systems, thus asserting that abrupt and discontinuous changes of quantum states are not problematic, simply reflecting updates of the available information. Of this line of thought, Bell asked, "Whose information? Information about what?" Answers to these questions vary among proponents of the informationally-oriented interpretations. | Measurement in quantum mechanics | Wikipedia | 338 | 573875 | https://en.wikipedia.org/wiki/Measurement%20in%20quantum%20mechanics | Physical sciences | Quantum mechanics | Physics |
In physics, circular motion is movement of an object along the circumference of a circle or rotation along a circular arc. It can be uniform, with a constant rate of rotation and constant tangential speed, or non-uniform with a changing rate of rotation. The rotation around a fixed axis of a three-dimensional body involves the circular motion of its parts. The equations of motion describe the movement of the center of mass of a body, which remains at a constant distance from the axis of rotation. In circular motion, the distance between the body and a fixed point on its surface remains the same, i.e., the body is assumed rigid.
Examples of circular motion include: special satellite orbits around the Earth (circular orbits), a ceiling fan's blades rotating around a hub, a stone that is tied to a rope and is being swung in circles, a car turning through a curve in a race track, an electron moving perpendicular to a uniform magnetic field, and a gear turning inside a mechanism.
Since the object's velocity vector is constantly changing direction, the moving object is undergoing acceleration by a centripetal force in the direction of the center of rotation. Without this acceleration, the object would move in a straight line, according to Newton's laws of motion.
Uniform circular motion
In physics, uniform circular motion describes the motion of a body traversing a circular path at a constant speed. Since the body describes circular motion, its distance from the axis of rotation remains constant at all times. Though the body's speed is constant, its velocity is not constant: velocity, a vector quantity, depends on both the body's speed and its direction of travel. This changing velocity indicates the presence of an acceleration; this centripetal acceleration is of constant magnitude and directed at all times toward the axis of rotation. This acceleration is, in turn, produced by a centripetal force which is also constant in magnitude and directed toward the axis of rotation.
In the case of rotation around a fixed axis of a rigid body that is not negligibly small compared to the radius of the path, each particle of the body describes a uniform circular motion with the same angular velocity, but with velocity and acceleration varying with the position with respect to the axis.
Formula
For motion in a circle of radius , the circumference of the circle is . If the period for one rotation is , the angular rate of rotation, also known as angular velocity, is:
and the units are radians/second. | Circular motion | Wikipedia | 512 | 574544 | https://en.wikipedia.org/wiki/Circular%20motion | Physical sciences | Classical mechanics | Physics |
The speed of the object traveling the circle is:
The angle swept out in a time is:
The angular acceleration, , of the particle is:
In the case of uniform circular motion, will be zero.
The acceleration due to change in the direction is:
The centripetal and centrifugal force can also be found using acceleration:
The vector relationships are shown in Figure 1. The axis of rotation is shown as a vector perpendicular to the plane of the orbit and with a magnitude . The direction of is chosen using the right-hand rule. With this convention for depicting rotation, the velocity is given by a vector cross product as
which is a vector perpendicular to both and , tangential to the orbit, and of magnitude . Likewise, the acceleration is given by
which is a vector perpendicular to both and of magnitude and directed exactly opposite to .
In the simplest case the speed, mass, and radius are constant.
Consider a body of one kilogram, moving in a circle of radius one metre, with an angular velocity of one radian per second.
The speed is 1 metre per second.
The inward acceleration is 1 metre per square second, .
It is subject to a centripetal force of 1 kilogram metre per square second, which is 1 newton.
The momentum of the body is 1 kg·m·s−1.
The moment of inertia is 1 kg·m2.
The angular momentum is 1 kg·m2·s−1.
The kinetic energy is 0.5 joule.
The circumference of the orbit is 2 (~6.283) metres.
The period of the motion is 2 seconds.
The frequency is (2)−1 hertz.
In polar coordinates
During circular motion, the body moves on a curve that can be described in the polar coordinate system as a fixed distance from the center of the orbit taken as the origin, oriented at an angle from some reference direction. See Figure 4. The displacement vector is the radial vector from the origin to the particle location:
where is the unit vector parallel to the radius vector at time and pointing away from the origin. It is convenient to introduce the unit vector orthogonal to as well, namely . It is customary to orient to point in the direction of travel along the orbit.
The velocity is the time derivative of the displacement: | Circular motion | Wikipedia | 466 | 574544 | https://en.wikipedia.org/wiki/Circular%20motion | Physical sciences | Classical mechanics | Physics |
Because the radius of the circle is constant, the radial component of the velocity is zero. The unit vector has a time-invariant magnitude of unity, so as time varies its tip always lies on a circle of unit radius, with an angle the same as the angle of . If the particle displacement rotates through an angle in time , so does , describing an arc on the unit circle of magnitude . See the unit circle at the left of Figure 4. Hence:
where the direction of the change must be perpendicular to (or, in other words, along ) because any change in the direction of would change the size of . The sign is positive because an increase in implies the object and have moved in the direction of .
Hence the velocity becomes:
The acceleration of the body can also be broken into radial and tangential components. The acceleration is the time derivative of the velocity:
The time derivative of is found the same way as for . Again, is a unit vector and its tip traces a unit circle with an angle that is . Hence, an increase in angle by implies traces an arc of magnitude , and as is orthogonal to , we have:
where a negative sign is necessary to keep orthogonal to . (Otherwise, the angle between and would decrease with an increase in .) See the unit circle at the left of Figure 4. Consequently, the acceleration is:
The centripetal acceleration is the radial component, which is directed radially inward:
while the tangential component changes the magnitude of the velocity:
Using complex numbers
Circular motion can be described using complex numbers. Let the axis be the real axis and the axis be the imaginary axis. The position of the body can then be given as , a complex "vector":
where is the imaginary unit, and is the argument of the complex number as a function of time, .
Since the radius is constant:
where a dot indicates differentiation in respect of time.
With this notation, the velocity becomes:
and the acceleration becomes:
The first term is opposite in direction to the displacement vector and the second is perpendicular to it, just like the earlier results shown before. | Circular motion | Wikipedia | 423 | 574544 | https://en.wikipedia.org/wiki/Circular%20motion | Physical sciences | Classical mechanics | Physics |
Velocity
Figure 1 illustrates velocity and acceleration vectors for uniform motion at four different points in the orbit. Because the velocity is tangent to the circular path, no two velocities point in the same direction. Although the object has a constant speed, its direction is always changing. This change in velocity is caused by an acceleration , whose magnitude is (like that of the velocity) held constant, but whose direction also is always changing. The acceleration points radially inwards (centripetally) and is perpendicular to the velocity. This acceleration is known as centripetal acceleration.
For a path of radius , when an angle is swept out, the distance traveled on the periphery of the orbit is . Therefore, the speed of travel around the orbit is
where the angular rate of rotation is . (By rearrangement, .) Thus, is a constant, and the velocity vector also rotates with constant magnitude , at the same angular rate .
Relativistic circular motion
In this case, the three-acceleration vector is perpendicular to the three-velocity vector,
and the square of proper acceleration, expressed as a scalar invariant, the same in all reference frames,
becomes the expression for circular motion,
or, taking the positive square root and using the three-acceleration, we arrive at the proper acceleration for circular motion:
Acceleration
The left-hand circle in Figure 2 is the orbit showing the velocity vectors at two adjacent times. On the right, these two velocities are moved so their tails coincide. Because speed is constant, the velocity vectors on the right sweep out a circle as time advances. For a swept angle the change in is a vector at right angles to and of magnitude , which in turn means that the magnitude of the acceleration is given by
Non-uniform circular motion
In non-uniform circular motion, an object moves in a circular path with varying speed. Since the speed is changing, there is tangential acceleration in addition to normal acceleration.
The net acceleration is directed towards the interior of the circle (but does not pass through its center).
The net acceleration may be resolved into two components: tangential acceleration and centripetal acceleration. Unlike tangential acceleration, centripetal acceleration is present in both uniform and non-uniform circular motion.
In non-uniform circular motion, the normal force does not always point to the opposite direction of weight. | Circular motion | Wikipedia | 478 | 574544 | https://en.wikipedia.org/wiki/Circular%20motion | Physical sciences | Classical mechanics | Physics |
The normal force is actually the sum of the radial and tangential forces. The component of weight force is responsible for the tangential force (when we neglect friction). The centripetal force is due to the change in the direction of velocity.
The normal force and weight may also point in the same direction. Both forces can point downwards, yet the object will remain in a circular path without falling down.
The normal force can point downwards. Considering that the object is a person sitting inside a plane moving in a circle, the two forces (weight and normal force) will point down only when the plane reaches the top of the circle. The reason for this is that the normal force is the sum of the tangential force and centripetal force. The tangential force is zero at the top (as no work is performed when the motion is perpendicular to the direction of force). Since weight is perpendicular to the direction of motion of the object at the top of the circle and the centripetal force points downwards, the normal force will point down as well.
From a logical standpoint, a person travelling in that plane will be upside down at the top of the circle. At that moment, the person's seat is actually pushing down on the person, which is the normal force.
The reason why an object does not fall down when subjected to only downward forces is a simple one. Once an object is thrown into the air, there is only the downward gravitational force that acts on the object. That does not mean that once an object is thrown into the air, it will fall instantly. The velocity of the object keeps it up in the air. The first of Newton's laws of motion states that an object's inertia keeps it in motion; since the object in the air has a velocity, it will tend to keep moving in that direction.
A varying angular speed for an object moving in a circular path can also be achieved if the rotating body does not have a homogeneous mass distribution.
One can deduce the formulae of speed, acceleration and jerk, assuming that all the variables to depend on :
Further transformations may involve and their corresponding derivatives: | Circular motion | Wikipedia | 440 | 574544 | https://en.wikipedia.org/wiki/Circular%20motion | Physical sciences | Classical mechanics | Physics |
Applications
Solving applications dealing with non-uniform circular motion involves force analysis. With a uniform circular motion, the only force acting upon an object traveling in a circle is the centripetal force. In a non-uniform circular motion, there are additional forces acting on the object due to a non-zero tangential acceleration. Although there are additional forces acting upon the object, the sum of all the forces acting on the object will have to be equal to the centripetal force.
Radial acceleration is used when calculating the total force. Tangential acceleration is not used in calculating total force because it is not responsible for keeping the object in a circular path. The only acceleration responsible for keeping an object moving in a circle is the radial acceleration. Since the sum of all forces is the centripetal force, drawing centripetal force into a free body diagram is not necessary and usually not recommended.
Using , we can draw free body diagrams to list all the forces acting on an object and then set it equal to . Afterward, we can solve for whatever is unknown (this can be mass, velocity, radius of curvature, coefficient of friction, normal force, etc.). For example, the visual above showing an object at the top of a semicircle would be expressed as .
In a uniform circular motion, the total acceleration of an object in a circular path is equal to the radial acceleration. Due to the presence of tangential acceleration in a non uniform circular motion, that does not hold true any more. To find the total acceleration of an object in a non uniform circular, find the vector sum of the tangential acceleration and the radial acceleration.
Radial acceleration is still equal to . Tangential acceleration is simply the derivative of the speed at any given point: . This root sum of squares of separate radial and tangential accelerations is only correct for circular motion; for general motion within a plane with polar coordinates , the Coriolis term should be added to , whereas radial acceleration then becomes . | Circular motion | Wikipedia | 403 | 574544 | https://en.wikipedia.org/wiki/Circular%20motion | Physical sciences | Classical mechanics | Physics |
Callinectes sapidus (from the Ancient Greek ,"beautiful" + , "swimmer", and Latin , "savory"), the blue crab, Atlantic blue crab, or, regionally, the Maryland blue crab, is a species of crab native to the waters of the western Atlantic Ocean and the Gulf of Mexico, and introduced internationally.
C. sapidus is of considerable culinary and economic importance in the United States, particularly in Louisiana, the Carolinas, the Chesapeake Bay, Delaware, and New Jersey. It is the Maryland state crustacean and the state's largest commercial fishery. Due to overfishing and environmental pressures some of the fisheries have seen declining yields, especially in the Chesapeake Bay fishery.
Unlike the other fisheries affected by climate change, blue crab is expected to do well; warming causes better breeding conditions, more survivable winters, and a greater range of habitable areas on the Atlantic coast. Whether this will have negative effects on the surrounding ecosystems from an increased crab population is still unclear.
Description
C. sapidus is a decapod crab of the swimming crab family Portunidae. The genus Callinectes is distinguished from other portunid crabs by the lack of an internal cartilaginous spine on the carpus (the middle segment of the claw), as well as by the T-shape of the male abdomen. Blue crabs may grow to a carapace width of . C. sapidus individuals exhibit sexual dimorphism. Males and females are easily distinguished by the shape of the abdomen (known as the "apron") and by color differences in the chelipeds, or claws. The abdomen is long and slender in males, but wide and rounded in mature females. A popular mnemonic is that the male's apron is shaped like the Washington Monument, while the mature female's resembles the dome of the United States Capitol. Claw color differences are more subtle than apron shape. The immovable, fixed finger of the claws in males is blue with red tips, while females have orange coloration with purple tips. A female's abdomen changes as it matures: an immature female has a triangular-shaped abdomen, whereas a mature female's is rounded. | Callinectes sapidus | Wikipedia | 458 | 574796 | https://en.wikipedia.org/wiki/Callinectes%20sapidus | Biology and health sciences | Crabs and hermit crabs | Animals |
Other species of Callinectes may be easily confused with C. sapidus because of overlapping ranges and similar morphology. One species is the lesser blue crab (C. similis). It is found further offshore than the common blue crab, and has a smoother granulated carapace. Males of the lesser blue crab also have mottled white coloration on the swimming legs, and females have areas of violet coloration on the internal surfaces of the claws. C. sapidus can be distinguished from another related species found within its range, C. ornatus, by number of frontal teeth on the carapace. C. sapidus has four, while C. ornatus has six.
The crab's blue hue stems from a number of pigments in the shell, including alpha-crustacyanin, which interacts with a red pigment, astaxanthin, to form a greenish-blue coloration. When the crab is cooked, the alpha-crustacyanin breaks down, leaving only the astaxanthin, which turns the crab to a bright orange-red color.
Organochlorides are found by Sheridan et al 1975 to be transferred to the C. sapidus hepatopancreas. They find that among organochlorides, DDT specifically is converted both to DDE and DDD in this crab.
Distribution
C. sapidus is native to the western edge of the Atlantic Ocean from Cape Cod to Argentina and around the entire coast of the Gulf of Mexico. It has recently been reported north of Cape Cod in the Gulf of Maine, potentially representing a range expansion due to climate change. It has been introduced (via ballast water) to Japanese and European waters, and has been observed in the Baltic, North, Mediterranean, and Black Seas. The first record from European waters was made in 1901 at Rochefort, France. In some parts of its introduced range, C. sapidus has become the subject of crab fishery, including in Greece, where the local population may be decreasing as a result of overfishing. In Italy, public awareness of the detrimental impact of this species on local molluscs is rapidly growing and, especially in the Po delta area and on the Adriatic Sea coast, eradication efforts are undergoing, both by local authorities and by local fishermen. | Callinectes sapidus | Wikipedia | 474 | 574796 | https://en.wikipedia.org/wiki/Callinectes%20sapidus | Biology and health sciences | Crabs and hermit crabs | Animals |
Ecology
The natural predators of C. sapidus include eels, drum, striped bass, spot, trout, some sharks, humans, cownose rays, and whiptail stingrays. C. sapidus is an omnivore, eating both plants and animals. It typically consumes thin-shelled bivalves (such as clams, mussels, and oysters), crustaceans, annelids, small fish, plants (such as eelgrass), and nearly any other item it can find, including carrion, other C. sapidus individuals, and animal waste. In salt marshes, C. sapidus will eat marsh periwinkles, Littoraria irrorata during high tides. Although an aquatic predator, C. sapidus will remain in shallow pits in salt marshes at low tide and ambush intertidal prey such as fiddler crabs (e.g., Minuca pugnax) and purple marsh crabs (Sesarma reticulatum) C. sapidus may be able to control populations of the invasive green crab, Carcinus maenas; numbers of the two species are negatively correlated, and C. maenas is not found in the Chesapeake Bay, where C. sapidus is most abundant.
C. sapidus is subject to a number of diseases and parasites. These include a number of viruses, bacteria, microsporidians, ciliates, and others. The nemertean worm Carcinonemertes carcinophila commonly parasitizes C. sapidus, especially females and older crabs, although it has little adverse effect on the crab. A trematode that parasitizes C. sapidus is itself targeted by the hyperparasite Urosporidium crescens. The most harmful parasites may be the microsporidian Ameson michaelis, the amoeba Paramoeba perniciosa and the dinoflagellate Hematodinium perezi, which causes "bitter crab disease".
In 2021, scientists from the University of Maryland completed DNA sequencing on C. sapidus's genome in Baltimore after six years of research to help better understand the species. This genetic map is expected to help scientists understand how the blue crabs will be affected by climate change and warmer water temperatures, along with which mutations cause disease, traits that influence meat production, and which females have the best reproductive ability.
Lifecycle | Callinectes sapidus | Wikipedia | 507 | 574796 | https://en.wikipedia.org/wiki/Callinectes%20sapidus | Biology and health sciences | Crabs and hermit crabs | Animals |
Growth
Eggs of C. sapidus hatch in high-salinity waters of inlets, coastal waters, and mouths of rivers, and are carried to the ocean by ebb tides. During seven planktonic (zoeal) stages, blue crab larvae float near the surface and feed on microorganisms they encounter. After the eighth zoeal stage, larvae molt into megalopae. This larval form has small claws called chelipeds for grasping prey items. Megalopae selectively migrate upward in the water column as tides travel landward toward estuaries. Eventually, blue crabs arrive in brackish water, where they spend the majority of their lives. Chemical cues in estuarine water prompt metamorphosis to the juvenile phase, after which blue crabs appear similar to the adult form. | Callinectes sapidus | Wikipedia | 168 | 574796 | https://en.wikipedia.org/wiki/Callinectes%20sapidus | Biology and health sciences | Crabs and hermit crabs | Animals |
A blue crab grows by shedding its exoskeleton, or molting, to expose a new, larger exoskeleton. After it hardens, the new shell fills with body tissue. Shell hardening occurs most quickly in low-salinity water where high osmotic pressure allows the shell to become rigid soon after molting. Molting reflects only incremental growth, making age estimation difficult. For blue crabs, the number of molts in a lifetime is fixed at about 25. Females typically exhibit 18 molts after the larval stages, while postlarval males molt about 20 times.
Male blue crabs tend to grow broader and have more accentuated lateral spines than females. Growth and molting are profoundly influenced by temperature and food availability. Higher temperatures and greater food resources decrease the period of time between molts, as well as the change in size during molts (molt increment). Salinity and disease also have subtle impacts on molting and growth rate. Molting occurs more rapidly in low-salinity environments. The high osmotic pressure gradient causes water to quickly diffuse into a soft, recently molted blue crab's shell, allowing it to harden more quickly. The effects of diseases and parasites on growth and molting are less well understood, but in many cases have been observed to reduce growth between molts. For example, mature female blue crabs infected with the parasitic rhizocephalan barnacle Loxothylacus texanus appear extremely stunted in growth when compared to uninfected mature females. Blue crabs may reach maturity within one year of hatching in the Gulf of Mexico, while Chesapeake Bay crabs may take up to 18 months to mature. As a result of different growth rates, commercial and recreational crabbing occur year-round in the Gulf of Mexico, while crabbing seasons are closed for colder parts of the year in northern states.
Reproduction | Callinectes sapidus | Wikipedia | 402 | 574796 | https://en.wikipedia.org/wiki/Callinectes%20sapidus | Biology and health sciences | Crabs and hermit crabs | Animals |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.