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sheep gave birth to a lamb. This lamb, “Dolly,” was the first successful clone generated from a differentiated animal cell. Wilmut’s successful cloning of fully differentiated sheep cells is a milestone event in gene technology. Even though his procedure proved inefficient (only one of 277 trials succeeded), it establ...
one of them is capable by itself of developing into a healthy individual. In cattle breeding, for example, these cells are frequently separated by the breeder and used to produce multiple clones of valuable offspring. The exciting promise of these embryonic stem cells is that, because they can develop into any tissue,...
The approach seems very straightforward, and should apply to humans. Indeed, blood stem cells are already routinely used in humans to replenish the bone marrow of cancer patients after marrow-destroying therapy. The problem Egg Inner cell mass Embryonic stem-cell culture Sperm Blastocyst Once sperm cell and egg cell h...
in the growing culture, islet cells that must have been produced from stem cells. Now on to juvenile diabetes. The scientists injected their cell culture into the pancreas of mice specially bred to develop juvenile diabetes. Unable to manufacture their own insulin because they had no islet cells, these diabetic mice c...
Might there not be a danger that some of the resulting bacteria would transmit an infective form of cancer? Could genetically engineered products administered to plants or animals turn out to be dangerous for consumers after several generations? What kind of unforeseen impact on the ecosystem might “improved” crops ha...
the second class of modification, where a gene is added to improve the nutritional character of some food, the food will be nutritionally different. In each of these instances, it is necessary to examine the possibility that consumers may prove allergic to the product of the introduced gene. In one instance, for examp...
beans in Europe, any more than genes can flow from you to other kinds of animals. CALVIN AND HOBBES ©1995 Watterson. Dist. by Universal Press Syndicate. Reprinted with permission. All rights reserved. On either score, then, the risk of bioengineering to the environment seems to be very slight. Indeed, in some cases it ...
fear remains, though, for the simple reason that no amount of information can remove it. Like a child scared of a monster under the bed, looking under the bed again doesn't help— the monster still might be there next time. And that means we are going to have to have GM labels, for people have every right to be informe...
• Genetic engineering experiments consist of four stages: isolation of DNA, production of recombinant DNA, cloning, and screening for the gene(s) of interest. • Preliminary screening can be accomplished by making the desired clones resistant to an antibiotic; hybridization can then be employed to identify the gene of ...
Secrets of Your Genes? Part VI Evolution Catching evolution in action A hundred years ago Charles Darwin’s theory of evolution by natural selection was taught as the foundation of biology in public schools throughout the United States. Then something happened. In the 1920s, conservative religious groups began to argue...
evolution of these differences can be experimentally tested. omy and history, relying on observation and deduction rather than experiment and induction to examine ideas about past events. Nonetheless, evolutionary biology is not entirely an observational science. Darwin was right about many things, but one area in whi...
, few predators prey on guppies. As a result, guppy populations above and below waterfalls have evolved many differences. In the high-predation pools, guppies exhibit drab coloration. Moreover, they tend to reproduce at a younger age. The differences suggest the action of natural selection. Perhaps as a result of shunt...
ppies: they matured late, attained greater size and brighter colors. Control populations in the lower pools, by contrast, continued to mature early and at smaller size. These results demonstrate that substantial evolutionary change can occur in less than 12 years. To explore this concept further go to our interactive l...
core of evolutionary biology. 421 20.1 Genes vary in natural populations. Gene Variation Is the Raw Material of Evolution Evolution Is Descent with Modification The word “evolution” is widely used in the natural and social sciences. It refers to how an entity—be it a social system, a gas, or a planet—changes through t...
ass the long-neck trait on to their offspring. (b) Darwin's theory: variation is inherited. FIGURE 20.2 How did giraffes evolve a long neck? in the genetic makeup of populations. Allele frequencies can also change as the result of repeated mutations from one allele to another and from migrants bringing alleles into a p...
organisms, except for those that reproduce asexually. In nature, genetic variation is the rule. Enzyme Polymorphism Many loci in a given population have more than one allele at frequencies significantly greater than would occur from mutation alone. Researchers refer to a locus with more variation than can be explained...
the progeny of a hybrid had not yet been discovered. Selection, scientists then thought, should always favor an optimal form, and so tend to eliminate variation. Moreover, the theory of blending inheritance—in which offspring were expected to be phenotypically intermediate relative to their parents—was widely accepted...
heterozygous with alleles B + b) (Individuals homozygous for allele b) If q2 = 0.16 (the frequency of white cats), then q = 0.4. Therefore, p, the frequency of allele B, would be 0.6 (1.0 – 0.4 = 0.6). We can now easily calculate the genotype frequencies: there are p2 = (0.6)2 100 (the number of cats in the total popu...
.36 (that is, 0.6 0.6), and approximately 36% of the individuals in the population will continue to have the BB genotype. The frequency of bb individuals is q2 (0.4 0.4) and so will continue to be about 16%, and the frequency of Bb individuals will be 2pq (2 0.6 0.4), or approximately 48%. Phenotypically, if the popula...
Genetic drift Statistical accidents. Usually occurs only in very small populations. Selection The only form that produces adaptive evolutionary changes. ment are important. In fact, they are the key to the importance of the Hardy–Weinberg principle, because individual allele frequencies often change in natural populat...
(d) Genetic drift 2. Gene Flow Gene flow is the movement of alleles from one population to another. It can be a powerful agent of change because members of two different populations may exchange genetic material. Sometimes gene flow is obvious, as when an animal moves from one place to another. If the characteristics ...
a higher proportion of heterozygous individuals. By increasing homozygosity in a population, inbreeding increases the expression of recessive alleles. It is for this reason that marriage between close relatives is discouraged and to some degree outlawed—it increases the possibility of producing children homozygous for...
you were to replicate this experiment 1000 times, each time randomly drawing four individuals from the parental population, one of the two alleles would be missing entirely from about 8 of the 1000 populations. This leads to an important conclusion: genetic drift leads to the loss of alleles in isolated populations. T...
no more than 20 individuals on the island of Guadalupe off the coast of Baja, California. As a result of this bottleneck, even though the seal populations have rebounded and now number in the tens of thousands, this species has lost almost all of its genetic variation. Chapter 20 Genes within Populations 427 5. Select...
variation is genetically based will natural selection lead to evolution. 428 Part VI Evolution Selection to Avoid Predators. Many of the most dramatic documented instances of adaptation involve genetic changes which decrease the probability of capture by a predator. The caterpillar larvae of the common sulphur butterf...
the enzyme that is more frequent in the north is a better catalyst at low temperatures than the enzyme from the south. Moreover, functional studies indicate that at low temperatures, individuals with the northern allele swim faster, and presumably survive better, than individuals with the alternative allele. Selection...
target sites for the pesticide FIGURE 20.9 Selection for pesticide resistance. Resistance alleles at genes like pen and kdr allow insects to be more resistant to pesticides. Insects that possess these resistance alleles have become more common through selection. Chapter 20 Genes within Populations 429 Identifying the ...
to measure with precision. As a result, the theory can account for almost any value of H¯¯, making it very difficult to prove or disprove. As you might expect, a great deal of controversy has resulted. 430 Part VI Evolution Testing the Neutral Theory Choosing between the adaptive selection theory and the neutral theor...
with the relative contribution varying from one gene to the next. Adaptive selection clearly maintains some enzyme polymorphisms in natural populations. Genetic drift seems to play a major role in producing the variation we see at the DNA level. For most enzyme-level polymorphism, investigators cannot yet choose betwe...
gene flow were going on between the two populations, then the less favored allele would continually be reintroduced into each population. As a result, the frequency of the two alleles in each population would reflect a balance between the rate at which gene flow brings the inferior allele into a population versus the ...
to maintain variation in the population. The reason is simple. Instead of tending to remove less successful alleles from a population, such heterozygote advantage will favor individuals with copies of both alleles, and thus will work to maintain both alleles in the population. Some evolutionary biologists believe that...
ozygous or homozygous for the valine-specifying allele (designated allele S) are said to possess the sickle cell trait. Heterozygotes produce some sickle-shaped red blood cells, but only 2% of the number seen in homozygous individuals. The reason is that in heterozygotes, one-half of the molecules do not contain valine...
, and 1 in 100 develops the fatal form of the disorder. People who are homozygous for the sickle cell allele almost never reproduce because they usually die before they reach reproductive age. Why is the S allele not eliminated from the Central African population by selection, rather than being maintained at such high ...
figure 13.18). In such cases, selection operates on all the genes, influencing most strongly those that make the greatest contribution to the phenotype. How selection changes the population depends on which genotypes are favored. Disruptive Selection In some situations, selection acts to eliminate rather than to favor...
fly toward light 0 2 4 8 6 10 Number of generations 12 14 16 18 20 2 3 4 5 6 7 8 9 10 Birth weight in pounds 100 70 50 30 20 10 7 5 3 2 FIGURE 20.14 Directional selection for phototropism in Drosophila. In generation after generation, individuals of the fly Drosophila were selectively bred to obtain two populations. W...
Evolutionary biologists quantify reproductive success as fitness, the number of surviving offspring left in the next generation. Although selection is often characterized as “survival of the fittest,” differences in survival are only one component of fitness. Even if no differences in survival occur, selection may ope...
contains more ommatidia than the right eye. However, despite intense selection in the laboratory, scientists have never been able to produce a line of fruit flies that consistently have more ommatidia in the left eye than in the right. The reason is that separate genes do not exist for the left and right eyes. Rather,...
0.6 0.8 1.0 Frequency of a FIGURE 20.18 The relationship between allele frequency and genotype frequency. If allele a is present at a frequency of 0.2, the double recessive genotype aa is only present at a frequency of 0.04. In other words, only 4 in 100 individuals will have a homozygous recessive genotype, while 64 ...
of a suitable explanation of how hereditary traits are transmitted. • Invertebrates and outcrossing plants are often heterozygous at about 12 to 15% of their loci; the corresponding value for vertebrates is about 4 to 8%. 20.2 Why do allele frequencies change in populations? • Studies of how allele frequencies shift w...
Evolutionary Variation • Other Processes of Evolution • Adaptation 7. Define selection. How does it alter allele frequencies? What are the three types of selection? Give an example of each. 8. Why are there limitations to the success of selection? • Book Review: The Evolution of Jane by Schine 21 The Evidence for Evol...
This is not because the average person truly understands the basic facts of evolution, but rather because many people mistakenly believe that it represents a challenge to their religious beliefs. Similar highly publicized criticisms of evolution have occurred ever since Darwin’s time. For this reason, it is important ...
otopes contained in the rock (absolute dating); the older the rock, the more its isotopes have decayed. Because radioactive isotopes decay at a constant rate unaltered by temperature or pressure, the isotopes in a rock act as an internal clock, measuring the time since the rock was formed. This is a more accurate way o...
being seen in the fossil record over a period of 12 million years (figure 21.4). A host of other examples all illustrate a record of successive change. The demonstration of this successive change is one of the strongest lines of evidence that evolution has occurred. The fossil record provides a clear record of the maj...
’t look much like horses at all. Small, with short legs and broad feet (figure 21.5), these species occurred in wooded habitats, where they probably browsed on leaves and herbs and escaped predators by dodging through openings in the forest vegetation. The evolutionary path from these diminutive creatures to the workho...
25 20 15 10 5 0 Millions of years ago FIGURE 21.6 Evolutionary change in body size of horses. Lines show the broad outline of evolutionary relationships. Although most change involved increases in size, some decreases also occurred. teeth down. Accompanying these changes have been alterations in the shape of the skull...
day Equus. However, today’s limited horse diversity—only one surviving genus—is unusual. Indeed, at the peak of horse diversity in the Miocene, as many as 13 genera of horses could be found in North America alone. These species differed in body size and in a wide variety of other characteristics. Presumably, they lived...
, another a cactus eater, yet another a “vampire” that creeps up on seabirds and uses its sharp beak to drink their blood. Perhaps most remarkable are the tool users, woodpecker finches that pick up a twig, cactus thorn, or leaf stalk, trim it into shape with their bills, and then poke it into dead branches to pry out ...
species are able to get enough to eat. Later work has revealed a very different picture during leaner, dry years, when few seeds are available and the difference between survival and starvation depends on being able to efficiently gather enough to eat. In such times, having beaks designed to be maximally effective for...
frequencies, but rather are simply a response to diet— perhaps during lean times the birds become malnourished and then grow stouter beaks, for example. To rule out this possibility, the Grants measured the relation of parent bill size to offspring bill size, examining many broods over several years. The depth of the ...
on tree trunks, making the trunks darker. Selection for Melanism Can Darwin’s theory explain the increase in the frequency of the dark allele? Why did dark moths gain a survival advantage around 1850? An amateur moth collector named J. W. Tutt proposed what became the most commonly accepted hypothesis explaining the d...
the evolutionary process in which darker individuals come to predominate over lighter individuals since the industrial revolution as a result of natural selection. The process is widely believed to have taken place because the dark organisms are better concealed from their predators in habitats that have been darkened...
15 were melanic, a frequency of 89%. The American Clean Air Act, passed in 1963, led to significant reductions in air pollution. Resampled in 1994, the Detroit field station peppered moth population had only 15% melanic moths (see figure 21.11)! The moths in Liverpool and Detroit, both part of the same natural experime...
every case in which it has been applied. This success is strong proof that selection is an effective evolutionary process. Laboratory Experiments With the rise of genetics as a field of science in the 1920s and 1930s, researchers began conducting experiments to test the hypothesis that selection can produce evolutiona...
(figure 21.13). These differences have resulted from generations of selection for desirable traits like milk production and corn stalk size. An experimental study with corn demonstrates the ability of artificial selection to rapidly produce major change in crop plants. In 1896, agricultural scientists began selecting ...
Major Evolutionary Changes? Given that we can observe the results of selection operating over relatively short periods of time, most scientists believe that natural selection is the process responsible for the evolutionary changes documented in the fossil record. Some critics of evolution accept that selection can lea...
their evolutionary past. For example, the forelimbs of vertebrates are all homologous structures, that is, structures with different appearances and functions that all derived from the same body part in a common ancestor. You can see in figure 21.15 how the bones of the forelimb have been modified in different ways fo...
muscles for wiggling their ears, just as a coyote does (table 21.1). Boa constrictors have hip bones and rudimentary hind legs. Manatees (a type of aquatic mammal often referred to as “sea cows”) have fingernails on their fins (which evolved from legs). Figure 21.17 illustrates the skeleton of a baleen whale, which co...
; most adults only have three to five tiny tail bones and, occasionally, a trace of a tail-extending muscle. Structure which presumably had a digestive function in some of our ancestors, like the cecum of some herbivores. In humans, it varies in length from 5–15 cm, and some people are born without one. Molars that are...
are also evident when the DNA itself is compared. For example, chimps and humans, which are thought to have descended from a common ancestor that lived approximately 6 million years ago, exhibit few differences in their DNA. 452 Part VI Evolution Human Macaque Dog Bird Frog Lamprey 8 e m T i 32 45 67 10 20 30 40 50 60...
these instances has tended to favor changes that made the two groups more alike, their phenotypes have converged. This form of evolutionary change is referred to as convergent evolution, or sometimes, parallel evolution. The Marsupial-Placental Convergence Burrower Anteater Mouse Climber Glider Cat Wolf In the best-kn...
introduced by settlers, for example, have drastically altered the vegetation. Darwin and Patterns of Recent Divergence Darwin was the first to present evidence that animals and plants living on oceanic islands resemble most closely the forms on the nearest continent—a relationship that only makes sense as reflecting c...
for macroevolution is overwhelming. In the next chapter, we will consider Darwin’s proposal that microevolutionary changes have led directly to macroevolutionary changes, the key argument in his theory that evolution occurs by natural selection. Evolution favors similar forms under similar circumstances. Convergence i...
events, not more organized.” Biologists point out that this argument ignores what the second law really says: disorder increases in a closed system, which the earth most certainly is not. Energy continually enters the biosphere from the sun, fueling life and all the processes that organize it. 5. Proteins are too impr...
system evolved at the dawn of the vertebrates 600 million years ago, and is found today in lampreys, the most primitive fish. One hundred million years later, as vertebrates evolved, proteins were added to the clotting system making it sensitive to substances released from damaged tissues. Fifty million years later, a...
4. Why did the frequency of light-colored moths decrease and that of dark-colored moths increase with the advent of industrialism? What is industrial melanism? 5. What can artificial selection tell us about evolution? Is artificial selection a good analogy for the selection that occurs in nature? 21.3 Evidence for evo...
isolation generally occurs more quickly when populations are adapting to different environments. The Geography of Speciation. Speciation occurs most readily when populations are geographically isolated. Sympatric speciation can occur by polyploidy and, perhaps, by other means. 22.4 Clusters of species reflect rapid ev...
feeder on your balcony or back porch and you will attract a wide variety of different types of birds (especially if you put out a variety of different kinds of foods). In the midwestern United States, for example, you might routinely see cardinals, blue jays, downy woodpeckers, house finches—even hummingbirds in the su...
triangulum syspila) Eastern milk snake (Lampropeltis triangulum triangulum) “Intergrade” form Scarlet kingsnake (Lampropeltis triangulum elapsoides) FIGURE 22.3 Geographic variation in the milk snake, Lampropeltis triangulum. Although each subspecies appears phenotypically quite distinctive from the others, they are c...
name, the concept is really a zoological species concept and applies less readily to plants. Even among animals, the biological species concept appears to apply more successfully to some groups than to others. As we will see in section 22.4, biologists are currently reevaluating this and other approaches to the study ...
The valley oak, a graceful deciduous tree that can be as tall as 35 meters, occurs in the fertile soils of open grassland on gentle slopes and valley floors. In contrast, the scrub oak is an evergreen shrub, usually only 1 to 3 meters tall, which often forms the kind of dense scrub known as chaparral. The scrub oak is...
despite the great differences between them, D. heteroneura and D. silvestris are very closely related. Hybrids between them are fully fertile. The two species occur together over a wide area on the island of Hawaii, yet hybridization has been observed at only one locality. The very different and complex behavioral cha...
species may not attract one another. Many land animals may not hybridize successfully because the sperm of one species may function so poorly within the reproductive tract of another that fertilization never takes place. In plants, the growth of pollen tubes may be impeded in hybrids between different species. In both...
cannot become established in nature. (1) (2) (3) (4) FIGURE 22.6 Postzygotic isolation in leopard frogs. Numbers indicate the following species in the geographical ranges shown: (1) Rana pipiens; (2) Rana blairi; (3) Rana utricularia; (4) Rana berlandieri. These four species resemble one another closely in their exter...
The Origin of Species 463 Selection May Reinforce Isolating Mechanisms The formation of species is a continuous process, one that we can understand because of the existence of intermediate stages at all levels of differentiation. If populations that are partly differentiated come into contact with one another, they ma...
all may lead to changes in traits that cause reproductive isolation. For example, in the Hawaiian Islands, closely related species of Drosophila often differ greatly in their courtship behavior. Colonization of new islands by these fruit flies probably involves a founder effect, in which one or a few fruit flies—perha...
use their dewlaps in both territorial and courtship displays. Coexisting species almost always differ in their dewlaps, which are used in species recognition. Some dewlaps are easier to see in open habitats, whereas others are more visible in shaded environments. tions in different laboratory chambers and measure how ...
were strong enough, these two phenotypes would evolve into different species. However, before the two phenotypes could become different species, they would have to evolve reproductive isolating mechanisms. Because the two phenotypes would initially not be reproductively isolated at all, genetic exchange between indivi...
involve very few genes. Studying two species of monkeyflower found in the western United States, researchers found that only a few genes separate the two species, even though at first glance the two species appear to be very different (figure 22.10). Using gene technologies like those described in chapter 19, the rese...
Darwin’s Finches One of the most visible manifestations of evolution is the existence of groups of closely related species that have recently evolved from a common ancestor by occupying different habitats. This type of adaptive radiation occurred among the 13 species of Darwin’s finches on the Galápagos Islands. Presu...
(C. parvulus) Large insectivorous tree finch (C. psittacula) Vegetarian tree finch (Platyspiza crassirostris) W a r b l er bills Cactus eater Insect eaters G ro u n d fi Seed eaters bills finches ping e Tre s ra Bud eater Sharp-beaked ground finch (G. difficilis) Small ground finch (G. fuliginosa) Medium ground finch ...
are closely associated with the remarkable native plants of the islands and are often abundant in the native vegetation. Evidently, when their ancestors first reached these islands, they encountered many “empty” habitats that other kinds of insects and other animals occupied elsewhere. The evolutionary opportunities t...
down 14,000 years ago, isolating local populations in small lakes until the water level rose again. Cichlid Diversity These small, perchlike fishes range from 2 to 10 inches in length, and the males come in endless varieties of colors. The most diverse assembly of vertebrates known to science, the Lake Victoria cichli...
VI Evolution New Zealand Alpine Buttercups Adaptive radiations as we have described in Galápagos finches, Hawaiian Drosophila, and cichlid fishes seem to be favored by periodic isolation. Finches and Drosophila invade new islands, local species evolve, and they in turn reinvade the home island, in a cycle of expanding...
into one continuous range. Glaciers recede Mountain populations become isolated, permitting divergence and speciation. Glaciation Alpine zones are reconnected. Separately evolved species come back into contact. FIGURE 22.15 Periodic glaciation encouraged species formation among alpine buttercups in New Zealand. The fo...
ischus, (17) Hallucigenia. 472 Part VI Evolution 800 600 400 200 0 600 500 400 300 200 100 0 Cambrian (570-505) Ordovician (505-438) Silurian (438-408) Devonian (408-360) Carboniferous (360-280) Permian (280-248) Triassic (248-213) Jurassic (213-144) Cretaceous (144-65) Tertiary (65-2) Millions of years ago FIGURE 22.1...
inction The number of species in the world in recent times is greater than it has ever been. Unfortunately, that number is decreasing at an alarming rate due to human activities. Some estimate that as many as one-fourth of all species will become extinct in the next 50 years, a rate of extinction not seen on earth sinc...
areas. Such populations would be small, isolated, and possibly already differing from their parental population as a result of the founder effect. This, combined with selective pressures 474 Part VI Evolution e m T i (b) Gradualism (a) Punctuated equilibrium FIGURE 22.18 Two views of the pace of macroevolution. (a) Pu...
fossil record indicates that balsam poplars and cottonwoods have been phenotypically distinct for 12 million years, but throughout this time, they have routinely produced hybrids. Consequently, for many years, many botanists have felt that the biological species concept only applies to animals. What is becoming increa...
more successful for certain types of organisms or habitats. A variety of other ideas have been put forward to establish criteria for defining species. Many of these are specific to a particular type of organism and none has universal applicability. In truth, it may be that there is no single explanation for what maint...
s 5. How does selection relate to population divergence? 6. How many genes are involved in the speciation process? 7. When are hybrids at a disadvantage? What can be the result of this disadvantage? 8. Define the term polyploidy. • Reproductive isolation can arise as populations differentiate by adaptation to different...
evolved in Africa. African Origin: Early Homo. There may have been several species of early Homo, with brains significantly larger than those of australopithecines. Out of Africa: Homo erectus. The first hominid species to leave Africa was the relatively large-brained H. erectus, the longest lived species of Homo. 23....
, insect-eating environment: 1. Grasping fingers and toes. Unlike the clawed feet of tree shrews and squirrels, primates have grasping hands and feet that let them grip limbs, hang from branches, seize food, and, in some primates, use tools. The first digit in many primates is opposable and at least some, if not all, o...
improved senses, with the braincase forming a larger portion of the head. Anthropoids, like the relatively few diurnal prosimians, live in groups with complex social interactions. In addition, the anthropoids tend to care for their young for prolonged periods, allowing for a long childhood of learning and brain develo...
angutan (Pongo), gorilla (Gorilla), and chimpanzee (Pan) (figure 23.5). Apes have larger brains than monkeys, and they lack tails. With the exception of the gibbon, which is small, all living apes are larger than any monkey. Apes exhibit the most adaptable behavior of any mammal except human beings. Once widespread in ...
directly below the body, to carry its weight. Which Ape Is Our Closest Relative? Comparing Apes to Hominids Studies of ape DNA have explained a great deal about how the living apes evolved. The Asian apes evolved first. The line of apes leading to gibbons diverged from other apes about 15 million years ago, while oran...
of the body’s weight on the lower limbs, which comprise 32 to 38% of the body’s weight and are longer than the upper limbs; human upper limbs do not bear the body’s weight and make up only 7 to 9% of human body weight. African apes walk on all fours, with the upper and lower limbs both bearing the body’s weight; in go...
that the creature had walked upright. Dart concluded it was a human ancestor. What riveted Dart’s attention was that the rock in which the skull was embedded had been collected near other fossils that suggested that the rocks and their fossils were several million years old! At that time, the oldest reported fossils o...
skeleton was 40% complete and over 3 million years old. The skeleton and other similar fossils have been assigned the scientific name Australopithecus afarensis (from the Afar Desert). The shape of the pelvis indicated that Lucy was a female, and her leg bones proved she walked upright. Her teeth were distinctly homin...
al. Another school sees bipedalism as a precursor to bigger brains. Those who favor the brain-first hypothesis speculate that human intelligence was necessary to make the decision to walk upright and move out of the forests and onto the grassland. Those who favor the bipedalism-first hypothesis argue that bipedalism fr...
, for example, is situated far forward, as in other bipedal hominids. Some 4.4 million years old, it is the most ancient hominid yet discovered. It is significantly more apelike than any australopithecine and so has been assigned to a new genus, Ardipithecus from the local Afar language ardi for “ground” and the Greek ...

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