Learning Objectives

By the end of this section, friend will have completed the complying with objectives:

Describe the acquired features that differentiate primates from other animalsExplain why scientists are having difficulty determining the true present of lower in hominids

Order Primates of course Mammalia has lemurs, tarsiers, monkeys, apes, and also humans. Non-human primates live primarily in the tropic or subtropical areas of south America, Africa, and Asia. They selection in dimension from the mouse lemur at 30 grams (1 ounce) to the mountain gorilla in ~ 200 kilograms (441 pounds). The characteristics and evolution the primates is of particular interest to us as it enables us to understand the advancement of our very own species.

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Characteristics of Primates

All primate species possess adaptations because that climbing trees, together they every descended indigenous tree-dwellers. This arboreal heritage of primates has actually resulted in hands and also feet that are adapted for brachiation, or climbing and swinging with trees. This adaptations include, yet are not restricted to: 1) a rotating shoulder joint, 2) a large toe that is extensively separated from the various other toes and thumbs, which space widely be separate from finger (except humans), which allow for gripping branches, 3) stereoscopic vision, 2 overlapping fields of vision indigenous the eyes, which enables for the perception of depth and also gauging distance. Other attributes of primates room brains the are bigger than those of most other mammals, claws that have actually been modified into flattened nails, frequently only one offspring every pregnancy, and a trend towards holding the body upright.

Order Primates is divided into 2 groups: prosimians and also anthropoids. Prosimians include the bush babies of Africa, the lemurs that Madagascar, and also the lorises, pottos, and tarsiers of south-east Asia. Anthropoids encompass monkeys, apes, and humans. In general, prosimians tend to it is in nocturnal (in comparison to diurnal anthropoids) and also exhibit a smaller size and also smaller brain than anthropoids.

Evolution of Primates

The an initial primate-like mammals are described as proto-primates. They to be roughly comparable to squirrels and also tree shrews in size and appearance. The currently fossil proof (mostly from north Africa) is really fragmented. This proto-primates remain largely mysterious creatures until more fossil proof becomes available. The oldest known primate-like mammals with a reasonably robust fossil record is Plesiadapis (although part researchers do not agree the Plesiadapis was a proto-primate). Fossils of this primate have actually been date to around 55 million years ago. Plesiadapiforms to be proto-primates that had some features of the teeth and skeleton in typical with true primates. Castle were found in phibìc America and Europe in the Cenozoic and also went extinct by the finish of the Eocene.

The an initial true primates were uncovered in north America, Europe, Asia, and Africa in the Eocene Epoch. These early on primates resembled present-day prosimians such together lemurs. Evolutionary alters continued in these at an early stage primates, with bigger brains and eyes, and also smaller muzzles being the trend. By the finish of the Eocene Epoch, countless of the early on prosimian varieties went extinction due either to cooler temperatures or competition native the an initial monkeys.


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Figure 2. The (a) chimpanzee is among the good apes. It possesses a fairly large mind and has actually no tail. (b) All an excellent apes have a similar skeletal structure. (credit a: alteration of work by Aaron Logan; credit b: change of work by Tim Vickers)


Human Evolution

The family Hominidae of bespeak Primates includes the hominoids: the good apes (Figure 3). Evidence from the fossil record and also from a comparison of human and also chimpanzee DNA says that humans and also chimpanzees diverged from a typical hominoid ancestor about 6 million years ago. Several species evolved from the evolution branch that consists of humans, return our types is the only surviving member. The hatchet hominin is used to refer to those varieties that evolved after this split of the primate line, in order to designating types that are an ext closely associated to human beings than to chimpanzees. Hominins were predominantly bipedal and include those teams that likely gave rise to our species—including Australopithecus, Homo habilis, and also Homo erectus—and those non-ancestral groups that deserve to be considered “cousins” of contemporary humans, such together Neanderthals. Identify the true lines of lower in hominins is difficult. In year past, when relatively few hominin fossils had been recovered, some scientists believed that considering castle in order, from earliest to youngest, would show the food of evolution from early on hominins to modern-day humans. In the past several years, however, many new fossils have actually been found, and it is clear the there was often an ext than one species alive at any type of one time and also that plenty of of the fossils found (and varieties named) stand for hominin types that died out and are not ancestral to modern-day humans.


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Figure 4. The skull of (a) Australopithecus afarensis, very early hominid that lived between two and also three million years ago, resembled the of (b) contemporary humans however was smaller sized with a sloped forehead and also prominent jaw.


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Figure 6. Homo erectus had actually a prominent brow and a sleep that sharp downward quite than forward.


H. erectus appeared approximately 1.8 million years ago (Figure 6). The is believed to have originated in eastern Africa and also was the very first hominin species to migrate out the Africa. Fossils the H. erectus have been uncovered in India, China, Java, and Europe, and also were recognized in the previous as “Java Man” or “Peking Man.” H. erectus had a variety of features the were much more similar to modern humans than those ofH. habilis. H. erectus was larger in size than previously hominins, reaching heights approximately 1.85 meters and weighing approximately 65 kilograms, which room sizes similar to those of contemporary humans. Its level of sex-related dimorphism was less than previously species, through males being 20 come 30 percent larger than females, i beg your pardon is close come the size distinction seen in our species. H. erectus had a larger mind than earlier species at 775–1,100 cubic centimeters, i m sorry compares to the 1,130–1,260 cubic centimeters seen in modern human brains. H.erectus also had a nose with downward-facing nostrils similar to modern humans, fairly than the forward encountering nostrils uncovered in other primates. Longer, downward-facing nostrils enable for the warming the cold air prior to it beginning the lungs and also may have actually been one adaptation to chillier climates. Artifacts found through fossils that H. erectus suggest the it was the very first hominin to use fire, hunt, and have a home base. H. erectus is typically thought to have actually lived until about 50,000 years ago.

Humans: Homo sapiens


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Figure 7. The Homo neanderthalensis used tools and also may have worn clothing.


A number of species, periodically called archaic Homo sapiens, apparently developed from H. erectus starting about 500,000 year ago. These species include Homo heidelbergensis, Homo rhodesiensis, and also Homo neanderthalensis. These archaic H. sapiens had a mind size similar to the of contemporary humans, averaging 1,200–1,400 cubic centimeters. They differed from modern humans by having actually a thick skull, a prominent brow ridge, and a receding chin. Several of these species survived until 30,000–10,000 years ago, overlapping with modern-day humans (Figure 7).

There is substantial debate around the origins of anatomically modern humans or Homo sapiens sapiens. As disputed earlier, H.erectus moved out that Africa and into Asia and also Europe in the first major tide of migration around 1.5 million years ago. It is thought that contemporary humans emerged in Africa from H. erectus and migrated out the Africa about 100,000 years ago in a second significant migration wave. Then, modern humans replaced H. erectus species that had actually migrated right into Asia and also Europe in the an initial wave.

This evolutionary timeline is supported by molecule evidence. One strategy to examining the beginnings of contemporary humans is to examine mitochondrial DNA (mtDNA) native populations about the world. Since a fetus develops from one egg containing its mom mitochondria (which have their own, non-nuclear DNA), mtDNA is passed entirely through the maternal line. Mutations in mtDNA have the right to now be offered to estimate the timeline of hereditary divergence. The result evidence argues that all modern-day humans have actually mtDNA inherited indigenous a common ancestor that lived in Africa around 160,000 years ago. An additional approach come the molecular expertise of human advancement is to study the Y chromosome, i m sorry is passed from dad to son. This evidence argues that all guys today inherited a Y chromosome indigenous a male that stayed in Africa around 140,000 years ago.

Section Summary

All primate types possess adaptations because that climbing trees, as they all probably descended indigenous tree-dwellers, although no all species are arboreal. Other features of primates room brains that are bigger than those of other mammals, claws that have been modified into flattened nails, typically only one young per pregnancy, stereoscopic vision, and also a trend towards holding the body upright. Primates are separated into 2 groups: prosimians and also anthropoids. Monkeys evolved from prosimians during the Oligocene Epoch. Apes progressed from catarrhines in Africa during the Miocene Epoch. Apes are separated into the lesser apes and also the higher apes. Hominins include those teams that offered rise to our species, such together Australopithecus and also H. erectus, and those groups that have the right to be thought about “cousins” of humans, such together Neanderthals. Fossil evidence shows that hominins at the time of Australopithecus were walking upright, the an initial evidence of bipedal hominins. A number of species, periodically called antiquated H. sapiens, evolved from H.

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erectus about 500,000 year ago. Over there is significant debate about the beginnings of anatomically modern-day humans or Hsapiens sapiens.