Chapter 19 Primate and Human Evolution Oldest Hominid

Chapter 19 Primate and Human Evolution Oldest Hominid

Chapter 19 Primate and Human Evolution Oldest Hominid Sahelanthropus tchadensis, the oldest known hominid, nearly 7 million years old,

was discovered in 2002 in Chad Who are we? Who are we? Where did we come from?

What is the human genealogy? These are basic questions that probably everyone at some time or another has asked themselves Goes Back Farther Than We Thought Many people enjoy tracing their own family history as far back as they can, similarly paleoanthropologists are discovering, based on recent fossil finds that the human family tree goes back

much farther than we thought Hope of Life In fact, a skull found in the African nation of Chad, in 2002 and named Sahelanthropus tchadensis but nicknamed Tourma, which means "hope of life" in the local Goran language, has pushed back the origins of humans to nearly 7 million years ago

Instead of simplifying our ancestry, however, its discovery has raised more questions than it answered Bushy Model of Human Evolution For instance, paleoanthropologists now think that human evolution branched many times rather than evolving in a somewhat straight line leading to modern humans According to this bushy model

of human evolution, such key traits as upright walking, manual dexterity and a large brain evolved more than once, and produced many evolutionary dead-ends When Humans and Chimpanzees Diverged Presently, most paleoanthropologists accept

that the human-chimpanzee stock separated from gorillas about 8 million years ago and humans separated from chimpanzees about 5 million years ago Thus Sahelanthropus tchadensis is at or near the point in time when humans and chimpanzees diverged Oldest Hominid Besides being the oldest hominid, humans and their extinct ancestors,

Sahelanthropus tchadensis shows a mosaic of primitive and advanced features that has excited and puzzled paleoanthropologists The small brain case and most of the teeth (except the canines) are chimplike However, the nose, which is fairly flat, and the prominent brow ridges are features only seen, until now, in the human genus Homo

Understanding in Flux So where does this leave us, evolutionarily speaking? At a very exciting time as we seek to unravel the history of our species Our understanding of our genealogy is presently in flux, and each new fossil hominid find sheds more light on our ancestry

Human Evolution Apparently human evolution is just like that of other groups Just as with nonhominid predecessors,

our ancestors followed an uncertain path As new species evolved, they filled ecologic niches and either gave rise to descendants better adapted to the changing environment or became extinct New Hypotheses About Our Ancestry In this section we examine the various primate groups, in particular the origin and evolution of the

hominids, the group that includes our ancestors However, we must point out that new discoveries of fossil hominids, as well as new techniques for scientific analysis are leading to new hypotheses about our ancestry Continuing Discoveries Change Our Ideas As recently as 2000, the earliest fossil evidence of hominids

was from 4.4-million-year-old rocks in eastern Africa Since then, as just noted, discoveries have pushed that age back to almost 7 million years Exciting Study Even as we speak, therefore, new discoveries may have changed some of our conclusions based on what we currently know

Such is the nature of paleoanthropology and one reason why the study of hominids is so exciting What Are Primates? Primates are difficult to characterize as an order because they lack the strong specializations found in most other mammalian orders We can, however, point to several trends in their evolution that help define primates

and are related to their arboreal, or tree-dwelling, ancestry Trends in Primates These include changes in the skeleton

and mode of locomotion, an increase in brain size, a shift toward smaller, fewer, and less specialized teeth, and the evolution of stereoscopic vision and a grasping hand with opposable thumb Not all these trends took place in every primate group, nor did they evolve at the same rate in each group Variations

In fact, some primates have retained certain primitive features, whereas others show all or most of these trends Classification of Primates The primate order is divided into two suborders The prosimians, or lower primates, include the lemurs, lorises, tarsiers, and tree shrews, while the anthropoids, or higher primates, include monkeys, apes, and humans

Classification of Primates Order Primates: Suborder Prosimii: (lower primates) Lemurs, lorises, tarsiers, tree shrews Suborder Anthropoidea: (Higher primates) Monkeys, apes, humans Superfamily Cercopithecoidea: Macaque, baboon, proboscis monkey Superfamily Ceboidea: Howler, spider, and squirrel monkeys Superfamily Hominoidea: Apes, humans

Family Pongidae: Chimpanzees, orangutans, gorillas Family Hylobatidae: Gibbons, siamangs Family Hominidae: Humans Prosimians Prosimians are generally small, ranging from species the size of a mouse up to those as large as a house cat They are arboreal, have five digits on each hand and foot with either claws or nails,

and are typically omnivorous They have large, forwardly directed eyes specialized for night vision, hence most are nocturnal Tarsier Tarsiers are prosimian primates

Ring-Tailed Lemur Ring-Tailed Lemur are also prosimians Prosimians As their name implies pro means "before," and simian means "ape, prosimians are the oldest primate lineage,

and their fossil record extends back to the Paleocene During the Eocene prosimians were abundant, diversified, and widespread in North America, Europe, and Asia Eocene Prosimian Notharctus, a primitive Eocene prosimian from North America

Prosimians Declined in Cooler Climate As the continents moved northward during the Cenozoic and the climate changed from warm tropical

to cooler midlatitude conditions, the prosimian population decreased in both abundance and diversity Prosimians Are Tropical By the Oligocene, hardly any prosimians were left in the northern continents as the once widespread Eocene populations migrated south to the warmer latitudes of Africa, Asia, and Southeast Asia Presently, prosimians are found

only in the tropical regions of Asia, India, Africa, and Madagascar Anthropoids Anthropoids evolved from a prosimian lineage sometime during the Late Eocene, and by the Oligocene they were well established Anthropoids are divided into three superfamilies: New World Monkey

New World Monkeys constitute a superfamily belonging to the suborder Anthropoidea (anthropoids) Old Word Monkey Another superfamily of the anthropoids: the Old World

monkeys Great Apes The third superfamily is the great apes, which include Gorillas and... Chimpanzee Chimpanzees

Early History of Anthropoids Much of our knowledge about the early evolutionary history of anthropoids comes from fossils found in the Fayum district, a small desert area southwest of Cairo, Egypt During the Late Eocene and Oligocene, this region of Africa was a lush, tropical rain forest that supported a diverse and abundant fauna and flora

Within this forest lived many different arboreal anthropoids as well as various prosimians Thousands of Fossil Specimens In fact, several thousand fossil specimens representing more than 20 species of primates have been recovered from rocks of this region One of the earliest anthropoids, and a possible ancestor of the Old World monkeys, was Aegyptopithecus, a small, fruit-eating, arboreal primate

that weighed about 5 kg One of the Earliest Anthropoids Skull of Aegyptopithecus zeuxis, one of the earliest known anthropoids Anthropoid Superfamilies Anthropoids are divided into three

superfamilies Old World monkeys, New World monkeys, and hominoids Classification of Primates Order Primates: Suborder Prosimii: (lower primates) Lemurs, lorises, tarsiers, tree shrews Suborder Anthropoidea: (Higher primates Monkeys, apes, humans Superfamily Cercopithecoidea: Macaque, baboon,

proboscis monkey Superfamily Ceboidea: Howler, spider, and squirrel monkeys Superfamily Hominoidea: Apes, humans Family Pongidae: Chimpanzees, orangutans, gorillas Family Hylobatidae: Gibbons, siamangs Family Hominidae: Humans Old World Monkey Attributes Old World monkeys superfamily Cercopithecoidea

are characterized by close-set, downward-directed nostrils like those of apes and humans grasping hands, and a nonprehensile tail They include the macaque, baboon, and proboscis monkey

Old Word Monkey Superfamily Cercopithecoidea the Old World monkeys Old World Monkeys Distribution Present-day Old World monkeys

are distributed in the tropical regions of Africa and Asia and are thought to have evolved from a primitive anthropoid ancestor, such as Aegyptopithecus, sometime during the Oligocene New World Monkeys

New World monkeys superfamily Ceboidea are found only in Central and South America They probably evolved from African monkeys that migrated across the widening Atlantic

sometime during the Early Oligocene, and they have continued evolving in isolation to this present day New World Monkey New World Monkeys are members of the superfamily Ceboidea No Contact No evidence exists of any prosimian

or other primitive primates in Central or South America nor of any contact with Old World monkeys after the initial immigration from Africa New World monkeys are characterized by a prehensile tail, flattish face,

and widely separated nostrils and include the howler, spider, and squirrel monkeys Hominoids Hominoids superfamily Hominoidea consist of three families: the great apes family Pongidae which includes chimpanzees, orangutans, and gorillas

the lesser apes family Hylobatidae which are gibbons and siamangs; and the hominids family Hominidae which are humans and their extinct ancestors Hominoid Lineage The hominoid lineage diverged from Old World monkeys

sometime before the Miocene, but exactly when is still being debated It is generally accepted, however, that hominoids evolved in Africa, probably from the ancestral group that included Aegyptopithecus Climatic Shifts Recall that beginning in the Late Eocene the northward movement of the continents resulted in pronounced climatic shifts

In Africa, Europe, Asia, and elsewhere, a major cooling trend began, and the tropical and subtropical rain forests slowly began to change to a variety of mixed forests separated by savannas and open grasslands as temperatures and rainfall decreased Apes Adapted As the climate changed, the primate populations also changed

Prosimians and monkeys became rare, whereas hominoids diversified in the newly forming environments and became abundant Ape populations became reproductively isolated from each other within the various forests, leading to adaptive radiation and increased diversity among the hominoids Migration of Animals Possible

During the Miocene, Africa collided with Eurasia, producing additional changes in the climate, as well as providing opportunities for migration of animals between the two landmasses

Hominoid Relationships Two apelike groups evolved during the Miocene that ultimately gave rise to present-day hominoids Although scientists still disagree on the early evolutionary relationships among the hominoids, fossil evidence and molecular DNA similarities between modern hominoid families is providing a clearer picture of the evolutionary

pathways and relationships among the hominoids Dryopithecines The first group, the dryopithecines, evolved in Africa during the Miocene and subsequently spread to Eurasia, following the collision between the two continents The dryopithecines were a varied group of hominoids in size,

skeletal features, and life-style Proconsul The best-known dryopithecine and perhaps ancestor of all later hominoids is Proconsul, an ape-like fruit-eating animal that led a quadrupedal arboreal existence, with limited activity on the ground The dryopithecines were very abundant

and diverse during the Miocene and Pliocene, particularly in Africa Proconsul Probable appearance of Proconsul, a dryopithecine Sivapithecids The second group, the sivapithecids, evolved in Africa during the Miocene and then spread throughout Eurasia

The fossil remains of sivapithecids consist mostly of jaws, skulls, and isolated teeth There are few body or limb bones known, and thus we know little about their body anatomy Sivapithecids Ate Harder Foods All sivapithecids had powerful jaws and teeth with thick enamel and flat chewing surfaces, suggesting a diet of harder foods such as nuts Based on various lines of evidence,

the sivapithecids appear to be the ancestral stock from which present-day orangutans evolved Two Lineages Although many pieces are still missing, particularly during critical intervals

in the African hominoid fossil record, molecular DNA as well as fossil evidence indicates that the dryopithecines, African apes, and hominids form a closely related lineage The sivapithecids and orangutans form a different lineage that did not lead to humans Hominids The hominids (family Hominidae)

the primate family that includes present-day humans and their extinct ancestors have a fossil record extending back to almost 7 million years Several features distinguish them from other hominoids Hominids are bipedal; that is, they have an upright posture,

which is indicated by several modifications in their skeleton Comparison of Locomotion Comparison between quadrupedal and bipedal locomotion in gorillas and humans In gorillas the ischium bone is long

and the entire pelvis is tilted toward the horizontal Comparison of Locomotion Comparison between quadrupedal and bipedal locomotion in gorillas and humans In humans the ischium

bone is much shorter and the pelvis is vertical Larger Reorganized Brain In addition, hominids show a trend toward a large and internally reorganized brain An increase in brain size and organization is apparent in comparing the brains of a New World Monkey Larger Reorganized Brain

In addition, hominids show a trend toward a large and internally reorganized brain An increase in brain size and organization is apparent in comparing the brains of a great ape Larger Reorganized Brain In addition, hominids show a trend toward a large and internally reorganized brain An increase in brain size and organization

is apparent in comparing the brains of a present-day human Other Distinguishing Features Other features that distinguish hominids from other hominoids include

a reduced face and reduced canine teeth, omnivorous feeding, increased manual dexterity, and the use of sophisticated tools Response to Climatic Changes Many anthropologists think

these hominid features evolved in response to major climatic changes that began during the Miocene and continued into the Pliocene During this time, vast savannas replaced the African tropical rain forests where the lower primates and Old World monkeys had been so abundant

Mixed Forests and Grasslands As the savannas and grasslands continued to expand, the hominids made the transition from true forest dwelling to life to an environment

of mixed forests and grasslands No Clear Consensus At present, no clear consensus exists on the evolutionary history of the hominid lineage This is due in part

to the incomplete fossil record of hominids as well as new discoveries, and also because some species are known only from partial specimens or fragments of bone Because of this, scientists even disagree on the total number of hominid species Some Current Theories A complete discussion

of all the proposed hominid species and the various competing schemes of hominid evolution is beyond the scope of this course However, we will discuss the generally accepted taxa and present some of the current theories of hominid evolution Geologic Age Ranges The geologic age ranges

for the commonly accepted species of hominids Debates Remember that although the fossil record of hominid evolution is not complete, what does exist is well documented Furthermore, it is the interpretation of that fossil record that precipitates the often vigorous and sometimes acrimonious debates concerning our evolutionary history

Oldest Known Hominid Discovered in northern Chad's Djurab Desert in July, 2002,

the nearly 7-million-year-old skull and dental remains of Sahelanthropus tchadensis make it the oldest known hominid yet unearthed and very close to the time when humans diverged from our closest-living relative, the chimpanzee Leg Bones and Feet Needed Sahelanthropus tchadensis may have been bipedal in its walking habits, but until bones from its legs and feet are found, that supposition remains conjecture

Next Oldest Hominid The next oldest hominid is Orrorin tugenensis, whose fossils have been dated at six million years and consist of bits of jaw, isolated teeth, finger, arm, and partial upper leg bones At this time, debate continues as to exactly where Orrorin tugenensis fits in the hominid lineage Ardipithecus ramidus

Sometime between 5.8 and 5.2 million years ago, another hominid was present in eastern Africa Ardipithecus ramidus kadabba is older than its 4.4 million year old relative Ardipithecus ramidus ramidus Ardipithecus ramidus kadabba is very similar in most features to Ardipithecus ramidus ramidus but in certain features of its teeth is more apelike than its younger relative

Geologic Age Ranges The geologic age ranges for the commonly accepted species of hominids Habitual Bipedal Walkers Although many paleoanthropologists think both Orrorin tugenensis and Ardipithecus ramidus kadabba were habitual bipedal walkers and thus on a direct evolutionary line to humans, others are not as impressed with the fossil evidence

and are reserving judgment Until more fossil evidence is found and analyzed, any single scheme of hominid evolution presented here would be premature Australopithecines Australopithecine is a collective term for all members of the genus Australopithecus Currently, five species are recognized:

A. anamensis, A. afarensis, A. africanus, A. robustus, and A. boisei

Evolutionary Scheme Many paleontologists accept the evolutionary scheme in which A. anamensis, the oldest known australopithecine, is ancestral to A. afarensis, who in turn is ancestral to A. africanus and the genus Homo, as well as the side branch of australopithecines represented by A. robustus and A. boisei

Oldest Known Australopithecine The oldest known australopithecine is Australopithecus anamensis and was discovered at Kanapoi, a site near Lake Turkana, Kenya, by Meave Leakey of the National Museums of Kenya and her colleagues Similar Yet More Primitive

A. anamensis, a 4.2-million-year-old bipedal species, has many features in common with its younger relative, A. afarensis, yet is more primitive in other characteristics, such as its teeth and skull

A. anamensis is estimated to have been between 1.3 and 1.5 m tall and weighed between 33 and 50 kg Australopithecus afarensis Australopithecus afarensis, which lived 3.93.0 million years ago, was fully bipedal and exhibited great variability in size and weight Members of this species ranged

from just over 1 m to about 1.5 m tall and weighed between 29 and 45 kg Lucy A reconstruction of Lucys skeleton This reconstruction by Owen Lovejoy and his students at Kent

State University, Ohio Lucy is an ~ 3.5-millionyear-old Australopithecus afarensis illustrates how adaptations in individual whose fossil remains were discovered by Donald Johanson Lucys hip, leg and foot allowed a fully bipedal

means of locomotion Hominid Footprints Preserved in volcanic ash at Laetoli, Tanzania Discovered in 1978 by Mary Leakey, these footprints proved hominids were bipedal walkers at least 3.5 million years ago The footprints of two

adults and possibly those of a child are clearly visible in this photograph Hominid Footprints Most scientists think the footprints were made by Australopithecus afarensis

whose fossils are found at Laetoli Brain Size of A. afarensis A. afarensis had a brain size of 380450 cubic centimeters (cc), larger than the 300400 cc of a chimpanzee but much smaller than that of present-day humans (1350 cc average) Apelike Features

The skull of A. afarensis retained many apelike features, including massive brow ridges and a forward-jutting jaw, but its teeth were intermediate between those of apes and humans

The heavily enameled molars were probably an adaptation to chewing fruits, seeds, and roots Landscape with A. afarensis Re-creation of a Pliocene landscape showing members of

Australopithecus afarensis gathering and eating various fruits and seeds A. africanus Lived 3.02.3 mya A. afarensis was succeeded by Australopithecus africanus, which lived 3.02.3 million years ago

The differences between the two species are relatively minor They were both about the same size and weight, but A. africanus had a flatter face and somewhat larger brain Skull of A. africanus A reconstruction of the skull of Australopithecus

africanus This skull, known as that of the Taung Child, was discovered by Raymond Dart in South Africa in 1924 and marks the beginning of modern paleoanthropology

Not As Well Adapted for Bipedalism It appears the limbs of A. africanus may not have been as well adapted for bipedalism as those of A. afarensis Robust Species Both A. afarensis and A. africanus differ markedly from the so-called robust species A. boisei (2.61.0 million years ago)

and A. robustus (2.01.2 million years ago) A. boisei was 1.21.4 m tall and weighed between 34 and 49 kg It had a powerful upper body, a distinctive bony crest on the top of its skull, a flat face, and the largest molars of any hominids A. robustus Was a Vegetarian A. robustus, in contrast, was somewhat smaller (1.11.3 m tall)

and lighter (3240 kg) It had a flat face, and the crown of its skull had an elevated bony crest that provided additional area for the attachment of strong jaw muscles Its broad flat molars indicated A. robustus was a vegetarian Australopithecus robustus Skull The skull of

Australopithecus robustus This species had a massive jaw, powerful chewing muscles, and large broad flat chewing teeth apparently used for grinding up coarse plant food

Separate Lineage Most scientists accept the idea that the robust australopithecines form a separate lineage from the other australopithecine that went extinct 1 million years ago

The Human Lineage Homo habilis The earliest member of our own genus Homo is Homo habilis, which lived 2.5-1.6 million years ago Its remains were first found at Olduvai Gorge, but it is also known from Kenya, Ethiopia, and South Africa H. habilis evolved from the A. afarensis and A. africanus lineage

and coexisted with A. africanus for about 200,000 years Geologic Age Ranges The geologic age ranges for the commonly accepted species of hominids Characteristics of Homo habilis H. habilis had a larger brain (700 cc average) than its australopithecine ancestors, but smaller teeth

It was about 1.2-1.3 m tall and only weighed 32-37 kg Homo Erectus In contrast to the australopithecines and H. habilis, which are unknown outside Africa, Homo erectus was a widely distributed species, having migrated from Africa during the Pleistocene Specimens have been found not only in Africa

but also in Europe, India, China ("Peking Man"), and Indonesia ("Java Man") Survived in Asia Until About 100,000 Years Ago H. erectus evolved in Africa 1.8 million years ago and by 1 million years ago was present in southeastern and eastern Asia, where it survived until about 100,000 years ago H. erectus Differed From

Modern Humans Although H. erectus developed regional variations in form, the species differed from modern humans in several ways Its brain size of 800-1300 cc, though much larger than that of H. habilis, was still less than the average for Homo sapiens (1350 cc) Size Similar to Humans

H. erectus's skull was thick-walled, its face was massive, it had prominent brow ridges, and its teeth were slightly larger than those of present-day humans H. erectus was comparable to size to modem humans, standing between 1.6 and 1.8 m tall and weighing between 53 and 63 kg Skull of Homo erectus

A reconstruction of the skull of Homo erectus a widely distributed species whose remains have been found in Africa, Europe, India, China, and Indonesia H. erectus Was a Tool Maker

The archaeological record indicates that H. erectus was a tool maker Furthermore, some sites show evidence that its members used fire and lived in caves, an advantage for those living in more northerly climates Homo erectus Using Tools Re-creation of a Pleistocene setting in Europe in which members of Homo erectus are

using fire and stone tools The "Out of Africa" View Currently, a heated debate surrounds the transition from H. erectus to our own species, Homo sapiens Paleoanthropologists are split into two camps On the one side are those who support the "out of Africa" view According to this camp, early modern humans

evolved from a single woman in Africa, whose offspring then migrated from Africa, perhaps as recently as 100,000 years ago and populated Europe and Asia, driving the earlier hominid populations to extinction The "Multiregional" View On the other side are those supporting the "multiregional" view According to this hypothesis, early modern humans did not have an isolated

origin in Africa, but rather established separate populations throughout Eurasia Occasional contact and interbreeding between these populations enabled our species to maintain its overall cohesiveness, while still preserving the regional differences in people we see today Homo sapiens Evolved From H. erectus

Regardless of which theory turns out to be correct, our species, H. sapiens most certainly evolved from H. erectus Neaderthals Perhaps the most famous of all fossil humans are the Neanderthals, who inhabited Europe and the Near East from about 200,000 to 30,000 years ago Some paleoanthropologists regard the

Neanderthals as a variety or subspecies of our own species (Homo sapiens neanderthalensis), whereas others regard them as a separate species (Homo neanderthalensis) Specimens Found in Neander Valley In any case, their name comes from the first specimens found in 1856 in the Neander Valley near Dsseldorf, Germany

Neanderthals Difference The most notable difference between Neanderthals and present-day humans is in the skull Neanderthal skulls were long and low with heavy brow ridges, a projecting mouth, and a weak, receding chin Their brain was slightly larger on average than our own, and somewhat differently shaped

Neanderthal Skull Reconstructed Neanderthal skull The Neanderthals were characterized by prominent heavy brow ridges and week chin Cold Adapted

The Neanderthal body was somewhat more massive and heavily muscled than ours, with rather short lower limbs,

much like those of other cold-adapted people of today First Humans in Cold Climates Given the specimens from more than 100 sites, we now know Neanderthals were not much different from us, only more robust Europe's Neanderthals were the first humans to move into truly cold climates, enduring miserably long winters and short summers

as they pushed north into tundra country Burial Ceremony in a Cave Archaeological evidence indicates Neanderthals lived in caves and participated in ritual burials as depicted in this painting of a burial ceremony such as occurred approximately 60,000 years ago at Shanidar Cave, Iraq Took Care of Their Injured

The remains of Neanderthals are found chiefly in caves and hutlike rock shelters, which also contain a variety of specialized stone tools and weapons Furthermore, archaeological evidence indicates

that Neanderthals commonly took care of their injured and buried their dead, frequently with such grave items as tools, food, and perhaps even flowers Cro-Magnons About 30,000 years ago,

humans closely resembling modern Europeans moved into the region inhabited by the Neanderthals and completely replaced them Cro-Magnons, the name given to the successors of the Neanderthals in France, lived from about 35,000 to 10,000 years ago; during this period the development of art and technology far exceeded anything the world had seen before Nomadic Hunters

Highly skilled nomadic hunters, Cro-Magnons followed the herds in their seasonal migrations They used a variety of specialized tools in their hunts, including perhaps the bow and arrow They sought refuge in caves and rock shelters and formed living groups of various sizes Cro-Magnon Camp Re-creation of a Cro-Magnon camp in Europe

Cave Painters Cro-Magnons were also cave painters Using paints made from manganese and iron oxides, Cro-Magnon people painted hundreds of scenes on the ceilings and walls of caves

in France and Spain, where many of them are still preserved today Painting From a Cave in France Cro-Magnons were very skilled cave painters Painting of a horse from the cave of Niaux, France Cultural Evolution With the appearance of Cro-Magnons, human evolution has become

almost entirely cultural rather than biological Humans have spread throughout the world by devising means to deal with a broad range of environmental conditions Since the evolution of the Neanderthals

about 200,000 years ago, humans have gone from a stone culture to a technology that has allowed us to visit other planets with space probes and land astronauts on the Moon Future It remains to be seen

how we will use this technology in the future and whether we will continue as a species, evolve into another species, or become extinct as many groups have before us Summary The primates evolved during the Paleocene Several trends help characterize primate and differentiate them from other mammalian orders,

including a change in overall skeletal structure and mode of locomotion an increase in brain size stereoscopic vision and evolution of a grasping hand with opposable thumb Summary The primates are divided into two suborders the prosimians and the anthropoids The prosimians are the oldest primate lineage

and include lemurs, lorises, tarsiers, and tree shrews The anthropoids include the New and Old World monkeys, apes, and hominids, which are humans and their extinct ancestors Summary The oldest known hominid is Sahelanthropus tchadensis,

dated at nearly 7 million years then two subspecies of Ardipithecus at 5.8 and 4.4 million years respectively These early hominids were succeeded by the australopithecines a fully bipedal group that evolved in Africa 4.2 million years ago Summary Currently, five australopithecine species are known:

Australopithecus anamensis, A. afarensis, A. africanus, A. robustus and A. boisei The human lineage began about 2.5 million years ago in Africa with the evolution of Homo habilis, which survived as a species

until about 1.6 million years ago Homo erectus evolved from habilis about 1.8 million years ago and was the first hominid to migrate out of Africa Summary Between 1 and 1.8 million years ago, H. erectus had spread to Europe, India, China, and Indonesia

H. erectus used fire, made tools, and lived in caves Sometime between 200,000 and 100,000 years ago Homo Sapiens evolved from H. erectus These early humans may be ancestors of Neaderthals Summary Neanderthals were not much different from present-day humans,

only more robust and with differently shaped skulls They made specialized tools and weapons, apparently took care of their injured, and buried their dead The Cro-Magnons were the successors of the Neanderthals and lived from about 35,000-10,000 years ago Summary

Cro-Magnons were highly skilled nomadic hunters, formed living groups of various sizes, and were also skilled cave painters Modern humans succeeded the Cro-Magnons about 10,000 years ago and have spread throughout the world

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