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What You’ll Learn■ You will compare and

contrast primates and theiradaptations.

■ You will analyze the evidencefor the ancestry of humans.

Why It’s ImportantHumans are primates. A knowl-edge of primates and their evolution can provide an under-standing of human origins.

Primate EvolutionPrimate Evolution

National Geographic Image Society Collection

Visit to• study the entire chapter

online• access Web Links for more

information and activities onprimate evolution

• review content with theInteractive Tutor and self-check quizzes

Humans are not the only animalsthat use tools. This chimpanzee isusing a stone to crack a nutshell.

Understandingthe Photo

ca.bdol.glencoe.com

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16.1

What is a primate?Have you ever gone to a zoo and seen monkeys, chimpanzees, gorillas,

or baboons? If you have, then you’ve observed some different types ofprimates. The primates are a group of mammals that includes lemurs,monkeys, apes, and humans. Primates come in a variety of shapes andsizes, but, despite their diversity, they share common traits. Learn moreabout primates on pages 1068–1069 in the Focus On.

What characteristics account for the complex behaviors of primates?Find out by reading Figure 16.1 on the next page. Primates have roundedheads with flattened faces, unlike most other mammals. Fitting snuglyinside the rounded head is a brain that, relative to body size, is the largestbrain of any terrestrial mammal. Primate brains are also more complexthan those of other animals. The diverse behaviors and social interactionsof primates reflect the complexity of their brains.

The majority of primates are arboreal, meaning they live in trees, andhave several adaptations that help them survive there. All primates haverelatively flexible shoulder and hip joints. These flexible joints are impor-tant to some primates for climbing and swinging among branches.

16.1 PRIMATE ADAPTATION AND EVOLUTION 421

Primate Adaptation and Evolution

SECTION PREVIEWObjectivesRecognize the adaptationsof primates.Compare and contrastthe diversity of living primates.Distinguish the evolu-tionary relationships ofprimates.

Review Vocabularyspeciation: the process of

evolution of a newspecies that occurswhen members of simi-lar populations nolonger interbreed toproduce fertile offspring (p. 409)

New Vocabularyprimateopposable thumbanthropoidprehensile tail

Illustrate and Label As you read Chapter 16, identify the characteristics of each group of primates under the appropriate tab.

Investigating Primates Make the following Foldable to help you organize information about the two groups of primates.

Fold a sheet of paper in half lengthwise. Make the back edge about 2 cm longer than the front edge.

Turn the paper so the fold is on the bottom. Then fold it in half.

Unfold and cut only the top layer along the fold to make two tabs.

Label the Foldable as shown.

STEP 1

STEP 3

STEP 2

STEP 4

Strepsirrhines Haplorhines

Primates

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422 PRIMATE EVOLUTIONMack Henry/Visuals Unlimited

Brain volume A primate’s brainvolume is large relative to its bodysize. The complex behaviors of aprimate reflect its large brain.

CCOpposablethumbs Theprimate’s oppos-able thumbsenable it to graspand manipulateobjects. The thumbis also flexible,which increasesthe primate’sability to mani-pulate objects.

AA

Arm movement The shoulders of aprimate are adapted for arm movementin different directions. Flexible armmovement is an important advantagefor arboreal primates.

DD

Flexible jointsThe flexible joints in aprimate’s elbow and wristallow the primate to turn itshand in many directions.

EEFeet A primate’s feet cangrasp objects. However, primateshave different degrees ofefficiency for grasping objectswith their feet.

FF

A PrimateFigure 16.1Primates are a diverse group of mammals, but they sharesome common features. For example, you can see in thedrawing of a gibbon that primates have rounded heads andflattened faces, unlike most other groups of mammals.Critical Thinking Why would binocular vision be an adaptive advantage for primates?

Vision Vision is the dominant sense in aprimate. In addition to good visual perception,a primate has binocular vision, which provides itwith a stereoscopic view of its surroundings.

BB

Gibbon

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Primate hands and feet are uniqueamong mammals. Their digits, fingersand toes, have nails rather than clawsand their joints are flexible. In addition,primates have an opposable thumb—a thumb that can cross the palm to meetthe other fingertips. Opposable thumbsenable primates to grasp and cling toobjects, such as the branches of trees.Primates can also hold and manipulatetools, as shown in Figure 16.2.

Primates have a highly developedtype of vision, called binocular vision.Primate eyes face forward so that theysee an object simultaneously from two viewpoints, or through both eyes.This positioning of the eyes enablesprimates to perceive depth and thusgauge distances. As you might imag-ine, this type of vision is helpful for ananimal jumping from tree to tree.Primates also have color vision thataids depth perception, enhances theirability to detect predators, and helpsthem find ripe fruits.

List some commoncharacteristics of primates.

Primate OriginsThe similarities among the many

primates is evidence that primates

share an evolutionary history. Scientistsuse fossil evidence and comparativeanatomical, genetic, and biochemicalstudies of modern primates to proposeideas about how primates are relatedand how they evolved. Biologists clas-sify primates into two major groups:strepsirrhines and haplorhines, asshown in Figure 16.3.

Primates Present-day strepsirrhines are

small primates that include, amongothers, the lemurs and aye-ayes. Moststrepsirrhines have large eyes and arenocturnal. They live in the tropicalforests of Africa and Southeast Asia.The earliest fossils of strepsirrhinesare about 50 to 55 million years old.

16.1 PRIMATE ADAPTATION AND EVOLUTION 423

anthropoid fromthe Greek wordsanthropos, mean-ing “man,” andeidos, meaning“shape”; Theanthropoid apesresemble humans in their generalappearance.

Carolina Biological Supply/Phototake, NYC

Figure 16.2Chimpanzees haveopposable thumbs tohelp them grasp andcling to objects andmanipulate them.

Primate Ancestors

Anthropoids

Haplorhines

Hominoids

New World monkeys

Tarsiers

Lemurs Lorises, Pottos,and Galagos

African apes

OrangutansGibbons

Humans

Old World monkeys

Hominids

Strepsirrhines

Figure 16.3Primates are dividedinto two groups: thestrepsirrhines and thehaplorhines, which aresubdivided into OldWorld monkeys, NewWorld monkeys, andhominoids.

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Some scientists consider fossils ofan organism called Purgatorius to bethe earliest of primate fossils.Purgatorius, which probably resem-bled a squirrel, was a strepsirrhinelikeanimal that lived about 66 millionyears ago. Although there are no liv-ing species of Purgatorius, present-daystrepsirrhines, Figure 16.4, are quitesimilar.

Humanlike primates evolveThe remaining living primates are

members of a group called hap-lorhines. This group consists of tar-siers and the anthropoids (AN thruhpoydz), the humanlike primates.Anthropoids include hominoids andOld and New World monkeys, asshown in Figure 16.5. In turn,hominoids include apes and humans.

424 PRIMATE EVOLUTION

Figure 16.5Monkeys and homi-noids are classifiedas anthropoids.

Golden liontamarins arearboreal NewWorld monkeysthat live in SouthAmerica.

A

This mandrill is an Old World monkey thatlives in the forests of West Africa, andspends most of its time on the ground.

B

The aye-aye, a primate found in Madagascar,uses its long middle finger to dig for grubs.

A

Tarsiers are pri-mates that live in the Philippines,

Borneo, andSumatra.

B

Figure 16.4Most basal primates are small,nocturnal animals that live intropical environments.

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Many features characterize anthro-poids. Anthropoids have more complexbrains than strepsirrhines. Anthropoidsare also larger and have different skele-tal features, such as a more or lessupright posture, than strepsirrhines.

What are commonly called “mon-keys” are classified as either NewWorld monkeys or Old World mon-keys. New World monkeys, which livein the rain forests of South Americaand Central America, are all arbor-eal. A long, muscular prehensile(pree HEN sul) tail characterizes manyof these primates. They use the tail asa fifth limb, grasping and wrapping itaround branches as they move fromtree to tree. Among the New Worldmonkeys are tiny marmosets andlarger spider monkeys.

Old World monkeys are generallylarger than New World monkeys.They include the arboreal monkeys,such as the colobus monkeys andguenons, the terrestrial monkeys,such as baboons, and monkeys, suchas macaques, which are equally athome in trees or on the ground. OldWorld monkeys do not have prehen-sile tails. They are adapted to manyenvironments that range from thehot, dry savannas of Africa to the coldmountain forests of Japan.

Hominoids are classified as apes or humans. Apes include orangutans,gibbons, chimpanzees, bonobos, andgorillas. Apes lack tails and have dif-ferent adaptations for arboreal lifefrom those of the strepsirrhines andmonkeys. For example, apes havelong, muscled forelimbs for climbingin trees, swinging from branches, andknuckle walking, or walking on twolegs with support from their hands.Try the MiniLab shown here to inves-tigate an adaptation for tree climbing.Although many apes are arboreal,most also spend time on the ground.Gorillas, the largest of the apes, live

in social groups on the ground.Among the apes, social interactionsindicate a large brain capacity.

Humans have an even larger braincapacity and walk upright. You willread more about human primates inthe next section. Anthropologists havesuggested that monkeys, apes, andhumans share a common anthropoidancestor based on their structural andsocial similarities. Use the Problem-Solving Lab on the next page to explorethis idea. The oldest anthropoid fossils

16.1 PRIMATE ADAPTATION AND EVOLUTION 425Matt Meadows

InferHow useful is an opposablethumb? Have you everthought about what makesyou different from othermammals as diverse as cowsand dogs? One key differ-ence between primates likeyou and the other mammalsis that you have opposablethumbs. You may not live intrees like some other primates,but this adaptation is useful in avariety of additional ways. In thisactivity, you will explore the impor-tance of your thumbs.

Procedure! Loosely wrap your dominant hand with tape so that your

thumb points in the same direction as your fingers.@ Try to pick up a pen and write a sentence.# Pick up your textbook and hand it to another student.$ Pitch a tennis ball into an empty trash can two meters away.% Repeat steps 2–4 after unwrapping your hand.

Analysis1. Compare Describe the results of your performance with

the absence of an opposable thumb and with one. 2. Infer Why is an opposable thumb an important adapta-

tion for primates?3. Use Models Design models for completing three simple

tasks without using your thumb, such as turning a door-knob or switching on a light.

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are from Africa and Asia and date toabout 37 to 40 million years ago.

Anthropoids evolved worldwideThe oldest monkey fossils are of

New World monkeys and are 30 to 35 million years old. AlthoughNew World monkeys probably sharea common anthropoidlike ancestorwith the Old World monkeys, theyevolved independently of the OldWorld monkeys because of geo-graphic isolation. In Figure 16.6, youcan see the worldwide geographic dis-tribution of monkeys and apes.

Old World monkeys evolved morerecently than New World monkeys.Scientists suspect this is true becausethe oldest fossils of Old World monkeys are only about 20 to 22 mil-lion years old. The fossils indicatethat the earliest Old World mon-keys were arboreal like today’s NewWorld monkeys.

Hominoids evolved in Asia and Africa

According to the fossil record,there was a global cooling when thehominoids evolved in Asia and Africa.Important changes in vegetation,

426 PRIMATE EVOLUTION

New Worldmonkeys

Gorillas

Old Worldmonkeys

Gibbons

Chimpanzees

Figure 16.6The present-day, world-wide distribution ofmonkeys and apes showsthey have adapted to awide range of habitats.Interpret ScientificIllustrations Whichgroup has the widestmodern distribution?The most restricteddistribution?

Use NumbersHow do primate infants and adults compare? Someinfant primates, such as macaques, cling to their mothers fortheir first few months of life. Therefore, muscles associatedwith clinging may represent a higher percentage of total bodyweight in infant macaques than in adult macaques.

Solve the ProblemThe graph shows the percentages of body weight for specific body parts of adult and infant macaques.

Thinking Critically1. Compare Explain the difference between the percentage

of body weight of infant heads and adult heads.2. Hypothesize Explain why the percentage of body weight

for hands and feet changes as macaques mature. Would youexpect the same pattern in humans? Explain your answer.

Macaque Body Weight Percentages

10

20

30

40

50

Perc

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of b

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wei

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Infant macaque

Trunk Head Upper limb

Hand Lowerlimb

Foot

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such as the evolution of grass, alsooccurred. At about the same time, theOld World monkeys became adaptedto this climatic cooling. Fossils indi-cate how the apes adapted and diver-sified. You can see two examples ofthe present-day diversity of apes inFigure 16.7.

Remember that hominoids includethe apes and humans. By examiningthe DNA of each of the modernhominoids, scientists have evaluated

the probable order in which the dif-ferent apes and humans evolved.From this type of evaluation, itappears that gibbons were probablythe first apes that evolved, followedby the orangutans that are found insoutheast Asia. Finally, the Africanapes, gorillas and chimpanzees,evolved. Morphological and molecu-lar data suggest that chimpanzeesshare the closest common ancestorwith modern humans.

Understanding Main Ideas1. What adaptations help primates live in the trees?2. What features distinguish anthropoids from

strepsirrhines?3. Draw a concept map to illustrate one possible

pathway for the evolutionary history (phylogeny)of hominoids.

Thinking Critically4. Imagine you are a world famous primatologist, a

scientist who studies primates. An unidentified,

complete fossil skeleton arrives at your lab. You suspect that it’s a primate fossil. What observations would you make to determine if your suspicions are accurate?

5. Get the Big Picture Make a table listing the dif-ferent types of primates, key facts about eachgroup, and how the groups might be related. Formore help, refer to Get the Big Picture in the Skill Handbook.

SKILL REVIEWSKILL REVIEW

16.1 PRIMATE ADAPTATION AND EVOLUTION 427(l)Conpost/Visage/Peter Arnold, Inc., (r)M. Gunther/Peter Arnold, Inc.

AA

BB

ca.bdol.glencoe.com/self_check_quiz

Figure 16.7Modern apes are diverse, and fossils indicatethat ancient apes were even more diverse.Orangutans are arboreal apes that live in theforests of Borneo and Sumatra (A). Gorillas areground-dwelling African apes that live in smallsocial groups (B).

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16.2SECTION PREVIEWObjectivesCompare and contrastthe adaptations of aus-tralopithecines with thoseof apes and humans.Identify the evidence ofthe major anatomicalchanges in hominids dur-ing human evolution.

Review Vocabularyfossil: evidence of an

organism that lived longago that is preserved inEarth’s rocks (p. 370)

New VocabularyhominoidbipedalhominidaustralopithecineNeandertalCro-Magnon

428 PRIMATE EVOLUTION

Solving a PuzzleUsing Prior Knowledge Have youever tried to put together a jigsawpuzzle and found that some of thepieces were missing? If several piecesare lost, it is difficult to figure outwhat the puzzle is a picture of.Sometimes it depends on which partof the puzzle is missing. If the puzzleis a picture of a famous person andpieces of the face are missing, it’shard to tell who it is. But if the missing pieces are part of the back-ground, you can still identify theperson. Scientists who study human ancestry try to fit together a puzzlefrom scattered pieces of fossils—a puzzle with most of the pieces missing!Infer What parts of a skeleton do you think would provide scientists with themost information? Explain your answer.

HominidsSome scientists propose that between 5 and 8 million years ago in

Africa, a population that was ancestral to chimpanzees and humansdiverged into two lines. According to this hypothesis, one line evolvedinto chimpanzees, and the other line eventually evolved into modernhumans. These two lines are collectively called the hominoids(HAH mih noydz)—primates that can walk upright on two legs andinclude gorillas, chimpanzees, bonobos, and humans. There are rela-tively few fossils to support this hypothesis, but DNA studies of themodern hominoids provide data that support the idea. You can workwith some of these data in MiniLab 16.2 on the next page.

Some scientists suggest that the divergence of the population of ances-tral hominoids might have occurred in response to environmentalchanges that forced some ancestral hominoids to leave their treetopenvironments and move onto the ground to find food. In order to moveefficiently on the ground while avoiding predators, it was helpful for thehominoids to be bipedal, meaning able to walk on two legs. Hominids(HAH mih nudz) are bipedal primates that include modern humans andtheir direct ancestors. In addition to increased speed, walking on twolegs leaves the arms and hands free for other activities, such as feeding,protecting young, and using tools. Therefore, hominoids with the abil-ity to walk upright probably survived more successfully on the ground.

Human Ancestry

John Reader/Science Photo Library/Photo Researchers

Homo habilis skull

Standard 1k Students will recognize the cumulative nature of scientificevidence.

California Standards

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These individuals then lived to repro-duce and pass the characteristics totheir offspring. According to this rea-soning, the bipedal organisms thatevolved might have been the earliesthominids.

Although the fossil record isincomplete, more hominid fossils arefound every year. The many fossilsthat scientists have found revealmuch about the anatomy and behav-ior of early hominids. Fossils of skullsprovide scientists with informationabout the appearance and braincapacity of the early hominid types.Complete the BioLab at the end ofthe chapter to learn more about thekinds of information scientists gatherfrom skulls of hominids.

Early hominids walked uprightIn Figure 16.8, you see a South

African anatomist, Raymond Dart, who,in 1924, discovered a skull of a younghominoid with a braincase and facialstructure similar to those of an ape.

16.2 HUMAN ANCESTRY 429John Reader/Science Photo Library/Photo Researchers

Figure 16.8Raymond Dart discovered the first australo-pithecine fossil, the Taung child, Australopi-thecus africanus. The skull has features ofboth apes and humans.

Analyze InformationCompare Human Proteins with Those of Other PrimatesScientists use differences in amino acid sequences in proteinsto determine the evolutionary relationships of living species.In this activity, you’ll compare representative short sequencesof the amino acids of a specific protein among groups of pri-mates to determine their evolutionary history.

Procedure! Prepare a data table.@ For each primate listed in the table above, determine

how many amino acids differ from the human sequence.Record these numbers in the data table.

# Calculate the percentage differences by dividing the num-bers by 15 and multiplying by 100. Record the numbers inyour data table.

Analysis1. Interpret Data Which primate is most closely related to

humans? Least closely related?2. Formulate Models Construct a diagram of primate evo-

lutionary relationships that most closely fits your results.

Amino Acid Sequences in Primates

Baboon Chimp Lemur Gorilla Human

ASN SER ALA SER SER

THR THR THR THR THR

THR ALA SER ALA ALA

GLY GLY GLY GLY GLY

ASP ASP GLU ASP ASP

GLU GLU LYS GLU GLU

VAL VAL VAL VAL VAL

ASP GLU GLU GLU GLU

ASP ASP ASP ASP ASP

SER THR SER THR THR

PRO PRO PRO PRO PRO

GLY GLY GLY GLY GLY

GLY GLY SER GLY GLY

ASN ALA HIS ALA ALA

ASN ASN ASN ASN ASN

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However, the skull also had an unusualfeature for an ape skull—the positionof the foramen magnum, the opening inthe skull through which the spinalcord passes as it leaves the brain.

In the fossil, the opening was locatedon the bottom of the skull, as it is inhumans but not in apes. Because of thisfeature, Dart proposed that theorganism had walked upright. He clas-sified the organism as a new primatespecies, Australopithecus africanus (awstray loh PIH thuh kus • a frih KAH nus),which means “southern ape fromAfrica.” The skull that Dart found hasbeen dated at between 2.5 and 2.8million years old.

Since Dart’s discovery, paleoanthro-pologists, scientists who study humanfossils, have recovered many more australopithecine specimens. Theydescribe an australopithecine as anearly hominid that lived in Africa andpossessed both apelike and humanlikecharacteristics.

Early hominids: Apelike and humanlike

Later, in East Africa in 1974, an American paleoanthropologist,Donald Johanson, discovered one ofthe most complete australopithecineskeletons that he called “Lucy.”Radiometric dating shows that Lucyprobably lived about 3.2 millionyears ago. Johanson proposed thatthe Lucy skeleton was a new species,Australopithecus afarensis. Other fos-sils of A. afarensis indicate that thisspecies probably existed between 3 and 4 million years ago.

Although the fossils show that A. afarensis individuals had apelikeshoulders and forelimbs, the structureof the pelvis, as shown in Figure 16.9,indicates that these individuals werebipedal, like humans. On the otherhand, the size of the braincase sug-gests that their brains had a small,apelike volume and not a largerhuman volume.

430 PRIMATE EVOLUTION

paleoanthropologyfrom the Greekwords paleo, meaning “ancient,”anthropo, meaning“human,” andlogos, meaning“study”; Paleo-anthropology is the study ofhuman fossils.

Figure 16.9Some skeletal fea-tures of an aus-tralopithecine areintermediatebetween those ofmodern apes andhumans. Comparethe skull andpelvic bone ofAustralopithecusafarensis (B) withthose of the chim-panzee (A) andthe human (C).

ChimpanzeePan Troglodytes

Ancient HominidAustralopithecus afarensis

HumanHomo Sapiens

Ischialtuberosity

Acetabulum

Ilium

Ischialtuberosity

Ilium

Ischialtuberosity

Ilium

Acetabulum Acetabulum

AA BB CC

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You may be wondering what lifewas like for hominids like Lucy.Because of the combination of apelikeand humanlike features, one idea isthat A. afarensis and other species ofaustralopithecines might have lived insmall family groups, sleeping and eat-ing in trees. But, to travel, theywalked upright on the ground. Thefossil record indicates that an A. afarensis individual rarely survivedlonger than 25 years.

In addition to fossils of A. afarensisand A. africanus, fossils of three orperhaps four other species of aus-tralopithecines have been found.These other species, discovered inEast Africa and South Africa, aredated from about 2.5 to 4.3 millionyears old. Three other species ofhominids have been found that aresimilar to australopithecines. Theseearlier hominids are grouped into thegenus Paranthropus because their fos-sils suggest that they had larger teethand jaws and sturdier bodies than australopithecines.

The relationships among austra-lopithecines are not entirely clearfrom the fossil record. However, thegenus disappears from the recordbetween 2.0 and 2.5 million years ago.Although australopithecines becameextinct, some paleoanthropologistspropose that an early population ofthese hominids might have beenancestral to modern humans.

Identify the differ-ences in fossil hominid species usinganatomical evidence.

The Emergence ofModern Humans

Any ideas about the evolution ofmodern hominids must include howbipedalism and a large brain evolved.Australopithecine fossils provide

support for the idea that bipedalismevolved first. But when did a largebrain evolve in a hominid species?When did hominids begin to usetools and develop culture?

Early members of the genusHomo made stone tools

In 1964, anthropologists Louis andMary Leakey, Figure 16.10, describedskull portions belonging to anothertype of hominid in Tanzania, Africa.This skull was more humanlike thanthose of australopithecines. In partic-ular, the braincase was larger and theteeth and jaws were smaller, more likethose of modern humans. Because ofthe skull’s human similarities, theLeakeys classified the hominid withmodern humans in the genus Homo.Because stone tools were found nearthe fossil skull, they named thespecies Homo habilis, which means“handy human.”

Radiometric dating indicates that H. habilis lived between about 1.5 and2.5 million years ago. It is the earliestknown hominid to make and use stonetools. These tools suggest that H.habilis might have been a scavengerwho used the stone tools to cut meatfrom carcasses of animals that had beenkilled by other animals. You can see aH. habilis skull in Figure 16.11 on thenext page.

16.2 HUMAN ANCESTRY 431Des Bartlett/Photo Researchers

Figure 16.10Mary and Louis Leakeydiscovered many fossilsin the Olduvai Gorgearea of Tanzania,Africa. Describe Whywas the Leakeys’ dis-covery of Homohabilis important?

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Hunting and using fireSome anthropologists propose that

a H. habilis population or anotherspecies, Homo ergaster, gave rise to anew species about 1.5–1.8 millionyears ago. This new hominid specieswas called Homo erectus, which means“upright human.” H. erectus had alarger brain and a more humanlikeface than H. habilis. However, it hadprominent browridges and a lowerjaw without a chin, as shown inFigure 16.12, which are apelike characteristics.

Some scientists interpret the stonetools called hand axes that they find atsome H. erectus excavation sites as anindication that H. erectus hunted. Incaves at these sites, they have alsofound hearths with charred bones.This evidence suggests that thesehominids used fire and lived in caves.

The distribution of fossils indicatesthat H. erectus migrated from Africaabout 1 million years ago. Then thishominid spread through Africa andAsia, and possibly migrated intoEurope, before becoming extinctbetween 130 000 and 300 000 yearsago. However, some scientists pro-pose that more human-lookinghominids might have arisen from H. erectus before it disappeared.

432 PRIMATE EVOLUTION(tl)Frank T. Aubrey/Visuals Unlimited, (tr)AKG Photo, London, (bl)National Museum of Kenya/Visuals Unlimited

Figure 16.12A nearly completeHomo erectus skele-ton of a young malewas discovered inEast Africa in 1985(A). H. erectus had a brain volume ofabout 1000 cm3

and long legs likemodern humans (B).

Homo erectus

Figure 16.11The average brain volumeof Homo habilis was 600to 700 cm3, smaller thanthe average 1350 cm3

volume of modernhumans, but larger thanthe 400 to 500 cm3 volumeof australopithecines.

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Culture developed in modern humans

Many hypotheses have been sug-gested to explain how modern humans,Homo sapiens, might have emerged.These hypotheses were formed afterstudying evidence from fossil bonesand teeth, and from studies of certaintypes of DNA. A description of themost popular hypothesis follows.

The fossil record indicates that thespecies H. sapiens appeared in Europe,Africa, the Middle East, and Asiaabout 100 000 to 500 000 years ago.The forms that are thought to pre-cede H. sapiens are placed by most sci-entists into one of two groups—H. antecessor or H. heidelbergensis (hiduhl berg EN sus). It is not yet clearwhich of these species represents the direct ancestor to Homo sapiens.More fossil evidence and additionalresearch into fossil DNA sequencesstill are needed. These early formshave skulls that resemble H. erectus orH. ergaster but have less prominentbrowridges, more bulging foreheads,and smaller teeth. Also, the braincasesare larger than H. erectus, with brainvolumes of 1000 to 1650 cm3, whichis within the modern human range. Awell-known Homo species was theNeandertals (nee AN dur tawlz), illus-trated in Figure 16.13.

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Figure 16.13Neandertals (Homo nean-derthalensis) were skilledhunters. They had manytools, including spears,scrapers, and knives.

Apply ConceptsHow similar are Neandertals and humans? Fossil evidencecan provide clues to similarities and differences betweenNeandertals and humans.

Solve the ProblemExamine the diagram of ahuman skull superimposed on aNeandertal skull. The cranialcapacities (brain size) of the twoskulls are provided.

Thinking Critically1. Measure How much larger

is a Neandertal brain than ahuman brain? Express thevalue as a percentage.

2. Interpret Scientific Illustrations Which skull has themore protruding jaw? A thicker browridge? Are a protrud-ing jaw and thick browridges more apelike or humanlikecharacteristics? Explain your judgment.

3. Identify What clues do fossils such as spear points andhand axes, shelters made of animal skins, and flowers andanimal horns at burial sites provide about the lifestyle ofNeandertals?

Brow-ridge

1600 cm3

1450 cm3

Neandertal

Modern human

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The Neandertals lived from about35 000 to 100 000 years ago inEurope, Asia, and the Middle East.Fossils reveal that Neandertals had thick bones and large faces withprominent noses. The brains ofNeandertals were at least as large asthose of modern humans.

The fossil records also indicate thatNeandertals lived in caves during theice ages of their time. In addition, thetools, figurines, flowers, pollen, andother evidence from excavation sites,such as burial grounds, suggest thatNeandertals may have had religiousviews and communicated throughspoken language.

What happened to Neandertals?Could Neandertals have evolved

into modern humans? No, the fossil

record shows that a more moderntype of H. sapiens spread throughoutEurope between 35 000 to 40 000years ago. This type of H. sapiens iscalled Cro-Magnon (kroh MAG nun).Cro-Magnons were identical tomodern humans in height, skullstructure, tooth structure, and brainsize. Paleoanthropologists suggestthat Cro-Magnons were toolmakersand artists, as shown in Figure 16.14.Cro-Magnons probably also used lan-guage, as their skulls contain a bulgethat corresponds to the area of thebrain that is involved in speech inmodern humans.

Did Neandertals evolve into Cro-Magnons? Current genetic and arch-aeological evidence indicates that thisis not the case. Current dates forhominid fossils suggest that modern

434 PRIMATE EVOLUTION(l)Science VU/Visuals Unlimited, (r)AKG Photo, London

Figure 16.14The dwelling sites of Cro-Magnons, full of cavepaintings, detailed stoneand bone artifacts, andtools, have been exca-vated in Europe.

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H. sapiens appeared in both SouthAfrica and the Middle East about 100 000 years ago, which was aboutthe same time the Neandertalsappeared. In addition, genetic evi-dence supports the idea of anAfrican origin of modern H. sapiens,perhaps as early as 200 000 yearsago. This idea suggests that theAfrican H. sapiens migrated toEurope and Asia.

Most fossil evidence supports theidea that Neandertals were mostlikely a sister species of H. sapiens,and not an ancestral branch of mod-ern humans. Look at Figure 16.15to see one possible evolutionary pathto modern humans.

Fossil evidence shows thathumans have not changed muchanatomically over the last 200 000years. Humans probably first estab-lished themselves in Africa, Europe,and Asia. Then evidence shows thatthey crossed either by sea or using aland bridge into North America.You can read more about the landbridge theory in the Connection toEarth Science at the end of the chap-ter. By about 10 000 to 8000 yearsago, Native Americans had builtpermanent settlements and weredomesticating animals and farming.

Understanding Main Ideas1. Describe the history of at least three major discov-

eries that led to our current understanding ofhominid evolution.

2. Why was the development of bipedalism a veryimportant event in the evolution of hominids?

3. What evidence supports the idea that H. habiliswas an ancestor of H. erectus?

4. Identify and describe the evidence that supportsthe idea that Neandertals were not the ancestorsof Cro-Magnon people.

Thinking Critically5. What kind of animal bones might you expect

to find at the site of Homo habilis remains ifH. habilis was a scavenger? A hunter?

6. Interpret Scientific Illustrations Draw a time line to show results of natural selection in the phylogeny or the evolutionary history of hominids. For more help, refer to InterpretScientific Illustrations in the Skill Handbook.

SKILL REVIEWSKILL REVIEW

16.2 HUMAN ANCESTRY 435ca.bdol.glencoe.com/self_check_quiz

Figure 16.15This diagram represents one possible pathway for theevolution of Homo sapiens. Not all scientists agree onthe evolutionary pathway.

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Before You BeginAustralopithecines are oneof the earliest hominids inthe fossil record. In manyways, their anatomy isintermediate between liv-ing apes and humans. Inthis lab, you’ll determinethe apelike and humanlikecharacteristics of an aus-tralopithecine skull, andcompare the skulls of aus-tralopithecines, gorillas,and modern humans. Thediagrams of skulls shownbelow are one-fourth nat-ural size. The heavy blacklines indicate the angle ofthe jaw.

Comparing Skulls ofThree Primates

ProblemHow do skulls of primates provide evidence for human evolution?

ObjectivesIn this BioLab, you will:■ Determine how paleoanthropologists study early human

ancestors.■ Compare and contrast the skulls of australopithecines,

gorillas, and modern humans.

Materialsmetric rulerprotractorcopy of skull diagrams

Skill HandbookIf you need help with this lab, refer to the Skill Handbook.

PREPARATIONPREPARATION

Gorilla1⁄4 natural size

Modern human1⁄4 natural size

Australopithecus1⁄4 natural size

Browridge

Sagittal crest

Browridge

436 PRIMATE EVOLUTION

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1. Face area in cm2

2. Brain area in cm2

3. Is brain area smalleror larger than face area?

4. Is brain area 3 times larger than face area?

5. Cranial capacity in cm3

6. Jaw angle

7. Does lower jaw stick outin front of nose?

8. Is sagittal crest present?

9. Is browridge present?

Gorilla Australopithecus Modern Human

Data Table

16.2 HUMAN ANCESTRY 437

1. Your teacher will provide copies of the skulls (1⁄4 natural size) of Australopithecus africanus, Gorilla gorilla, and Homo sapiens.

2. The rectangles drawn over the skulls represent the areas of the brain (upper rectangle) and face (lower rectangle). On each skull, determine and record the area of each rectangle (length � width).

3. Measure the diameters of the circles in each skull. Multiply these numbers by200 cm2. The result is the cranial capacity (brain volume) in cubic centimeters.

4. The two lines projected on the skulls are used to measure how far forwardthe jaw protrudes. Use a protractor to measure the acute angle formed bythe two lines.

5. Complete the data table.

PROCEDUREPROCEDURE

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

1. Compare and Contrast How would youdescribe the similarities and differences inface-to-brain area in the three primates?

2. Interpret Observations How do the cra-nial capacities compare among the threeskulls? How do the jaw angles compare?

3. Interpret Data Identify evidence of thechange in the species using anatomical similarities.

4. What are the possiblesources of error in your analysis?ERROR ANALYSIS

Use Models Obtain diagrams of primateskeletons to determine the similarities anddifferences using other parts of the skeletons.

Web Links To find out more aboutprimate evolution, visit ca.bdol.glencoe.com/primate_evolution

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438 PRIMATE EVOLUTION

The Land Bridge tothe New World

The Bering Land Bridge, or Beringia, was a strip of land that connected Asia and

North America. During the last Ice Age, theBering Land Bridge was dry land above sealevel. The ancestors of Native Americanswalked across this land to reach North America.

The 1500 km–wide piece of land known asthe Bering Land Bridge is located between theBering and Chukchi Seas and links northeasternSiberia and northwestern North America. Today,the land bridge is about 267 meters below theocean’s surface. However, during the last ice age,sea level was much lower than it is today. At thattime, this land bridge was above the water’s sur-face. Humans could have migrated from Asia toNorth America across this land bridge. Recentevidence indicates that such a human migrationprobably occurred about 12 000 years ago.

Dating the land bridge Anthropologistscompared two kinds of data to determine the11 000-year date for human migration across theBering Land Bridge. They used radiometric dat-ing methods on fossils and gathered informationon sea level changes over time. Both data revealthat the Bering Land Bridge was last above sealevel about 11 000 years ago.

Pollen reveals plant life Pollen found insediments dredged from the bottoms of theBering and Chukchi Seas indicates that the landbridge and the surrounding areas were tundraecosystems. Willows, birch, sedge tussocks, andspring flowers were the dominant plants of thearea, and caribou probably roamed over thefrozen soil.

The pollen studies also showed that the tem-perature at the time was warmer than it is inpresent-day Alaska. Scientists have used this

finding to propose that perhaps the ice age wasending. The glaciers would have melted in awarming climate and the sea level would haverisen, covering the land bridge with water.

A controversial idea Archaeologists haveunearthed what they believe to be human artifactsdating back to more than 12 000 years ago in sev-eral states. Some archaeologists believe that theseartifacts, such as stone spearheads, suggest thathumans occupied North America before the land bridge migration. Other archaeologists dis-agree, citing that no human fossils have beenfound, contamination of sites could have occurred,and that published reports confirming the datesand documenting the details of most of the siteshave not been completed.

Infer Study the map shown above. Suggest in ashort report another way that prehistoric humansmight have entered the New World.

To find out more about human origins, visitca.bdol.glencoe.com/earth_science

Modern coastline

Ancient coastline

Ice sheets 21 000 years ago

Ice sheets 12 000 years ago

Possible migration route

NORTHAMERICA

SOUTHAMERICA

Siberia

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Section 16.1Key Concepts■ Primates are primarily an arboreal group of

mammals. They have adaptations, such asbinocular vision, opposable thumbs, and flex-ible joints, that help them survive in trees.

■ There are two groups of primates: strepsir-rhines, such as lemurs; and haplorhines,which include tarsiers, monkeys, andhominoids.

■ There are two groups of monkeys: NewWorld monkeys and Old World monkeys.New World monkeys live in South Americaand Central America. Many New Worldmonkeys have a prehensile tail. Old Worldmonkeys are larger and do not have prehen-sile tails.

■ Hominoids are primates that include goril-las, chimpanzees, bonobos, gibbons, orang-utans, and humans.

■ Fossils indicate that primates appeared onEarth about 66 million years ago. Majortrends in primate evolution include anincreasing brain size and walking upright.

Vocabularyanthropoid (p. 424)opposable thumb

(p. 423)prehensile tail (p. 425)primate (p. 421)

PrimateAdaptation andEvolution

Vocabularyaustralopithecine

(p. 430)bipedal (p. 428)Cro-Magnon (p. 434)hominid (p. 428)hominoid (p. 428)Neandertal (p. 434)

HumanAncestry

STUDY GUIDESTUDY GUIDE

CHAPTER 16 ASSESSMENT 439(t)Mack Henry/Visuals Unlimited, (b)J. Beckette/D. Fannin/American Museum of Natural History

To help you review pri-mate evolution, use the OrganizationalStudy Fold on page 421.

Section 16.2Key Concepts■ The earliest hominids arose in Africa

approximately 5 million years ago. Australo-pithecine fossils indicate that these individu-als were bipedal, but also climbed trees.

■ The first hominid to be classified in thegenus Homo was discovered in Africa in1964 by Mary and Louis Leakey. The fos-sil was named Homo habilis or “handyhuman.” Homo habilis has been radio-metrically dated at between 1.5 and 2.5 million years old.

■ The appearance of stone tools in the fossilrecord coincided with the appearance ofthe genus Homo about 2 million years ago.

ca.bdol.glencoe.com/vocabulary_puzzlemaker

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Review the Chapter 16 vocabulary words listed inthe Study Guide on page 439. Determine if eachstatement is true or false. If false, replace theunderlined word with the correct vocabulary word.

1. New World monkeys have prehensile tails.2. Hominids include humans and the apes.3. Early hominids that lived in Africa and pos-

sessed both apelike and humanlike charac-teristics are called primates.

4. Bipedal organisms walk upright on two legs.

5. The first Homo sapiens were ________.A. Cro-Magnon peopleB. Homo erectusC. Australopithecus afarensisD. Neandertals

6. Which of the following pairs of terms ismost closely related?A. primate—squirrelB. arboreal—gorillaC. strepsirrhine—hominidD. Cro-Magnon—Homo sapiens

7. Primates native to the area indicated by themap below are ________.A. Old World monkeysB. New World monkeysC. apesD. strepsirrhines

8. The science of studying the fossils ofhumans is ________.A. paleoanthropologyB. geologyC. paleontologyD. anthropology

9. The earliest primates were most like _______.A. C.

B. D.

10. The study of the fossil Lucy helped scien-tists determine that ________.A. both primates and hominids have color

visionB. hominids are primates with opposable

thumbsC. hominids had large brains before they

walked uprightD. hominids walked upright before they had

large brains

11. Open Ended Suppose that you were told thata scientist found a 25 000-year-old arrowheadin Arizona. Would you be surprised? Why orwhy not?

12. Open Ended Why is it important for a paleo-anthropologist to know about all primates?

13. Open Ended Some scientists suggest thatNeandertals evolved into modern humans.What information should they gather tosupport their idea?

14. Almost everyyear the discovery of new fossils provides evi-dence for the evolution of human ancestors.Visit to find out aboutsome of the newest fossil discoveries. Whenand where were the fossils found? Write anessay to describe how the fossils add to ourunderstanding of primate evolution.

REAL WORLD BIOCHALLENGE

P A C I F I CO C E A N

AT L A N T I CO C E A N

440 CHAPTER 16 ASSESSMENT

ca.bdol.glencoe.com

ca.bdol.glencoe.com/chapter_test

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Multiple ChoiceUse the graph below to answer question 19.

19. According to the graph, which of the follow-ing is a true statement?

A. Hominid brains appear to increase in sizeas you go back in time.

B. Hominid brains appear to have remainedabout the same size for the last millionyears.

C. Hominid brains of the same species areall the same size.

D. Hominid brains have been increasing insize for at least three million years.

Read the following paragraph and use the illustration to answer questions 20 and 21.

Scientists have determined radiometric ages forvolcanic materials located near hominid fossils.A cross section showing layered volcanics andsediments containing the fossils is shown above.The location of each hominid fossil is indicatedwith an “X.” Ages of volcanic layers are given asnumbers in millions of years ago.

20. Which of the ages represents a maximum agefor the fossil hominids? In other words, whichis the oldest age that the fossils could be?A. 233 million years C. 2.33 million yearsB. 2.92 million years D. 3.18 million years

21. A minimum age for the fossils is indicatedby which age?A. 233 million years C. 2.33 million yearsB. 2.92 million years D. 3.18 million years

1600

1400

1200

1000

800

600

400

2000 0.5 1 1.5 2 2.5 3 3.5

Bra

in v

olu

me

(cm

3 )

Estimated age (in millions of years)

Brain Size Comparison

Range of living humans

Neandertals

Homo habilis

Australopithecus afarensis

Australopithecus africanus

15. Observe and Infer How could you tellfrom the position of the foramen magnumthat an animal walked upright? Explain.

16. Formulate Hypotheses How would you testthe idea that opposable thumbs are beneficialadaptations for arboreal mammals?

17. Compare and Contrast Compare and contrast strepsirrhines and haplorhines.

18. Hypothesize Explain why you think therecan be different interpretations for thepossible pathways of hominid evolution.

CHAPTER 16 ASSESSMENT 441

Surf

ace

2.33

2.92

3.18X

X

ca.bdol.glencoe.com/standardized_test

Constructed Response/Grid InRecord your answers on your answer document.

22. Open Ended Which characteristics are common to all primates? Include in your answer the majorfunction of each characteristic.

23. Open Ended Suppose you found a skull in an area where both Neandertals and Cro-Magnonslived. Explain the types of data you would use to determine which species the skull was from.

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