Our own species, Homo sapiens, belongs to the order that also

Transcription

1 32 3 Primates and Human Origins Section 32 3 Our own species, Homo sapiens, belongs to the order that also includes lemurs, monkeys, and apes. Carolus Linnaeus named our order Primates, which means first in Latin. What Is a Primate? Just what are primates first in? When the first primates appeared, there was little to distinguish them from other mammals besides an increased ability to use their eyes and front limbs together to perform certain tasks. As primates evolved, however, several other characteristics became distinctive. Primates share several important adaptations, many of which are extremely useful for a life spent mainly in trees. In general, primates have binocular vision, a welldeveloped cerebrum, relatively long fingers and toes, and arms that can rotate around their shoulder joints. The gibbon in Figure shows many of these characteristics. Fingers, Toes, and Shoulders Primates normally have five flexible fingers that can curl around objects. Most also have flexible toes. Flexible digits (fingers and toes) enable many primates to run along tree limbs and swing from branch to branch with ease. Primates arms are well adapted to climbing because they can rotate in broad circles around a strong shoulder joint. In most primates, the thumb and big toe can move against the other digits. The presence of this adaptation allows many primates to hold objects firmly in their hands or feet. Well-Developed Cerebrum The large and intricate cerebrum of primates including a well-developed cerebral cortex enables them to display more complex behaviors than many other mammals. For example, many primate species have elaborate social behaviors that include adoption of orphans and even warfare between rival primate troops. Key Concepts What characteristics do all primates share? What are the major evolutionary groups of primates? What is the current scientific thinking about hominid evolution? Vocabulary binocular vision prosimian anthropoid prehensile hominoid hominid bipedal opposable thumb Reading Strategy: Finding Main Ideas Before you read, draw a line down the center of a sheet of paper. On the left side, write down the main topics about primates and human origins. On the right side, note supporting details and examples. Figure A white-handed gibbon displays several primate characteristics as it swings from tree to tree. Like all primates, the gibbon has flexible fingers and toes and has arms that can rotate in broad circles around the shoulder joint. 1 FOCUS Objectives Identify the characteristics that all primates share Describe the major evolutionary groups of primates Explain the current scientific thinking about hominid evolution. Vocabulary Preview Help students differentiate between the words hominoid and hominid. First, say each word aloud. Then, write them on the board. Point out that the words differ only by their suffixes, -oid and -id. Explain that the suffix -oid comes from the Greek word eidos, meaning a form or shape. Then, explain that homomeans human being. Ask: If hominid is the name of the family that includes only humans, what does the word hominoid describe? (It describes the family of primates that look like humans. It includes humans as well as apes.) Reading Strategy While students read the section, they can write down the main topics on their sheet of paper. Remind them that they can find main ideas in boldface type, in topic sentences of paragraphs, and in headings and subheadings within the section. 2 INSTRUCT Print: SECTION RESOURCES Laboratory Manual A, Chapter 32 Lab Laboratory Manual B, Chapter 32 Lab Teaching Resources, Lesson Plan 32 3, Adapted Section Summary 32 3, Adapted Worksheets 32 3, Section Summary 32 3, Worksheets 32 3, Section Review 32 3, Enrichment Reading and Study Workbook A, Section 32 3 Adapted Reading and Study Workbook B, Section 32 3 Issues and Decision Making, Issues and Decisions, 15, 17 Technology: BioDetectives DVD, Mummies: Ties to the Past itext, Section 32 3 Transparencies Plus, Section 32 2 What Is a Primate? Applying Concepts Students probably take for granted their ability to pick up small objects. To help them sense the importance of flexible digits, challenge students to pick up small objects while wearing bulky mittens. Then, discuss how flexible digits not only help primates grasp tree branches, but also enable them to express additional behaviors, such as using tools, eating certain foods, and grooming. Mammals 833

2 32 3 (continued) Objective Students will be able to conclude how binocular vision is useful. Skills Focus Using Tables and Graphs, Drawing Conclusions Material sheet of paper Time 10 minutes Safety Make sure students have enough room to move so they don t trip over things while catching. Strategy As an alternate activity, have students hold a pipe cleaner in one hand and a drinking straw in the other. They should extend their arms in front of them and try to insert the pipe cleaner into the straw. They should first do this with both eyes open and then repeat the procedure with one eye closed. Most students will find the procedure easier when they have both eyes open. Expected Outcome Students will find the ball more difficult to catch when they have one eye closed. Analyze and Conclude 1. Graphs should show that more students are able to catch the ball with both eyes open. The combination of two perspectives with both eyes open provides depth perception. 2. Many primates move by swinging through trees. The ability to judge distances enables them to grasp branches quickly. Is binocular vision useful? Material paper crumpled into a ball Procedure 1. Throw the paper ball to your partner, who should try to catch the ball with one hand. Record whether your partner caught the ball. 2. Now have your partner close one eye. Repeat step 1. Analyze and Conclude 1. Using Tables and Graphs Exchange results with other groups. Make a bar graph for the class data comparing the results with both eyes open and one eye shut. 2. Drawing Conclusions How is binocular vision useful to primates? Lorises and bush babies Lemurs Tarsiers Binocular Vision Many primates have a flat face, so both eyes face forward with overlapping fields of view. This facial structure gives primates excellent binocular vision. Binocular vision is the ability to merge visual images from both eyes, thereby providing depth perception and a three-dimensional view of the world. This is a handy adaptation for judging the locations of tree branches, from which many primates swing. Evolution of Primates Humans and other primates evolved from a common ancestor that lived more than 65 million years ago. Early in their history, primates split into several groups. Primates that evolved from two of the earliest branches look very little like typical monkeys and are called prosimians (proh-sim-eeunz). Members of the more familiar primate group that includes monkeys, apes, and humans are called anthropoids (AN-thruh-poydz). Refer to Figure as you read about the phylogenetic relationships among these groups. Prosimians With few exceptions, prosimians alive today are small, nocturnal primates with large eyes that are adapted to seeing in the dark. Many have doglike snouts. Living prosimians include the bush babies of Africa, the lemurs of Madagascar, and the lorises and tarsiers of Asia. What is a prosimian? Hominoids New World Old World monkeys monkeys Gibbons Orangutans Gorillas Chimpanzees Humans Prosimians Anthropoids Evolution of Primates Classifying Give student groups pictures of several different primates. Challenge groups to classify the primate in each picture as a prosimian or an anthropoid. Students should list characteristics of the primate that caused them to classify it as they did. FACTS AND FIGURES Primate ancestor Prosimians live here The more familiar primate characteristics are less obvious in many prosimians. Some prosimians have long snouts, and their sense of smell is still very important to their survival. Others have very Figure The diagram illustrates the phylogeny of modern primates. The two main groups of primates are prosimians and anthropoids. large eyes, probably an adaptation to nocturnal life. Prosimians are found only in the tropical forests of Africa, Southeast Asia, Madagascar, and the West Indies. Many prosimians are in danger of extinction because of habitat destruction. 834 Chapter 32

3 Anthropoids Humans, apes, and most monkeys belong to a group called anthropoids, which means humanlike primates. This group split very early in its evolutionary history into two major branches. These branches became separated from each other as drifting continents moved apart. One branch, found today in Central and South America, is called the New World monkeys. (After Columbus s voyage to America, Europeans began to use the term New World to refer to North and South America.) New World monkeys, which include squirrel monkeys and spider monkeys, live almost entirely in trees. These monkeys have long, flexible arms that enable them to swing from branch to branch. New World monkeys also have a long, prehensile tail. A prehensile tail is a tail that can coil tightly enough around a branch to serve as a fifth hand. The other anthropoid group, which evolved in Africa and Asia, includes the Old World monkeys and great apes. Old World monkeys, such as langurs and macaques (muh-kahks), spend time in trees but lack prehensile tails. Great apes, also called hominoids, include gibbons, orangutans, gorillas, chimpanzees, and humans. Recent molecular studies confirm that chimpanzees are humans closest relatives among the great apes. Humans and chimps share an astonishing 98 percent of their DNA! Hominid Evolution Between 6 and 7 million years ago, the hominoid line gave rise to a branch that ultimately led to the ancestors and closest relatives of modern humans. The hominid family, which includes modern humans, displayed several distinct evolutionary trends. Fossil evidence shows that as hominids evolved over millions of years, they became able to walk upright and developed thumbs adapted for grasping. They also developed large brains. The skull, neck, spinal column, hipbones, and leg bones of early hominid species changed shape in ways that enabled later species to walk upright. Figure shows some ways in which the skeletons of modern humans differ from those of gorillas. The evolution of this bipedal, or two-foot, locomotion was very important, because it freed both hands to use tools. Meanwhile, the hominid hand evolved an opposable thumb that enabled grasping objects and using tools. Modern Human Modern Human Skull atop S-shaped spine Spinal cord exits at bottom of skull Arms shorter than legs; hands do not touch ground during walking Pelvis is bowlshaped Thigh bones angled inward, directly below body Modern Gorilla Comparing Human and Gorilla Skeletons Modern Gorilla Skull atop C-shaped spine Spinal cord exits near back of skull Arms longer than legs; hands touch ground during walking Pelvis is long and narrow Thigh bones angled away from pelvis Figure Modern hominids walk upright on two legs; gorillas use all four limbs. Comparing and Contrasting According to the chart and illustration, what are the other differences between humans and gorillas? Make Connections Earth Science On a map, show students how the eastern coast of South America fits into the western coast of Africa. Explain that primates first evolved when these two continents were connected. As the continents drifted apart, primate species were separated. Ask: How do you think New World and Old World monkeys became different? (As the two groups became separated, they responded to different selection pressures climate, food sources, environment and evolved somewhat differently.) Discuss the kinds of environmental changes that helped make the Old World monkeys different from New World monkeys. (Old World monkeys adapted to an environment with fewer trees. They lost their prehensile tail, tend to sit upright, and have an opposable thumb. Most New World monkeys remain completely adapted to living in trees. Nearly all have a prehensile tail, but most lack opposable thumbs.) Hominid Evolution Use Visuals Figure Explain that the S-shaped spine of the human skeleton places the center of gravity directly over the pelvis. Ask: Why doesn t the gorilla usually walk on two legs? (It needs its arms to balance its body because the body leans forward.) Have students compare the size of the human and the gorilla skulls. UNIVERSAL ACCESS Less Proficient Readers To help students organize the main ideas and reinforce the meanings of Vocabulary terms, have them create a concept map to show the relationships and characteristics of prosimians, anthropoids, hominoids, and hominids. Make sure students know the difference between hominoids and hominids. Also point out how anthropoid differs from arthropod. Advanced Learners Students who would like an extra challenge can read Mary Leakey s autobiography entitled Disclosing the Past. Students who have read the book can discuss what they think about Mary Leakey s life and how they felt after reading her story. Or, you might have these students work together to prepare a class presentation about Mary Leakey s life. Answers to... Most prosimians are small, nocturnal primates with large eyes. Figure Spine shape, site where spinal cord exits skull, length of arms, position of hands during walking, shape of pelvis, angle of thigh bones Mammals 835

4 32 3 (continued) Address Misconceptions Some students might think that humans evolved directly from modern apes or chimpanzees. Explain that humans and apes shared a common ancestor, but humans did not directly evolve from modern apes. You can illustrate this idea by drawing a phylogenetic tree showing apes and humans diverging from a common ancestor. Discuss how theories about human ancestors have changed over time. Explain that DNA evidence, used in conjunction with fossil evidence, is also changing the way human history is interpreted. Point out the different scientific disciplines that have been involved in the study of human ancestry. Make sure students know the specialty of each scientist and understand what that specialty entails. Discuss how the knowledge of these scientists has contributed to the study of human origins. Remind students that there is no single correct answer. Challenge them to put themselves into Mary Leakey s shoes. Give them as much background information about Mary Leakey and her work as possible. As they write the journal entry, students should feel and convey the excitement that Mary Leakey felt upon making her discovery. Remind students that the journal entry should be written in the first person. Encourage them to imagine and develop any details about the day and the discovery. Figure Between 3.8 and 3.6 million years ago, members of a species of Australopithecus made these footprints at Laetoli in Tanzania. The footprints show that hominids walked upright millions of years ago. Human-Fossil Seekers The study of human origins is an exciting search for our past. To piece together this complicated story requires the skills of many scientists Georges Cuvier Cuvier, a French zoologist, rejects the idea of evolution based on a lack of evidence in the fossil record. He is noted for saying Fossil man does not exist! He believed species were static and unchanging. Hominids also displayed a remarkable increase in brain size. Chimpanzees, our closest living relatives among the apes, have a brain size of 280 to 450 cubic centimeters. The brain of Homo sapiens, on the other hand, ranges in size from 1200 to 1600 cubic centimeters! Most of the difference in brain size results from an enormously expanded cerebrum the thinking area of the brain. Early Hominids Paleontologists have unearthed a treasure trove of hominid species. At present, most paleontologists agree that the hominid fossil record includes at least these genera Ardipithecus, Australopithecus, Paranthropus, Kenyanthropus, and Homo and as many as 20 separate species. This diverse group of hominid fossils covers roughly 6 million years. All these species are relatives of modern humans, but not all of them are human ancestors. To understand that distinction, think of your family. Your relatives may include aunts, uncles, cousins, parents, grandparents, and great-grandparents. Of these, only your parents, grandparents, and great-grandparents are your ancestors. Almost a third of all known hominid species have been discovered in the last 20 years. This shows how rapidly knowledge of hominid fossils is growing. It also explains why hominid evolution is both fascinating and confusing. What once looked like a simple human family tree now looks more like a dense, branching shrub. Many questions remain about how fossil hominids are related to one another and to humans. Let s examine a few of the most important discoveries Edouard Lartet Henry Christy French geologist Lartet and English banker Christy unearth several ancient human skeletons in a rock shelter called Cro- Magnon in France. These hominid fossils are the first to be classified as Homo sapiens HISTORY OF SCIENCE 1886 Marcel de Puydt Max Lohest De Puydt and Lohest describe two Neanderthal skeletons found in a cave in Belgium. Their detailed description of the skeletons shows that Neanderthals were an extinct human form, not an abnormal form of modern human. Edouard Lartet Founder of Paleontology Although Edouard Lartet was trained as a lawyer, his discovery of fossil remains at the age of 33 changed his life forever. From then on, he devoted his time to excavating caves in France. He found many examples of early tools made from bone, flint, and antlers. Many caves had colorful drawings of animals. In 1863, the English banker Henry Christy teamed up with Lartet, giving him funding to support his research. Working together, they found a mammoth bone with an image of an extinct animal carved in it. Their discoveries showed that Ice Age mammals lived at the same time as ancient humans. This idea was under great debate at the time. They also showed that the Stone Age was made up of different phases of human culture. 836 Chapter 32

5 Australopithecus One early group of hominids, members of the genus Australopithecus, lived from about 4 million to a million years ago. These hominids were bipedal apes that spent at least some time in trees. The structure of their teeth suggests a diet rich in fruit. Some Australopithecus species seem to have been human ancestors, while others formed separate branches off the main hominid line. The best known species is Australopithecus afarensis described from a remarkably complete female skeleton, nicknamed Lucy, who stood only about 1 meter tall. The humanlike footprints shown in Figure 32 17, which are between 3.8 and 3.6 million years old, were probably made by members of the same species as Lucy. Since Australopithecus fossils have small brains, the Laetoli footprints show that hominids walked bipedally long before large brains evolved. Paranthropus Three later species, which grew to the size of well-fed football linebackers, were originally placed in the genus Australopithecus. However, they are now usually placed in their own genus, Paranthropus. The known Paranthropus species had huge, grinding back teeth. Their diets probably included coarse and fibrous plant foods like those eaten by modern gorillas. Most paleontologists now place Paranthropus on a separate, dead-end branch of our family tree. What are the characteristics of Paranthropus? Discovery School Video To find out more about human history, view track 6 Mummies: Ties to the Past on the BioDetectives DVD. Discovery School DVD Encourage students to view track 6 Mummies: Ties to the Past on the BioDetectives DVD. Using Models Students will benefit from constructing a timeline that marks the time period during which each hominid species lived. Students should realize that some hominid species lived during the same time. Help students put into perspective the large expanse of time over which these hominid ancestors lived and died Raymond Dart Dart, an Australian anatomist, finds an early hominid fossil a nearly complete skull of a child in South Africa. This specimen was placed in a new genus called Australopithecus Donald Johanson An American paleontologist and his team find 40 percent of a skeleton of Australopithecus, which they call Lucy, in the Afar region of Ethiopia. The skeleton is about 3.2 million years old Mary Leakey Leakey, a British anthropologist, discovers a set of 3.6 million-year-old fossil hominid footprints at Laetoli in Tanzania. The footprints provide evidence that early hominids walked erect on two legs. You have found Mary Leakey s journal and noticed that the entry for her discovery of the footprints at Laetoli is missing. Write an entry for the journal as she would have, describing the events of the day and her initial reaction to the find Douglas Wallace Wallace and fellow geneticists create a family tree of human evolution based on their studies of mitochondrial DNA, which is passed only from mother to child HISTORY OF SCIENCE The Leakey family of anthropologists Mary Nicol Leakey was born in London in 1913, but she spent much of her life moving around Europe with her family. During her early twenties, she began working at archaeological sites, where she learned to be methodical and careful. She also became known for her abilities in illustration. In 1936, she married the anthropologist Louis Leakey, whom she met at a dinner party after a lecture. She went with him to Africa, where he was working to prove that humans originated there rather than in Asia, as was popularly thought at the time. She spent over 20 years excavating sites in the Serengeti Plains in northern Tanzania. She and her husband collected many tools and fossilized skulls of early hominids. Her greatest find, the fossilized footprints at Laetoli, came after her husband s death. Answer to... Paranthropus species were very large and had huge, grinding back teeth. Mammals 837

6 32 3 (continued) Use Visuals Figure Point out that the skulls are arranged in order according to the age of the fossil species, with the oldest, Sahelanthropus tchadensis, at the top, and the most recent, Homo erectus, at the bottom. Have students compare and contrast the structure of the skulls. Ask: In what ways are the skulls of Sahelanthropus tchadensis and Homo erectus similar? In what ways are they different? (Both have eye sockets facing forward, indicating that they have binocular vision, as do all primates. Both have relatively large brain cases. However, H. erectus has the larger brain. S. tchadensis has a flat face.) Evaluating and Revising Deciphering early hominid evolution provides a very good example of how the scientific method works in real-life scientific study. Point out how the discoveries of new fossils have changed original hypotheses formed by paleontologists. Also point out how those new discoveries have led to even more questions. Work with students to put recent changes in thinking about hominid evolution into the context of the scientific method. Discuss the questions that paleontologists are asking, as well as their hypotheses. Ask: How have paleontologists changed their hypotheses to reflect recent discoveries? (Instead of hominid evolution following a simple, straightline transformation of one species into another, hominid evolution followed a series of complex adaptive radiations to produce a large number of species.) Sahelanthropus tchadensis Kenyanthropus platyops Homo erectus Figure Paleontologists interpretations of hominid evolution are based on the study of fossils such as these skulls. Sahelanthropus may be the earliest known hominid. Observing Which of these skulls most closely resembles the skull of a modern human? Recent Hominid Discoveries Early in 2001, a team led by paleontologist Meave Leakey announced that they had uncovered a skull in Kenya. Its ear structures resembled those of chimpanzees, and its brain was rather small. Yet some of its facial features resembled those of fossils usually placed in the genus Homo. Paleontologists put this skull in a new genus, Kenyanthropus. Kenyanthropus is shown in the middle in Figure Evidence indicates that this species existed at the same time as A. afarensis. Then, during the summer of 2002, paleontologists working in the desert in north-central Africa announced the discovery of an even more startling skull. This fossil skull, tentatively called Sahelanthropus, is nearly 7 million years old. If scientists agree that Sahelanthropus is indeed a hominid, it would be a million years older than any hominid previously known. Sahelanthropus had a brain about the size of a modern chimp, yet its short, flat face is more like that of a human. In fact, this skull seems more humanlike in certain ways than Lucy (A. afarensis), who lived several million years later. While most hominid fossils have been discovered in eastern Africa, Sahelanthropus was discovered much farther to the west. This suggests that there may be many more fossil hominids to be found in widely separated parts of Africa. What is Kenyanthropus platyops? Rethinking Early Hominid Evolution Together with other recent fossil finds, the discovery of Kenyanthropus and Sahelanthropus has dramatically changed the way paleontologists think about hominid evolution. Researchers once thought that human evolution took place in relatively simple steps in which hominid species, over time, became gradually more humanlike. It is now clear that hominid evolution did not proceed by the simple, straight-line transformation of one species into another. Rather, like the evolution of other mammalian groups, a series of complex adaptive radiations produced a large number of species whose relationships are difficult to determine. Which hominids are true human ancestors? Which are just relatives? And how are all those species related to one another and to modern humans? At present, no one can answer these questions. So what is known about hominid evolution? As shown in Figure 32 19, the hominid fossil record now dates back nearly 7 million years, close to the time that DNA studies suggest for the split between hominids and the ancestors of modern chimpanzees. In addition, there are many known fossil hominid species, several of which display a confusing mix of primitive and modern traits. It will probably take many years of work to more fully understand this fascinating and complex story. FACTS AND FIGURES Changing African climate and evolution The climate of East Africa began changing about 10 million years ago. The air became drier, and forests gave way to grasslands. Many primates remained in the forests. But as the environment became more diverse, different primates evolved to establish new niches. These primates had characteristics that enabled them to live more successfully in open grassland. Their diet changed from being completely herbivorous to omnivorous. They began walking upright on two feet. Bipedalism enabled primates to see over the tops of grass and bushes. It enabled them to carry food or offspring in their arms. It also kept them cooler, because they received less of the sun s direct rays and could catch cool breezes above the ground. The gradual loss of body hair also helped to keep them cooler. 838 Chapter 32

7 Sahelanthropus tchadensis (?) Orrorin tungenensis The Road to Modern Humans Australopithecus bahrelghazali Au. anamensis Kenyanthropus platyops Au. afarensis Ardipithecus ramidus Millions of Years Ago The hominids that have been mentioned so far, such as Paranthropus and Australopithecus, all lived millions of years before modern humans. When did our species, Homo sapiens, appear? As you can see in Figure 32 19, other species in our genus existed before H. sapiens, and at least two other species in the genus Homo existed at the same time as early humans. As is the case with earlier hominid fossils, paleontologists still do not completely understand the history and relationships of species within our own genus. The Genus Homo About 2.5 million years ago, a new kind of hominid appeared. Its fossils show that it resembled modern humans enough to be classified in the genus Homo. Because these fossils were found with tools made of stone and bone, researchers called the species Homo habilis (HAB-ih-lus), which means handy man. Homo habilis was the first of several species in our genus to arise in Africa. About 2 million years ago, a species larger than H. habilis appeared. It had a bigger brain and downward-facing nostrils that resembled those of modern humans. Today, most researchers call the African fossils of this species Homo ergaster. At some point, one or more species in the genus Homo began migrating out of Africa through what is now the Middle East. That species may have been H. ergaster or a closely related species named Homo erectus. Homo sapiens H. neanderthalensis H. heidelbergensis H. antecessor H. erectus H. ergaster H. habilis Au. rudolfensis Au. garhi Au. africanus Paranthropus robustus P. aethiopicus P. boisei Figure The diagram shows fossil hominids and the time ranges during which they may have existed. The time ranges are likely to change as paleontologists gather new data. The question mark after Sahelanthropus tchadensis indicates that scientists are not yet certain that this species is a hominid. Paleontologists do not yet have enough information to know how hominid species are related. It is now clear that hominid evolution did not proceed by the simple, straight-line transformation of one species into another. Current hypotheses about early stages of human evolution recognize the incompleteness of the data. The Road to Modern Humans Address Misconceptions Some students might have the misconception that human ancestors were dumb cave men. Address this by explaining that a large part of human evolution was developing the ability to learn and to teach. Point out that our knowledge base is large because it continues to be built on what is already known. This base of knowledge will continue to grow as new discoveries are made. If you wish, you can illustrate this concept with interlocking building blocks. Starting at the base with blocks representing simple tools made from sticks, bones, and stones, students can build a wall or other structure. Each block they add to the structure should represent some innovation or discovery that expands the knowledge base of humans. Answers to... Kenyanthropus platyops is the species name given to a fossil skull discovered in Kenya by Meave Leakey s team. The skull has a flat face. It has some characteristics of chimpanzees and some characteristics of the genus Homo. Figure Homo erectus Mammals 839

8 32 3 (continued) Use Visuals Figure Ask: At which sites did hominids live more than 2 million years ago? (Olduvai, Kanapoi, and Hadar) How many times might hominids have left Africa for the Middle East? (Four times) When? (2.0 to 1.5 million years ago, 1.0 to 0.5 million years ago, 0.5 to 0.1 million years ago, and less than 0.1 million years ago) When were hominids first in what is now Beijing? (1.0 to 0.5 million years ago) How have scientists learned the history of human ancestors? (By studying the fossil record and testing human DNA) Atapuerca Hadar Turkana Kanapoi Olduvai Dmanisi Ubeidiya Indian Ocean Site of Hominid Fossil Direction of Migration Riwat Millions of Years Ago Less than to to to to 1.5 More than 2.0 Longgupo Beijing Java Making Judgments Challenge students to make a list of objects that they would include in a time capsule. Students should choose no more than ten items and give reasons for each choice. They should choose items with the idea that the time capsule will be opened 100,000 years from now. These items should give anthropologists information about what students lives were like. Applying Concepts Challenge students to make comparisons of their lifestyle to that of ancient humans. Discuss how different our lives are now, as well as how some aspects of our lives might be similar. Encourage students to make predictions about what life will be like in the future. You could have students write an essay describing their thoughts and predictions. Figure Data show that relatives and ancestors of modern humans left Africa several different times. But when did early hominids leave Africa, and how far did they travel? By comparing the mitochondrial DNA of human populations around the world and by continuing to study the fossil record, scientists hope to improve our understanding of the complex history of Homo sapiens. NSTA For: Links on human evolution Visit: Web Code: cbn-9323 Out of Africa But Who and When? Researchers agree that our genus originated in Africa. But many questions remain. When did hominids first leave Africa? Did more than one species make the trip? Which of those species were human ancestors and which were merely relatives? Fossil data and molecular evidence suggest that hominids left Africa in several waves as shown in Figure By a million years ago, migrants from Africa had crossed Asia and reached China and Java, and populations of H. erectus were living in several places across Asia. Many researchers have hypothesized that H. erectus was the first of our genus to leave Africa. Two recently discovered fossil skulls may offer additional evidence that H. erectus did leave Africa and migrate long distances. The skulls, which strongly resemble African H. erectus fossils and are about 1.75 million years old, were discovered in the country of Georgia, which is north of Turkey and far from Africa. However, other evidence makes the situation less clear. Another 1.75-million-year-old skull found in Georgia resembles 1.9 million-year-old Homo habilis skulls from Kenya. Does this skull indicate that H. habilis left Africa before H. erectus? The scientific jury is still evaluating the evidence. Paleontologists are also unsure exactly where and when Homo sapiens arose. One hypothesis, the multi-regional model, suggests that modern humans evolved independently in several parts of the world from widely separated populations of H. erectus. Another hypothesis, the out-of-africa model, proposes that modern humans evolved in Africa between 200,000 and 150,000 years ago, migrated out to colonize the world, and replaced the descendants of earlier hominid species. Scientific debate and the search for more data continue. NSTA Download a worksheet on human evolution for students to complete, and find additional teacher support from NSTA SciLinks. 840 Chapter 32

9 Modern Homo sapiens The story of modern humans over the past 500,000 years involves two main groups. The earliest of these species is now called Homo neanderthalensis, named after the Neander Valley in Germany where their remains were first found. Neanderthals, as they are commonly called, flourished from Europe through western Asia between about 200,000 and 30,000 years ago. Evidence from Neanderthal sites in Europe and the Middle East suggests that they not only made stone tools but also lived in organized social groups. The other group is anatomically modern Homo sapiens in other words, people whose skeletons look like those of modern humans. These H. sapiens, who probably arose in Africa, appeared in the Middle East around 100,000 years ago. They joined Neanderthals who had been living in that region for at least 100,000 years. As far as anyone can tell, Neanderthals and Homo sapiens lived side by side in what is now Israel, Lebanon, Syria, and Turkey for around 50,000 years, using similar tools and living in remarkably similar ways. That situation may have changed dramatically around 50,000 40,000 years ago. According to one hypothesis, that s when some populations of H. sapiens seem to have fundamentally changed their way of life. They used new technology to make more sophisticated stone blades, and made elaborately worked tools from bones and antlers. They produced spectacular cave paintings, such as the one in Figure These Homo sapiens buried their dead with elaborate rituals. In other words, these people began to behave like modern humans. About 40,000 years ago, one such group, known as Cro-Magnons (kroh- MAG-nunz), appeared in Europe. By 30,000 years ago, Neanderthals had disappeared from Europe and from the Middle East as well. How and why they disappeared is not yet known. But since that time, our species has been Earth s only hominid Section Assessment Figure This ancient cave painting from France shows the remarkable artistic abilities of Cro-Magnons. Inferring How might these painted images be related to the way in which these early humans lived? Modern Homo sapiens Formulating Hypotheses Challenge students to develop a hypothesis to explain what happened to Homo neanderthalensis. Have students describe the type of fossilized evidence they must find that would support their hypothesis. Also have them describe what type of fossilized evidence would refute their hypothesis. 3 ASSESS Evaluate Understanding Have students make a family tree that shows how the primate groups (prosimians, anthropoids, hominoids, and hominids) evolved from a common ancestor. Instruct students to list the characteristics of each group. Reteach Have students copy the Vocabulary words from this section. For each word, students should write its meaning in their own words. For those words that describe primate groups, students should include the characteristics of primates belonging to that group. 1. Key Concept List five anatomical characteristics that most primates share. 2. Key Concept Describe the major primate groups and explain how they are related phylogenetically. 3. Key Concept Explain the way that paleontologists currently view hominid evolution. 4. Compare and contrast hominids and other hominoids. How are they similar? Different? 5. Critical Thinking Applying Concepts How did the separation of the continents contribute to the development of New World and Old World monkeys? Explanatory Paragraph Write a paragraph explaining how the structure of primates fingers, toes, and shoulders are adaptations that help with survival. Hint: To prepare to write, make a table that describes the structures in the left column and then lists the advantages of those structures in the right column. In their paragraphs, students should explain that the structure of primates fingers, toes, and shoulders enables them to run along tree limbs and swing from branches. This behavior enables primates to find food and escape predators Section Assessment 1. Binocular vision, well-developed cerebrum, relatively long fingers and toes, and arms that can rotate around their shoulder joints 2. Two major groups descended from a common primate ancestor. Prosimians: small, nocturnal primates; anthropoids: humanlike primates, split into two groups: (1) New World monkeys and (2) Old World monkeys and hominoids. 3. A series of complex adaptive radiations produced a large number of species whose relationships are difficult to determine. 4. Both groups are similar in that they are anthropoids. For differences, see the chart in Figure 32 16, page The two groups responded to different environmental pressures and evolved differently. If your class subscribes to the itext, use it to review the Key Concepts in Section Answer to... Figure The paintings might show how these early humans hunted large animals. Mammals 841