WHAT ARE PRIMATES?
¨PERSPECTIVE Footprints at Laetoli
The Human Lineage
The following content objectives are presented in Chapter 19:
¨ Primates are difficult to characterize as an order because they lack strong specializations found in most other mammalian orders.
¨ Primates are divided into two suborders: the prosimians, which include lemurs and tarsiers, and the anthropoids, which include monkeys, apes, and humans.
¨ The hominids include present-day humans and their extinct ancestors.
¨ Human evolution is very complex and in a constant state of flux owing to new fossil and scientific discoveries.
¨ The most famous of all fossil humans are the Neanderthals, which were succeeded by the Cro-Magnons, about 30,000 years ago.
To exhibit mastery of this chapter, students should be able to demonstrate comprehension of the following:
¨ the characteristics and evolution of the primate groups
¨ the characteristics of australopithecines and their place in human evolution
¨ the complexity of human evolution reconstruction
¨ the evolutionary history of the genus Homo, including Neanderthals and Cro-Magnons
¨ the migration of humans on the Earth
1. The primates evolved during the Paleocene. Several trends help characterize primates 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.
Figure 19.1 Primates
Table 19.1 Classification of the Primates
Enrichment Topic 1. Changing Tectonics, Climate, and Human Evolution
East Africa is one of the most changed landscapes in recent geological history. Tectonic movements and climate changes influenced the area during the time that humans were evolving. As the Himalayans were rising, the moist air was sucked from the Indian Ocean to produce the Southeast Asian monsoons. This deflected moisture away from Africa, drying out the African continent. The distinct climatic split between Asia and Africa corresponds to the split between Asian and African apes! The effect of the formation of the African Rift Valley has also had an effect on evolution. The eastern rift shoulder acted as an impediment to moisture, causing the area to dry out even further. The topography also changed from a flat region to a more mountainous region. It is proposed that this change may have caused the evolution of bipedalism, sometime after 6 million years ago. The effects of tectonism on human evolution are not restricted to Africa. As the Isthmus of Panama formed, the water exchange between the Pacific and Atlantic oceans cased. This, in turn, strengthened the Gulf Stream by pumping more warm water northward, which in turn provided the moisture for the growth of the Pleistocene ice sheets. How did the drying out of the African continent affect evolution? Rick Potts hypothesized that during dry periods, hominid brains may have evolved as a means of dealing with the variable environment. Larger jaws may also have developed through natural selection so that the early hominids could eat just about anything.
Maslin, Trauth, and Christensen, “A Changing Climate for Human Evolution,” Geotimes, Sept. 2005, v.50 n.9 p.18-22.
2. 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 hominoids, which are humans and their extinct ancestors.
Figure 19.2 Eocene Prosimian
Figure 19.3 Aegyptopithecus zeuxis
Figure 19.4 Proconsul
Figure 19.5 Comparison of Gorilla and Human Locomotion and Hominid Brian Size
Enrichment Topic 2. The Last Common Ape Ancestor
A discovery of Pierolapithecus catalaunicus has scientists speculating that it may be the last common ancestor of the great ape family and humans. Found in Spain, the fragments recovered indicated that the organism stood approximately four feet tall and weighed 66-77 pounds. Nicknamed Pau, the fossil revealed that the organism had a broad, sloping face and a wide rib cage, plus a flexible wrist for climbing. The fingers were more monkey-like than apelike, however. Pau may support the hypothesis that early ancestors of humans evolved in Eurasia, and migrated back to Africa. “New Limb on Family Tree,” Discover, Feb. 2005, v.28 n.2 p.9.
3. The oldest known hominoid is Sahelanthropus tchadensis, dated at nearly 7 million years. It was followed by Orrorin tugenensis at 6 million years, then two subspecies of Aradipitherus at 5.8 and 4.4 million years respectively. The early hominids were succeeded by the australopithecines, a fully bipedal group that evolved in Africa 4.2 million years ago. Currently, five australopithecine species are known: Australopithecus anamensis, A. afarensis, A. africanus, A. robustus, and A. boisei.
Figure 19.6 The Stratigraphic Record of Hominids
Figure 19.7 Sahelanthropus tchadensis
Figure 19.8 Skeleton of Lucy (Australopithecus afarensis)
Figure 19.9 African Pliocene Landscape
Figure 19.10 Australopithecus africanus
Figure 19.11 Australopithecus robustus
4. The Homo 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.
Figure 19.12 Homo habilis
Enrichment Topic 3. Europe’s Oldest Hominid
In 2008, the oldest fossil hominid of Europe was found in the form of a jawbone in Spain. Assigned to the species Homo antecessor, the fossil is approximately 1.2 million years old. The new find suggests that early humans arrived in Europe sooner that previously acknowledged. Wright, “Europe’s Oldest Hominid Unearthed,” Discover, January 2009, p.60.
5. Homo erectus evolved about 1.8 million years ago and was the first hominid to migrate out of Africa. Between 1.8 and 1 million years ago, H. erectus had spread to Europe, India, China, and Indonesia. H. erectus used fire, made tools, and lived in caves.
Figure 19.13 Homo erectus
Figure 19.14 European Pleistocene Landscape with Homo erectus
Enrichment Topic 4. The Clubbing Wars?
Although Homo erectus appears to be related to the modern human lineage, researchers were long puzzled over the very unique qualities of the skull. The researchers hypothesized that the thickening of skull areas was a response to behaviors within the species.
The skullcap and other features of the skull and jaws indicate that the species was adapted for defense against trauma. The researchers hypothesized that the patterns witnessed in H. erectus’ skull evolved in response to interpersonal violence. Even today, some groups practice intergroup warfare. Why would these features be lacking in modern humans, if H. erectus represented one of our ancestors? The researchers hypothesized that these features may have disappeared because cranial bone may have become thinner, just to reduce the weight of the skull. Boaz and Ciochon, “Headstrong Hominids,” Natural History, Feb. 2004, v.113. n.1 p.21-34.
6. Sometime between 200,000 and 100,000 years ago, Homo sapiens evolved from Homo erectus.
7. Neanderthals were not much different from present-day humans, only more robust and with different shaped skulls. They made specialized tools and weapons, apparently took care of their injured, and buried their dead.
Figure 19.15 Neanderthal Skull
Figure 19.16 Pleistocene Cave Setting with Neanderthals
Enrichment Topic 5. Neanderthals and Modern Humans
Researchers working at two sites in Gibralter discovered that Neanderthals exploited the food resources of their coastal environment, and ate seals, dolphins, and fish. They also cooked mussels. Other studies point to Neanderthals as gifted toolmakers. When Neanderthal and Cro-Magnon tools were recreated, the Neanderthal tools lasted longer, and wasted less rock when produced. Although Neanderthal brains developed differently from modern humans, new discoveries revealed that Neanderthal babies were also born with brains as large as modern humans. Although the Neanderthals were surprising more similar to modern humans that previously acknowledged, computational biologist Richard Green published the first sequence of 38,000 year-old Neathderthal mitochondrial DNA. The sequence indicated that the split between modern humans and Neanderthals occurred about 660,000 years ago. No genetic evidence indicates that Neanderthals and modern humans ever interbred. Ruvinsky, “They’re Just Like Us,” Discover, January 2009, p. 28-29; “Science News of the Year: Humans,” Science News, January 3, 2009, v. 175, no. 1, p. 18.
8. The Cro-Magnons were the successors of the Neanderthals and lived from 35,000 to 10,000 years ago. They were highly skilled nomadic hunters, formed living groups of various sizes, and were also skilled cave painters.
Figure 19.17 Pleistocene Cro-Magnon Camp in Europe
Figure 19.18 Cro-Magnon Cave Painting
9. Since the appearance of Cro-Magnons, human evolution has become almost entirely cultural rather than biological.
Enrichment Topic 6. The Little People of Flores.
Ever since the diminutive skull and partial skeleton of a tiny human were discovered on the Indonesian island of Flores, paleontologists have been arguing the identification of the find. Currently dubbed a new species, Homo floresiensis, the individuals reached the island a minimum of 38,000 years ago, and survived until 12,000 years ago. An adult female probably stood 3 feet, 3 inches tall and weighed approximately 35 pounds. Some researchers propose an early arrival for Flores man on the island, and evolutionary “dwarfing” in which species evolve into smaller creatures from larger ones. Flores man would have been in existence at the same time as Homo sapiens, but there is no evidence that the two species ever interacted. Not all scientists are in agreement with the hypotheses, however, and propose that the fossils do not represent a new species, but genetic defects that were prevalent in the population. The debate continues. “Evolutionary Shrinkage,” Science News, Oct. 30, 2004, v.166. n.18 p. 275.; “Encore for Evolutionary Small-Timers,” Science News, Oct. 15, 2005, v.168 p.244-245.
In more recent studies of the “hobbit,” Adam Gordon at the University of Albany found that the skull was “well outside the range of modern human variation.” The size and shape of the skull are more similar to Homo habilis. William Jungers of Stony Brook University found that the hobbits’ feet were large in propotion to its body. However, Robert Eckhardt of Penn State Univeristy claimed that DNA isolated from the remains of the hobbit matches the DNA of Homo sapiens. Bosveld, “Hobbit Humans: Small Head, Big Feet,” Discover, January 2009, p. 68.
The Phylogeny of Humans
A 90-minute activity that utilizes the early technique of DNA-DNA hybridization can be used to illustrate the genetic difference between the human and ape superfamily, Hominoidea. Complete directions and suggestions can be found in “Building a Phylogenetic Tree, The American Biology Teacher, Oct. 2004, v.66 n.8 p.560-566.
The Human Factor
1. Discuss with your students which characteristics make an organism “human.” Although historic delineations between humans and non-humans involved burying of the dead, using tools, and creative expression, some of these traits have been exhibited by non-modern humans or other organisms. Which characteristics—other than physical differences—can be used to illustrate the “human” trait?
2. Evolution proceeds by natural selection, but can natural selection operate in the human population? What happens to children who are born with genetic abnormalities? Does the “survival of the fittest” apply to humans? What are the possible ramifications of this for our species in the future?
3. Remind students that the study of humans transcends two disciplines, physical anthropology and paleontology. How might these two different types of scientists approach the topic of human evolution?
The Evolution of Man
A controversial direction to explore in discussion of the evolution of man involves the discussion of science and religion in human origins. The late Stephan J. Gould wrote interesting essays that discussed evolution and creation in Bully for Brontosaurus. In "Knight takes Bishop?" the story of T.H. Huxley is told. Huxley eloquently and effectively challenged the clergy; he summarized that he would prefer to have an ape than the Bishop for an ancestor. The story highlights the tremendous emotion that has overpowered—and continues to overpower—any realistic discussions of evolution in the United States. (It may help your students to know that Gould was considered to be a spiritual man who also accepted evolution. His position was that the two realms exist separately and independently from each other.)
1. Discuss the emotion that the topic of human evolution inspires in many. Should the federal government regulate what is taught in the public schools with regards to evolution?
2. Nothing in science seems to change as much as the identity of our human ancestors. While those studying human evolution do not doubt that humans and other primates share common ancestors, the story continually evolves with the discovery of new fossils, the resultant interpretations, and new techniques of analysis. Discuss with the students that debates within the scientific community do not show a lack of support for evolutionary theory or human evolution in general. Are there any subjects within geology that have not been debated when a new hypothesis was proposed?
3. How do humans affect Earth when compared with other species? Are the impacts for
the benefit or the detriment of the Earth?
Software and Demonstration Aids
1. Neanderthal Man Reconstruction Kit, The Discovery Channel
13. Prior to the discovery of fossils of Australopithecus anamensis from Ethiopia, the origin of Australopithecus had been hampered by a sparse fossil record. The discovery of Ardipithecus in the same region of Africa, at the same time, provided evidence that Ardipithecus evolved into Australopithecus and links the two genera.
14. Primates have an arboreal, insectivorous ancestry. Evolutionary trends are toward diverse skeletal modifications, different modes of locomotion, increased brain size, a shift to smaller and more generalized teeth, stereoscopic vision, and a grasping hand with an opposable thumb.
15. Compared to Homo sapiens (including Cro-Magnon), Neanderthals had a shorter, more robust and powerful physique, typical of human adaptation to cold climates. They also had an elongate skull with a reduced frontal lobe area and extended occipital region, larger brow ridges, and a receding chin. Their cranial capacity was slightly larger than that of modern humans, but their brain mass was distributed differently.
16. The genus Homo includes H. habilis, H. erectus, the Neanderthals (H. neanderthalensis or the alternative, H. sapiens neanderthalensis), and H. sapiens. H. habilis (2.5-1.6 million years ago) was an African form that apparently used tools; the larger, and larger brained H. erectus spread out of Africa to India, China, and Indonesia. Neanderthals, found from the Mid-east through western Europe, had a shorter, more robust physique and flatter skull, more prominent brow ridges, and receding chin compared to later H. sapiens; many of their physical adaptations seem related to cold climate survival. Early modern H. sapiens, as exemplified by Cro-Magnon (35,000-10,000), were essentially the same physiologically as fully modern humans, and had complex culture compared to all earlier members of the genus Homo.
17. Anthropoids evolved from prosimians in the Late Eocene. In North Africa, rain forests supported a diverse fauna of prosimians, one of which gave rise to a very similar early anthropoid. Anthropods are divided into three superfamilies: Old World Monkeys, New World monkeys, and Hominoids. The Hominoids evolved, and consist of three families: the great apes, the lesser apes, and the hominids, which represent humans and their ancient ancestors.
18. Hominids include humans (Homo) and their extinct ancestors. Their fossil record extends back about 7 million years. The hominids are distinguished by several features, including bipedalism, large and internally reorganized brains, reduced faces, reduced canine teeth, omnivorous feeding, increased manual dexterity, and use of sophisticated tools. There is no clear consensus on the evolutionary history of hominids. However, the oldest hominid known is Sahelanthropus tchadensis, which existed near the time that hominids diverged from the chimpanzees. This organism exhibits a small brain case and chimp-like teeth, but it was probably bipedal, and had a flat nose and brow ridges. Later, the genus Ardipithecus evolved, followed by the genus Australopithecus. Finally, the genus of modern humans, Homo, evolved. Hominids share the hominoid superfamily with great and lesser apes.
19. Prosimians are the lower primates and include lemurs, tarsiers, lorises, and tree shrews. They are small, arboreal, mostly nocturnal, and closely resemble their Paleocene roots. Anthropoids are the higher primates and include monkeys, apes, and humans. They are larger, smarter, more diverse, and more derived primates; they arose in the Late Eocene.
20. According to the “out of Africa” view, 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 earlier hominid populations to extinction. The supporters of the “multiregional” view contend that early modern humans did not have an isolated origin in Africa but 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.
Apply Your Knowledge
1. There may be many different student views with this question. However, given that human evolution does not necessarily operate according to natural selection, changes in the human population are not necessarily driven by the “survival of the fittest.” Technological advances allow us to keep those individuals with genetic abnormalities alive, when they would have died in the past. From a human standpoint, this may be a morally good thing. However—as most microbiologists would concur—this is not a good thing for evolution! As individuals with genetic flaws mature, they are able to reproduce, perpetuating less-than-desirable genes in the population. With technological advances, the removal of “bad genes” from DNA may one day be a possibility. Recently, a baby was born which was genetically selected not to have a cancer gene. Will parents be able to code for various traits of their offspring? Will the population become skewed toward certain characteristics (sex, hair color, eye color, height, body shape) that people deem “desirable?” The moral and genetic implications of this type of technology will be great, and it may not lead to diversity in the next 5000 years if all parents desire the same traits for their children.
2. Student answers will vary greatly. Some students may take a very broad “history of life” view, and trace human evolution from the first vertebrates (fish), to amphibians, reptiles, mammal-like reptiles, mammals, primates, anthropoids, hominoids, hominids, through Homo sapiens. Other students may choose to focus upon more recent hominids, especially the Neanderthals, who resembled Cro-Magnons in most features. Evolution since the appearance of Cro-Magnons has been largely cultural, and some students may focus upon that.
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