Humans in the Natural World

1. Humans in the Natural World • Humans are vertebrates with, among other features: 1. an internal, segmented vertebral column 2. an internal, segmented skeleton. 3. bilateral symmetry. • Humans are also mammals, with: 1. maintenance of constant body temperature. 2. birth of live young. 3. mammary glands to nurture the young over a prolonged period of growth and development. 4. large brain associated with ‘intelligence’ 5. A dentition made up of several different kinds of teeth (incisors, canines, premolars and molars) that function together to allow the animal to chew.

2. Humans in the Natural World • Humans are Primates: 1. Basic adaptations to life in the trees (arboreal way of life). 2. The retention of the five digit hand and foot. 3. Development of acute vision with depth perception. 4. Relative lack of an acute sense of smell. • Humans are Higher Primates (with monkeys, apes): 1. Social Living 2. Daytime activity cycles (diurnal) 3. diverse dietary patterns.

9. Chimpanzees as Humans in fur suits • Because of their biological and behavioral similarities to humans, chimps are often used as models of what our earliest ancestors were like. • The major problem with this is that living chimps are the result of a separate evolutionary history as long as ours, and they may have changed as profoundly as we have. • There is not a single fossil bone documenting the evolutionary history of either chimps or gorillas.

11. Human Origins in Africa • Our closest living relatives, the African apes, the chimpanzee and gorilla, are both native to Africa. (It should be emphasized, again, however, that there is no fossil evidence documenting the evolutionary history of either of these two primates.) • All of the earliest fossil evidence of our own evolutionary history is limited to Africa, and it is only relatively late in human evolution that our ancestors are found in Eurasia. • There are fossil deposits of this early time in Europe and Asia, and they show no trace of our early ancestors.

12. What’s in a name? • Although there is much debate about what terms to use when referring to our extinct ancestors, in this class, we will call them hominids, and speak of human evolution as the evolution of the hominids. • Thus, we can say that hominid evolution seems to have begun in Africa, and it is only much later in our evolutionary history that we find signs of our ancestors outside the African continent.

15. The Time of Human Origins • Studies of the genetic similarity of humans, chimps and gorillas indicate that we last shared a common ancestor with these animals between 5-8 million years ago. • Human evolution can be said to begin at that time. • Currently, we have definite fossil evidence earliest from about 4.4 million years (myr), and recent discoveries now suggest hominids were around at 6 myr. If the earliest of the genetically derived dates is correct (8 myr), then we have fossils documenting only the last half of human evolution. If the later date is correct (5 myr), then it would now appear that we have the earliest fossils of the hominid line, and these irtually the entire human fossil record and the earliest fossils should be expected to document our initial beginnings.

16. Human Origins humans chimpanzees gorillas Hominid evolution 5 - 8 myr 10 myr. common ancestry of humans and African apes An evolutionary diagram of human and African ape relationships, based on various genetic studies

17. What is a human? As Profs Liberman and Urban have already noted, modern humans are unique in having: 1. Complex culture with a wide variety of societal norms in behavior. 2. Language and symbolism. 2. Biologically: very large brains in comparison to our body size. small, non-projecting faces. bipedal locomotion. The major question here is: when did these distinctive features of modern humans appear in the course of our evolution?

18. Identifying the Human Lineage • The single most important feature in identifying a fossil as a hominid is bipedalism. This appears to be the earliest major change in our evolution and fossil evidence for erect posture has become the most important defining feature of the hominids. • There are also major changes in the the teeth. Apes possess large, projecting canine teeth, while hominids have reduced canines.

20. Evidence for Human Evolution • Comparative Anatomy The examination of the gross anatomical features of humans and apes reveals their close similarity. • Comparative Genetics Comparisons of the genetic materials of the African apes and humans documents that these creatures are more closely related to each other than to any other living animal. • Fossil Evidence

21. Fossil Evidence • The direct evidence of our extinct ancestors. • Other evidence documents relationships; only fossil evidence provides data on the biology and adaptation of our actual ancestors. • Because of the nature of the fossilization process, this evidence is often difficult to fully understand and interpret.

29. The Human Fossil Record • Definite fossil evidence documents a beginning more than 4 million years ago; recent finds of fossils from western Kenya dated to more than 6 million years ago (‘Millennium Man’) suggests a much older origin. • The earliest evidence is of animals possessing some biological traits like those of modern humans, some that resembled the apes, and many unique traits. • Later-in-time hominids look more and more like living people. • Based on anatomical features of the skull, teeth and body size, a number of different genera and species have been proposed.

31. The Earliest Hominids • Found in 1994 in East Africa, these creatures are called Ardipithecus ramidus. • A considerable number of fossil bones of Ardipithecus have been found ; they are dated to about 4.4. million years ago. • The fossil bones are currently being studied, and not much has been published about these creatures. • It is known that they were bipedal, and unlike any later hominids, and like the apes, they had thin layers of enamel on their back molar chewing teeth. • Most anthropologists believe that Ardipithecus represents an side branch of human evolution that had no descendents.

34. The Earliest Hominids 2 Homo 3 4 Australopithecus Ardipithecus 5 6 millions of years ago

35. The Australopithecines • First identified by Raymond Dart in 1925. The fossil was that of a young child from the site of T’aung which is a limestone quarry in the Cape Province of South Africa. • Dart examined the fossil and found several features he believed identified this child as a human ancestor. • He named the fossil Australopithecus africanus (‘the southern ape of Africa’).

38. A Question to Consider If you did not know about the fossil evidence, how many of you would have expected our early ancestors to be distinguished first and foremost by increased head size? This is, after all, the seat of our intelligence and ‘humanness’.

39. The Australopithecines • All are bipedal and therefore hominids. • Now known from sites in East, South and Central Africa. • They are dated from about 4 to about 1.5 million years ago. • On the basis of differences in features like size of the teeth, the brain and body, the australopithecines have been divided into more than six species.

42. The Australopithecines Although there are at least six recognized species, all australopithecines possessed in common the following: 1. the anatomy of bipedalism. 2. small, non-projecting canines. 3. incisors not much bigger than in humans. 4. back chewing teeth, the premolars and molars that were huge. 5. very large jaws and jaw muscles.

43. The Australopithecines 6. australopithecines had small brains: volumes range from 400-500ml. By comparison: modern humans: 1400m. chimpanzees: 375m. gorillas: 500ml. (1000 ml = 1 liter, 1 US quart = 946 ml.)

45. Australopithecus afarensis • Although not the earliest of the australopithecine species, this is one of the most famous, with many fossils, and other evidence, unearthed from sites in East Africa: Hadar (Ethiopia) and Laetoli (Tanzania). • Dated between 3.7 -2.9 myr. • At Laetoli (3.7 myr), in addition to fossil bones, Mary Leakey found three footprint trails. • At Hadar (3.2-2.9myr), many fossils have been found including the most complete australopithecine known: about 40% of a skeleton called ‘Lucy’.