Arriving Late, Traveling Far: The Evolution of Human Beings

1. Arriving Late, Traveling Far:The Evolution of Human Beings

2. 20.1 The Human Family Tree

3. The Human Family Tree • Human evolution is the study of the taxonomic grouping called the Hominini or human-like primates. • Every member of this group is referred to as a hominin, including human beings.

4. The Human Family Tree • A common primate ancestor is believed to have given rise to both the chimpanzee and the human family evolutionary lines between 6 and 7 Mya.

5. The Human Family Tree • The structure of the hominin tree is a matter of considerable debate among researchers. • We do not have enough fossil evidence to say with certainty which species were ancestral to which others.

6. 20.2 Human Evolution in Overview

7. Human Evolution in Overview • All the members of the hominin grouping are extinct except for Homo sapiens, the human species. • Human beings were late in arriving among the hominins, but all hominins are late arrivers when the entire sweep of evolution is considered.

8. Human Evolution in Overview • Until the past 10 years, evidence indicated that most early- and mid-period hominin evolution took place in east Africa.

9. Human Evolution in Overview Africa Chad Sahelanthropustchadensis Ethiopia Earliest modernhuman(Homo sapiens) Kenya Australopithecusfossil discoveries Orrorintugenensis Paranthropusfossil discoveries Tanzania Australopithecusand Ardipithecusfossil discoveries South Africa Indian Ocean Figure 20.2

10. Human Evolution in Overview • But in 2002, the range of likely hominin fossils was expanded 2,500 kilometers to the west, to Chad, with the discovery of the 6- to 7-Mya remains of a primitive hominin named Sahelanthropus tchadensis or Toumaï.

11. Human Evolution in Overview A Hominin Family Tree H. sapiens Present recent H. neanderthalensis H. heidelbergensis H. floresiensis H. mauritanicus Pleistocene 1 H. cepranensis H. erectus H. habilis P. robustus 2 K. rudolfensis P. boisei Homoergaster Au. garhi Au. africanus Paranthropusaethiopicus 3 Au. bahrelghazali Pliocene Millions of years ago Au. afarensis Kenyanthropusplatyops 4 Australopithecusanamensis Ar. ramidus 5 chimps gorillas monkeys hominins orangutans Ardipithecuskadabba Orrorintugenensis 6 Sahelanthropustchadensis ancestral primate 7 Figure 20.1

12. 20.3 Interpreting the Fossil Evidence

13. Interpreting the Fossil Evidence • In human evolution studies, molecular evidence—usually the sequencing of DNA—has increased in importance in recent years. • But the primary evidence in the field remains fossil evidence.

14. Interpreting the Fossil Evidence Africa Chad Sahelanthropustchadensis Ethiopia Earliest modernhuman(Homo sapiens) Kenya Australopithecusfossil discoveries Orrorintugenensis Paranthropusfossil discoveries Tanzania Australopithecusand Ardipithecusfossil discoveries South Africa Indian Ocean Figure 20.2

15. Interpreting the Fossil Evidence • The researchers who find and analyze hominin fossils are known as paleoanthropologists.

16. Interpreting the Fossil Evidence • Paleoanthropologists interpret features of fossils in order to make judgments about where a given fossil form lies in the hominin family tree. • Interpretations can differ, however.

17. Interpreting the Fossil Evidence • The two most important defining characteristics of a hominin are tooth structure and upright or “bipedal” walking.

18. 20.4 Snapshots from the Past: Three Hominins

19. Australopithecus afarensis • The bipedalism seen in our own species clearly existed in the hominin species Australopithecus afarensis, whose most famous individual, Lucy, lived 3.18 Mya in what is now Ethiopia.

20. Australopithecus afarensis • Lucy had a much smaller brain than modern humans do, however, and she probably was partly arboreal, or tree-dwelling.

21. Australopithecus afarensis Smallerbrain Longer arms(shorter legs) Graspingfeet Figure 20.6

22. Australopithecus afarensis • Lucy’s set of features demonstrate that hominin features developed in a mosaic pattern—different features evolved at different points in time and in different species.

23. Australopithecus afarensis • Lucy’s species is generally regarded as being ancestral to the Homo genus that human beings are a part of. • Thus, Lucy probably is a human ancestor.

24. Three Hominims Figure 20.5

25. Homo ergaster • A change to a physical form and mental capacity much closer to ours comes with the evolution of Homo ergaster, exemplified by Turkana Boy, who lived 1.6 Mya.

26. Homo ergaster Figure 20.7

27. Homo neanderthalensis • In their modern form, the Neanderthals (Homo neanderthalensis) populated Europe as well as parts of Asia for about 130,000 years.

28. Homo neanderthalensis • The last of them died 28,000 years ago in Europe. • The modern caricature of the caveman comes from the Neanderthals, but this image is difficult to reconcile with facets of Neanderthal life such as the burying of the dead.

29. Homo neanderthalensis • Even given these facets, however, it is clear that the Neanderthals were a primitive species in comparison with H. sapiens.

30. 20.5 The Appearance of Modern Human Beings

31. The Appearance of Modern Human Beings • Human beings appear to have evolved into their modern anatomical form in Africa prior to the time they began to migrate into the wider world.

32. The Appearance of Modern Human Beings • This “out-of-Africa” hypothesis stands in contrast to the less-accepted “multiregional” hypothesis, which holds that several species of hominins migrated from Africa at different times, interbred, and evolved into H. neanderthalensis and H. sapiens.

33. The Appearance of Modern Human Beings • The initial wave of human migration out of Africa was initiated sometime between 85,000 and 55,000 years ago.

34. The Appearance of Modern Human Beings Asia Easterly migration ArabianPeninsula Africa Niah Cave,Borneo Andaman Islands Humanoriginsin Africa Malay Peninsula Australia Indian Ocean Lake Mungo Figure 20.8

35. The Appearance of Modern Human Beings • The earliest fossils we have of modern human beings outside Africa and its immediate environs date from 46,000 years ago and were found in Australia.

36. The Appearance of Modern Human Beings • Molecular evidence indicates that modern human beings evolved no earlier than 200,000 years ago. • The earliest human fossils we have date from 195,000 years ago and were found in Ethiopia.

37. The Appearance of Modern Human Beings • The arrival of modern human beings in Europe 40,000 years ago was followed by the extinction of the Neanderthals 12,000 years later. • The arrival of human beings in the Far East, at least 46,000 years ago, was followed by the extinction of the Homo erectus species 6,000 years later.

38. The Appearance of Modern Human Beings • If there is a consensus about why we human beings are the only living species of hominin, it is that we “replaced” such species as H. erectus and H. neanderthalensis by out-competing them after having migrated to Asia and Europe.

39. 20.6 Next-to-Last Standing? The Hobbit People

40. Homo floresiensis • In 2004, researchers reported finding, on the Indonesian island of Flores, fossils of a previously unknown hominin, Homo floresiensis, who stood only 3 feet tall and seemed to have survived until 18,000 years ago.

41. Homo floresiensis • This interpretation of the Flores fossils has been challenged, however, by two teams of researchers who have concluded that H. floresiensis actually was a small, modern human being suffering from the medical condition of microcephaly.

42. Homo floresiensis Figure 20.9

43. Homo floresiensis • If H. floresiensis is a new species of hominin, one possibility is that it evolved from H. erectus.