Chapter 19

1. Chapter 19 Human Evolution

2. How Are We Related to Neanderthals? • Neanderthals were an evolutionarily recent human relative that lived in Europe until about 30,000-40,000 years ago • Neanderthals lived alongside Cro-Magnons, direct ancestors of present-day Europeans • Did the two groups interbreed so that vestiges of Neanderthals survive in modern humans? • Analysis of DNA isolated from Neanderthal bones has shown that Neanderthals were a distinct species from modern humans

5. PRIMATE DIVERSITY • 19.1 The human story begins with our primate heritage • The mammalian order Primates includes the lemurs, tarsiers, monkeys, and apes • Primates had evolved as small arboreal mammals by 65 million years ago • Most living primates are arboreal • Humans retain in their bodies many traits that evolved with our arboreal relatives

6. Primate features include • Limber joints • Grasping hands and feet with flexible, sensitive digits • A short snout • Forward-pointing eyes that enhance depth perception • The squirrel-sized slender loris illustrates a number of primate features

8. The lorises, lemurs, and pottos make up the oldest group on the primate phylogenetic tree • All live in tropical forests, and all are threatened by habitat destruction • Tarsiers, the second branch, are small, nocturnal tree-dwellers living in Southeast Asia • Tarsiers are more closely related to anthropoids than to the loris-potto group

9. Anthropoids LE 19-01b Monkeys Hominoids (apes) 0 Chim- panzees Humans Gorillas Tarsiers Gibbons Orangutans 10 Old World monkeys New World monkeys Lorises, pottos, and lemurs 20 30 Millions of years ago 40 50 Ancestral primate 60

12. The anthropoid group includes monkeys and apes • Humans are members of the ape group (hominoids) • Anthropoid features include • Larger brain relative to body size • More reliance on eyesight • Opposable thumb • Anthropoids began diverging from other primates about 50 million years ago

13. Monkeys do not constitute a monophyletic group • New World monkeys are found in Central and South America • All are arboreal • Nostrils are wide open and far apart • Many have a prehensile tail • Old World monkeys • Lack a prehensile tail • Nostrils open downward

16. Monkeys differ from most apes in having forelimbs about equal in length to hind limbs • Old World monkeys and apes diverged about 20-25 million years ago • The human ancestry probably diverged from an ancestor shared with chimpanzees between 5 and 7 million years ago

17. 19.2 Hominoids include humans and four other groups of apes • Hominoids include gibbons, orangutans, gorillas, chimpanzees (and bonobos), and humans • Are chiefly vegetarians • Lack tails • Have longer forelimbs than hind limbs • Have relatively large brains • Apart from humans, have a limited geographical range in the tropics

18. Gibbons are the only entirely arboreal apes • Found in Southeast Asia • Only nonhuman monogamous ape • The orangutan is a shy, solitary species • Largest living arboreal animal • Lives in rain forests of Sumatra and Borneo

21. The gorilla is the largest ape • Found only in African rain forests • Usually live in groups of up to 20 individuals • Spend nearly all their time on the ground • Chimpanzees and bonobos spend a quarter of their time on the ground • Knuckle walkers, like the gorilla • Inhabit tropical Africa

24. Video: Gibbons Brachiating Video: Chimp Agonistic Behavior Video: Chimp Cracking Nut

25. Many aspects of chimpanzee behavior resemble human behavior • Make and use tools • Raid other social groups of their species • Can learn human sign language • Seem to be self-aware • Gorillas and chimpanzees are more closely related to humans than to other apes • Chimpanzees are our closest living relatives, sharing more than 99% of our genes

26. HOMINID EVOLUTION • 19.3 The human branch of the primate tree is only a few million years old • Paleoanthropology studies human origins and evolution • Humans and chimpanzees diverged from a common ancestor 5 to 7 million years ago

27. A number of derived characters distinguish humans from other hominoids • Bipedal • Shorter jaws • Larger brain • Capable of language and complex thought • Manufacture and use complex tools • Long-term pair-bonding between mates • Longer period of parental care

28. Hominids are extinct members of the human branch of the evolutionary tree • Oldest hominid: 7 to 6 million years ago • Australopiths: Between 4 and 2 million years ago • Do not represent a monophyletic group • Some overlapped with the genus Homo • At times, several hominid species coexisted; all but our own are extinct

29. LE 19-03 0 Homo ergaster Paranthropus robustus ? 0.5 Paranthropus boisei 1.0 Homo sapiens 1.5 Australopithecus africanus Homo neanderthalensis 2.0 Australopithecus afarensis 2.5 Homo erectus 3.0 Australopithecus anamensis Millions of years ago 3.5 Homo habilis 4.0 Kenyanthropus platyops 4.5 Ardipithecus ramidus 5.0 5.5 6.0 Orrorin tugenensis 6.5 Sahelanthropus tchadensis 7.0

30. 19.4 Upright posture evolved well before an enlarged brain in hominids • Footprints left by Australopithecus afarensis indicate that hominids have been bipedal for at least 3.5 million years • An important clue to bipedalism is the spinal cord exit at the base of the skull, allowing an upright position • "Lucy," a fossil dating back 3.24 million years, indicates that A. afarensis was small brained, small in stature, and bipedal • Whatever the selective pressure for bipedalism, it evolved before an enlarged brain

31. LE 19-04 Lucy, a 3.24- million-year- old skeleton Ancient footprints

32. 19.5 Larger brains and reduced sexual dimorphism mark the evolution of Homo • Homo habilis (about 2.4 million years ago) • Had a larger skull and used tools • Homo ergaster (about 1.9 to 1.6 million years ago) • Had a larger brain than H. habilis • Used more sophisticated tools • Showed less size difference between sexes

33. Sexual dimorphism may offer some clues to the social system of extinct hominids • Less dramatic in species that exhibit pair-bonding • May be associated with long-term parental care by both parents • Homo erectus was the first hominid to migrate out of Africa, eventually as far as Indonesia

34. 19.6 When and where did modern Homo sapiens arise? • Homo sapiens evolved in Africa and later migrated to Asia and Europe in one or more waves • Earliest H. sapiens fossils from Ethiopia support molecular evidence about human origins • Europeans and Asians share a more recent common ancestor than H. neanderthalensis • Many African lineages represent early branches on the human family tree

36. Mitochondrial DNA and Y-chromosome analyses support divergence from a common African ancestor who lived 100,000-150,000 years ago • Recently found 18,000-year-old H. floresiensis fossil represents a previously unknown hominid species • The rapid expansion of humans may have been related to their creativity and increased cognition • Evidence of sophisticated thought in 77,000-year-old art

38. CONNECTION • 19.7 Human skin colors reflect adaptations to varying amounts of sunlight • Dark skin color protects against UV-induced loss of folate, necessary for fetal development • Why aren't all humans dark skinned? • UV radiation catalyzes vitamin D synthesis • Dark-skinned humans evolving in equatorial Africa received sufficient UV radiation • Loss of pigmentation allowed humans migrating to northern latitudes to receive sufficient UV

39. CONNECTION • 19.8 A genetic difference helped humans start speaking • Language and complex, abstract communication permit the creation of human cultures • A mutation in the FOXP2 gene has been linked to human language ability • Likely arose within the last 100,000 years, matching emergence of Homo sapiens

41. OUR CULTURAL HISTORY AND ITS CONSEQUENCES • 19.9 Culture gives humans enormous power to change the environment • Human culture is the accumulated knowledge, customs, arts, beliefs, and other products socially transmitted over generations • Evolutionary basis: growth in brain size and complexity during childhood, allowing children to learn from the experiences of earlier generations

42. Culture has made Homo sapiens a unique force in the history of life on Earth • We can change the environment to meet our needs at a faster rate than biological evolution • We have been able to transcend our physical limitations at the expense of other species and the environment

43. 19.10 Scavenging, gathering, and hunting were the earliest human endeavors • Scavenging, gathering, and hunting • Were how the earliest hominids lived • Continued to be the way of life for australopiths and species of Homo • Were the norm for Homo sapiens during most of the last 100,000 years • Continue today in some societies

44. Toolmaking • Led to hunting becoming a major source of food • Allowed humans to profoundly affect other species • Origins of agriculture • Communal activities • Divided labor • Semipermanent residences

46. 19.11 Agriculture was a major development in human history • Agriculture developed in Africa, Eurasia, and the Americas about 10,000 to 15,000 years ago • Began in the Fertile Crescent of the Middle East • Patterns of overuse and changes in climate turned the Fertile Crescent into the desert of today • Farming was the first step in Homo sapiens becoming the dominant species on Earth

48. 19.12 Development of complex tools affects human culture and the world • The Industrial Revolution that began in the 1700s initiated a change to energy-intensive, large-scale machine production • More food production and medical advances led to a rapidly growing human population • The speed of technological change outpaces biological change, jeopardizing many species and perhaps ourselves