Origin of Homo sapiens

1. Origin of Homo sapiens • Paleontologists disagree about the taxonomic status of H. ergaster • Same species as H. erectus or different? • New H. erectus fossil recently found in Georgia from 1.75 Mya • There is also disagreement about status of H. neanderthalensis • Species or subspecies of H. sapiens? • H. antecessor may be ancestor of H. sapiens and H. neanderthalensis

2. Origin of Homo sapiens • Hypotheses about transition from H. erectus/ergaster to H. sapiens • African Replacement (Out of Africa) • H. sapiens evolved in Africa, migrated to Europe and Asia, and replaced H. erectus and H. neanderthalensis without interbreeding • Candelabra • H. sapiens evolved separately in Europe, Africa, and Asia without gene flow among regions • Two extreme models

3. Origin of Homo sapiens • Hypotheses about transition from H. erectus/ergaster to H. sapiens • Other models between two extremes • Hybridization and Assimilation • H. sapiens evolved in Africa and migrated to Europe and Asia with some amount of hybridization • Some European and Asian genes were assimilated and persist into modern humans

4. Origin of Homo sapiens • Hypotheses about transition from H. erectus/ergaster to H. sapiens • Multiregional Evolution • H. sapiens evolved concurrently in Europe, Africa, and Asia with sufficient gene flow to maintain their continuity as a single species • Current gene pools are a mixture of all of these regional variants

6. Origin of Homo sapiens • Which hypothesis has most supporting evidence? • Are human racial differences due to separate evolution 1.5–2 Mya (Candelabra) or are races recently evolved 100,000– 200,000 ya (African Replacement)? • Candelabra has been widely rejected • A single species could not evolve independently in three places at the same time

7. Origin of Homo sapiens • Frayer argues that the only way African Replacement can be correct is if African H. sapiens had superior tools to allow him to defeat H. erectus • No such archaeological tool record has been found • Frayer also argues that Australian aborigines have similar features to Java Man (Homo erectus) • Rejects African Replacement

8. Origin of Homo sapiens • Lieberman and Waddle predict cladograms based on African Replacement and Multiregional Evolution models • Predicts the relationships of modern humans • Can be tested with molecular evidence

10. Origin of Homo sapiens • Paabo recovered a mtDNA sequence from a H. neanderthalensis skeleton • From Germany 30,000–100,000 ya • Also sequenced 663 modern humans, 7 chimpanzees, and 2 bonobos • Found that modern humans from Europe, Africa, Asia, America, Australia, and Oceania are more closely related to each other than any is to H. neanderthalensis • Estimated divergence of Neandertal to modern humans to be 317,000–741,000 ya • Supports African Replacement model

12. Origin of Homo sapiens • Researchers test models with modern sequences only • Problem is that prediction in the same for African Replacement and Multiregional Evolution • Just time scale is different • Out of Africa model says differentiation of races began 200,000 ya • Multiregional Evolution model says it began 1.8 Mya • Quantitative rather than qualitative differences

14. Origin of Homo sapiens • Hedges tested models with mtDNA • Remember mtDNA is maternally transmitted • 189 people produced phylogeny which lead back to a single woman from Africa • Mitochondrial Eve • Of course there was not a single woman that gave rise to all of these 189 people • Many indirect female ancestors who lived at the same time

17. Origin of Homo sapiens • Hedges study does not only support African Replacement model • All models predict ultimate ancestor to be from Africa • Vigilant estimated common ancestor of all present-day mtDNA lived 166,000–249,000 ya • Ruvolo estimated it to be 129,000– 536,000 my • Horai estimated from entire mtDNA genome to be 125,000–161,000 ya

18. Origin of Homo sapiens • All of these dates are similar and seem to support African Replacement model • Because mtDNA is effectively all a single gene, we need independent estimates of age of split • mtDNA may be estimating the split to be too young • Populations connected by gene flow may diverge after their alleles do

20. Origin of Homo sapiens • Bowcock examined 30 nuclear microsatellite loci from 14 human populations • Deepest split in their phylogeny is African from non-African populations • Split occurred 75,000–287,000 ya • Support for African Replacement model

22. Origin of Homo sapiens • Tishkoff examined allelic variation on Chromosome 12 • Short tandem repeat polymorphism • Examined amount of allelic diversity in populations around the world • Found African populations had highest allelic diversity • Dated split to be 102,000–450,000 ya • Consistent with African Replacment

23. Evolution of Uniquely Human Traits • Humans walk bipedally, have very large brains, use complex tools, and use language • Chimpanzees and other animals make and use tools • Only humans make and use complex tools • First tools were stone flakes and choppers • Oldowan Industry

25. Evolution of Uniquely Human Traits • Oldest Oldowan tools from Gona, Ethiopia 2.5–2.6 My old • Who made these tools? • Oldest Homo fossil is 2.3 My old • Homo habilis • Maybe robust australopithecine • They had three hand muscles that chimpanzees lack • Like modern humans do • Increased grasping ability

27. Evolution of Uniquely Human Traits • Susman hypothesized that new muscles evolved in response to selection for complex tool use • A. afarensis did not have these specialized muscles • We cannot know for certain whether Homo was first tool user or a robust australopithecine

29. Evolution of Uniquely Human Traits • Which hominid first used language? • Because language is a behavior, it cannot fossilize • Language is a complex adaptation involving neural circuitry in brain • Appears to be an innate trait in humans • Also involves adaptations of throat • In apes and human babies larynx is high in the throat and seals with nasal cavity to prevent choking

30. Evolution of Uniquely Human Traits • Which hominid first used language? • In mature humans, larynx is lower to allow greater diversity of sounds • Increases choking risk • Some archaeologists argue that language cannot be proven without arbitrary symbols • Cave paintings in Europe 32,000 y old • But humans built boats and travelled to Australia by 40,000 ya • Must have had language to accomplish this

31. Evolution of Uniquely Human Traits • Which hominid first used language? • Fossils of larynx offer other evidence • Neandertal larynx appears to have been undescended • A 60,000 y old Neandertal skeleton from Israel had an intact hyoid bone • Anchors throat muscles in larynx • Found hyoid bone to be nearly identical to modern humans and completely different from chimpanzees • Indicates a descended larynx • Probably could speak

33. Evolution of Uniquely Human Traits • Which hominid first used language? • What about brain ability? • Brain size increased steadily in Homo • Enabled early man to speak • Costly because large brains require much energy to maintain • Endocasts reveal similar brain structure to modern humans • Including speech centers of brain • Language may be 2 My old