360 likes | 616 Views
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
E N D
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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