31/10/2012. Human Evolution. Cytochrome c DNA tree

Transcription

1 Human Evolution Cytochrome c DNA tree 1

2 Human Evolution! Primate phylogeny! Primates branched off other mammalian lineages ~65 mya (mya = million years ago) Two types of monkeys within lineage 1. New World Monkeys (Americas): spider monkey; howler 2. Old World Monkeys (Africa, Asia/Polynesia): rhesus; grenons; Sooty mangabeys (source of HIV-2) OW/NW split 35-40mya (fossil record) OW/humans and apes split (25-30mya) Tree based on strength of immune reactions of human serum albumin antibodies in other primates. Assuming constant rate of evolution, and calibrated with OW split at 30 mya. Phylogeny of human, chimp and gorilla was not initially resolved. 2

3 Scientists have discovered that humans and chimpanzees are 99% the same drink GUINNESS Origin of humans! Split between human and chimp lineage occurred at least 5 mya (9-7 mya) Hominid = extinct and extant species more closely related to humans than to chimps Examination of Hominid evolution was originally based on fossil evidence BUT: - Fossils are rare - Fossils are incomplete Difficult to differentiate evolutionary differences from within-species variation (esp. sexual dimorphism = differences between sexes; e.g. size ) 3

4 Oldest Hominid fossil?? cranium, jaw fragment, and tooth from Chad dated to 6-7 mya some researchers disagree with classification as Hominid, say it is the skull of an adult female gorilla NOTE: if on Hominid lineage is inconsistent with estimates of divergence with chimp Few fossils between 5-4 mya found in Ethiopia Ardipithecus (shown) Most fossils dated after 4.2 mya & before Homo are called Australopithecus Australopithecus afarensis Famous fossil Lucy (after Lucy in the Sky with Diamonds ) -dated 3.2 mya Laetoli footprints (3.5 mya) which showed bipedalism (some paleontologists think that bipedalism was the most important step in human development; others say it was speech; others admit we don t actually know yet!) Australopithecus was present in many areas in Africa from mya Homo erectus earliest Hominid found outside Africa. Found in Indonesia and China 4

5 Fragmentary fossil evidence - reconstructed phylogeny from 77 morphological traits from 7 anatomical regions Note: 1. Evolutionary tree is branched older fossils are not necessarily ancestors of anything living 2. can get some convergent evolution (=same change/adaptation independently)->not necessarily good measures Homo erectus Early Homo erectus Turkana Boy (11 year old) 1.6 mya Believed to be first hominid that spread out of Africa probably 1 mya By 730,000 BP (before present) H. erectus had colonized Middle East and S. Europe 500,000 BP Germany, Britain, Peking brain size increased 5

6 Neanderthal evolved from H. erectus outside Africa Early European Appeared ~120,000 BP originated in Middle East evidence for presence 115,000-35,000 BP (some mixture with modern humans) Transition to Modern Humans -some H. erectus evolved into H. sapiens in Africa excellent fossil sequence ancient -> modern -H. sapiens probably arose 200, ,000 BP -Was this transition unique to Africa? Two main models: (plus intermediates) 1. Multiregional 2. Out of Africa (African replacement, monoregional) 6

7 Multiregional Predictions: -last common ancestor of modern humans is H. erectus that radiated from Africa -Why evolve same characteristics independently in different places? ->Behavioural; cultural exchange; universal selection forces Out of Africa Predictions: -last unifying event more recent only 100,000 BP (ten times less) -H. sapiens radiated from Africa -only arose once -extinction of other Homo species 7

8 Which model is supported by the molecular evidence? 1. The relationship of modern humans to archaic humans - The multiregional model predicts that modern Europeans are descendents of archaic Europeans (Neanderthals). - DNA was extracted from the Neanderthal skeleton bones by Svante Paabo. Analysis showed that it is completely distinct from modern humans (not close to Europeans) and diverged very long ago. The timing and pattern of relationships are consistent with the Out of Africa model. 8

9 Geographic patterns of diversity Greater diversity in the location of origin Origin Diversification Migration of some individuals -> high diversity in the epicentre bottleneck : -> low diversity in these new territories The timing of the divergence of modern humans The predicted date of the last common ancestor of modern humans is very different between the two models. The multi-regional model predicts that the last common ancestor existed prior to the migration of H. erectus out of Africa (1.5-2 mya). The Out of Africa (replacement) model predicts a much more recent common ancestor, at the time of H. sapiens migration out of Africa (100, ,000 ya). Estimate this date using a molecular clock 9

10 Genetic evidence supports African origin -most genetic diversity is seen within Africa oldest group of humans -H. sapiens originated in Africa -some individuals migrated took a subset of genetic variation with them -some members of lineage didn t migrate -> see diversity unique to Africa Last common ancestor of H. sapiens is too recent to be compatible with multiregional hypothesis. Molecular data indicate that H. sapiens left Africa ~ 100,000 BP 10

11 Migration is ongoing Migrants from around the world have contributed to the genomes of some South Africans. 11