Bio1B Evolution 12 Last lecture Fossil record Fossil record significance interpretation Extinction Background extinction rates and the big 5 mass extinction The K T boundary asteroid hypothesis dinosaur extinctions radiation of mammals Are humans causing the 6th mass extinction Today Macro evolution cont Species selection Transitional forms tetrapods birds exaptation Evolution of developmental programs eg vertebrate limbs Human evolution Evolutionary origins of Homo sapiens fossils molecular evidence 1 Are we the cause of the 6th mass extinction Barnosky et al Nature 2011 2 Macro evolution Species selection E g self incompatibility SI in hermaphroditic plants is often disdadvantageous within species compared to self compatibility SC BUT diversification rate S E higher in SI purple than SC blue E E Goldberg et al Science 2010 330 493 495 Evolution of particular trait red consistently associated with increased rate of diversification from Rabosky McCune 2010 TREE SI 3 SC Understanding the transition of tetrapod vertebrates from water to land Tiktaalik Fig 34 20 Acanthostega 4 Modification of existing structures for new purposes ears and feathers Feathers for display or warmth before flight Late Jurassic feathered dinosaur Fig 34 31 Bones of inner ear of modern mammals are derived from jaw joint of ancestors see also Fig 25 6 Recent discovery dinosaur feathers were colored display 5 Evolution of developmental genes phenotypic novelty Molecular homology genes with common ancestry controlling development top right Changes in timing and spatial pattern of expression change in phenotype E g Ubx suppresses leg development in flies but not shrimp Fig 25 22 6 Origin of novelties The vertebrate limb Are the fish fin and vertebrate limb homologous Very different anatomy yet Similar patterns of Hox gene expression Anatomic differences could be due to modification of timing duration of expression Shubin et al 2009 Nature 457 818 7 Evolution of hominins fossil evidence I Hominins split from common ancestor with chimps about 7Myr African origins diversity expands 4 2Myr Key features bipedalism smaller canines large brain later A ramidus neither chimp nor human see display in VLSB Australopiths probably paraphyletic with Homo Robust anthropoids Lucy Fig 34 40 8 Evolution of hominins fossil evidence II Homo key features increasing brain size reduced jaw lower sex dimorphism more terrestrial African origins H erectus europe 1 8Myr Indonesia Java man Extinct 200 Kya H floriensis 1M 12Kya Related to H erectus Neanderthals Europe and near east 200 24Kya Fig 34 40 9 Evolution of hominins fossil evidence III H floriensis Possibly persistent relative of H erectus or malformed H sapiens Exemplifies humans evolve as other species dwarfing of large mammals on islands eg Stegodon pygmy elephants huge lizards Varanus Putative tools 1Myr fossils to 12Kya overlapping H sapiens H floriensis Microcephalic H sapiens 10 Migration of H sapiens Out of Africa about 100Kya Rapid spread across Sth Asia to Australia central Asia One or 2 colonizations across Bering bridge during last ice age rapid spread to Sth America Polynesian migrations across Pacific are recent 1500 BC to 300 AD Hawaii 11 Modern humans related species hybridization or replacement Genetic evidence largely supports single origin outof Africa over independent origins from different populations of H erectus multi regional But did modern humans hybridize with or simply 12 replace neanderthals Paleogenomics Neanderthal v modern humans 60 38Kya bones of neanderthal sequenced compared to different human populations 2 3 neanderthal genes in eurasian papuan not africans Several genes eg skin pigmentation skeleton metabolism under recent selection in humans Refs Green et al 2010 Science 328 710 Gibbons 2010 Science 328 680 13 Denisovans another recent Homo 50 30Kya fossil Reich et al 2010 Nature 468 1053 4 5 2 5 440 270 Kya Neanderthals bottleneck Modern humans 14
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