1Bio1B Evolution 12Last lecture: Fossil recordFossil record - significance & interpretationExtinction -Background extinction rates and the “big 5” mass extinctionThe “K/T” boundary - asteroid hypothesis; dinosaur extinctions, radiationof mammalsAre humans causing the 6th mass extinction?TodayMacro-evolution (cont.)Species selectionTransitional forms - tetrapods, birds: “exaptation”Evolution of developmental programs - eg. vertebrate limbsHuman evolutionEvolutionary origins of Homo sapiens: fossils & molecular evidence2Are we the cause of the 6th massextinction? (Barnosky et al. Nature 2011)3Macro-evolution: Species selectionEvolution of particular trait (red)consistently associated withincreased rate of diversification (fromRabosky & McCune 2010 TREE)BUT -diversificationrate (S-E) -higher in SI(purple) thanSC (blue)E.g. self incompatibility (SI) in hermaphroditic plants isoften disdadvantageous within species compared toself-compatibility (SC)E E Goldberg et al.Science 2010;330:493-495SISC4Understanding the transition of tetrapodvertebrates from water to landFig 34.20TiktaalikAcanthostega5Modification of existing structures for newpurposes: ears and feathersFig. 34.31. Bones of inner ear ofmodern mammals are derived fromjaw joint of ancestors (see also Fig.25.6LateJurassicfeathereddinosaurFeathers:for displayor warmthbeforeflight?Recent discovery:dinosaur featherswere colored -display?6Evolution ofdevelopmental genes=> phenotypic novelty• Molecular homology: geneswith common ancestrycontrolling development (topright)• Changes in timing andspatial pattern of expression=> change in phenotype• E.g Ubx suppresses legdevelopment in flies, but notshrimpFig. 25.227Origin of novelties:The vertebrate limb• Are the fish “fin” and vertebrate“limb” homologous?• Very different anatomy, yet…• Similar patterns of Hox geneexpression• Anatomic differences could be dueto modification of timing/duration ofexpression?Shubin etal. 2009Nature457:8188Evolution ofhominins: fossilevidence IFig. 34.40• Hominins split fromcommon ancestor withchimps about 7Myr;African origins, diversityexpands 4-2Myr• Key features: bipedalism,smaller canines (largebrain later)• A. ramidus - neitherchimp nor human - seedisplay in VLSB• “Australopiths” probablyparaphyletic with Homo“Lucy”Robustanthropoids9Evolution of hominins: fossilevidence IIFig. 34.40• Homo - key features:increasing brain size,reduced jaw, lower sexdimorphism, moreterrestrial• African origins; H. erectus-> europe >1.8Myr ->Indonesia (“Java man”).Extinct 200 Kya?• H. floriensis - >1M? -12Kya. Related to H.erectus?• Neanderthals - Europeand near east, 200-24Kya?10Evolution ofhominins: fossilevidence IIIH. floriensis• Possibly persistentrelative of H. erectus [ormalformed H. sapiens?]• Exemplifies humansevolve as other species:dwarfing of largemammals on islands -eg. Stegodon “pygmyelephants & hugelizards! (Varanus)• Putative tools >1Myr,fossils to 12Kya -overlapping H. sapiensH. floriensisMicrocephalicH. sapiens11Migration of H. sapiens• Out of Africa - about100Kya• Rapid spread across SthAsia to Australia & centralAsia• One or 2 colonizationsacross Bering bridgeduring last ice age ->rapid spread to SthAmerica• Polynesian migrationsacross Pacific are recent:1500 BC to 300 AD(Hawaii)12Modern humans &related species -hybridization orreplacement?Genetic evidence largelysupports single origin & “out-of- Africa” over independentorigins from differentpopulations of H. erectus(multi-regional).But did modern humanshybridize with, or simplyreplace neanderthals?13Paleogenomics: Neanderthal v modern humans• 60-38Kya bones of neanderthalsequenced - compared to differenthuman populations• 2-3% neanderthal genes ineurasian-papuan, not africans• Several genes - eg skin &pigmentation, skeleton, metabolismunder recent selection in humans• Refs: Green et al. 2010 Science 328:710,Gibbons 2010 Science 328:68014‘Denisovans’ - anotherrecent HomoNeanderthals(bottleneck?)Modernhumans440-270 Kya2.5%4-5%Reich et al. 2010 Nature
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