1Bio1B Evolution 12Last lecture: Fossil record (cont.)Mass extinctions - the “K/T” boundary - asteriod hypothesis; dinosaue extinctions,radiation of mammalsTransitional forms - tetrapods, birds: “exaptation”Evolution of developmental programs - “deep homology”; eg. vertebrate limbs,animal eyesTodayEvolutionary origins of Homo sapiens: fossils & molecularevidenceRecent evolution of humans - eg lactose tolerance in adultsEvolutionary medicine: basic concepts and examplesPathogen evolution - eg. HIV evolution within single hostsMetabolic diseases: “thrifty gene hypothesis” & obesity, type2 diabetesFurther courses in Evolution at UC Berkeley2Evolution 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”Robustanthropoids3Evolution ofhominins: fossilevidence IIFig. 34.40• Homo - key features:increasing brain size,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 andnear east, 200-24Kya?4Evolution 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. sapiens5Migration 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 1000 AD(New Zealand)6Modern 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?7Recent evolution inhumans - lactosetolerance in adults• Tolerance of lactosein adults is a recentlyevolved trait inhumans• Molecular analysesshow independentorigins from differentmutations in lactasegene in Africa and NthEurope• The mutations areabsent from fossilneolithic farmers 6-5Kya• Lactose intolerance isthe norm, not adisease!8Principles of Evolutionary Medicine(see Zimmer pdf; also new course in IB - Tom Carlson)• Understanding evolutionary basis of diseaserisk can improve diagnosis and prevention• Variation in human phenotypes results fromgenetic variation and environmentalinfluences on development• Selection operates to maximize (inclusive)fitness, not health and longevity. This canresult in trade-offs9Rapid evolution of pathogens: HIV(an RNA virus) within hostsFrom Zimmer 200910Evolutionary mismatches & constraintssee Zimmer pdf• “Thrifty genes hypothesis”– Native American and others selected for efficientmetabolism because of history of famine => with“obesogenic” food types very prone to obesity + type IIdiabetes• Rapid life history evolution, aging and late-onsetdiseases– Tradeoff between selection for genes important pre-reproduction (growth) and post-reproduction (repair)• Hygiene hypothesis - reduced exposure topathogens in children => increase in autoimmunedisease (athsma etc)?• Evolutionary constraints: appendix, detachedretina, small birth canal cf, brain size,
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