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Human Evolution Who are the closest living relatives of humans? How do we know? Human Evolution Bonobo Chimp Gorilla Orang What were our ancestors like? Where did we evolve? Why big brains? Relationships between populations? Where are they now? Early evidence: immunology Orangs Gorillas Chimps Bonobos 1 Why might different genes yield Mitochondrial gene phylogeny different phylogenies? 23 5 Why might different genes yield What was the common ancestor different phylogenies? like? 2 Recent human phylogeny (best Do we share genes with guess) Neanderthals or Homo erectus? mtDNA from Neanderthal Relationships among contemporary Interpretation of mitochondrial DNA humans: mitochondrial DNA evidence Europe, Asia, Did we have one female ancestor in the last Australia 200,000 years? Asian / Australian African 3 Methods to determine ancestry: Common ancestry and genetic coalescent markers Genetic study of human traits ASPM and selection • Brain size – two loci of interest Ka / Ks – microcephalin (MCPH1) – Abnormal spindle-like microcephaly associated (ASPM) – Selected? McDonald-Kreitman test fixed polymorphic replacements 19 6 silent 7 10 Evans et al 2004 4 Distribution of ASPM Microcephalin and selection? Ka / Ks Haplotype: 62kb Wang and Su 2004. Mekel-Bobrov et al 2005. Microcephalin distribution Microcephalin origins Haplotype: 29 kb Evans et al 2005 Evans et al 2006 5 Relationships among human Evolution and races populations: Fst • When did we stop being furry? How to know? . Evolution and races: natural Evolution and races selection on skin colour 6 Genetic Basis of Human Skin Human genetic diversity Colour • Partially known – one of ~6 loci identified • Melanocortin 1 receptor (MC1R) • Unusual pattern of sequence diversity Forces acting on human Sexual selection and humans populations Diamond, 1992 7 References Currat, M. et al. 2006. Comment on “Ongoing adaptive evolution of ASPM” and Sexual selection and humans “Microcephalin, a gene regulating brain size”. Science 313:172a. Diamond, J. 1992. The third chimpanzee. HarperCollins. Evans, P. D. et al. 2004. Adaptive evolution of ASPM, a major determinant of cerebral cortical size in humans. Human molecular genetics 13:489-494. Evans, P. D. et al. 2005. Microcephalin, a gene regulating brain size, continues to evolve adaptively in humans. Science 309:1717-1720. Evans, P. D. et al. 2006. Evidence that the adaptive allele of the brain size gene microcephalin introgressed into Homo sapiens from an archaic Homo lineage. PNAS 103:18178-18183. Jablonski, N. G. and Chapin, G. 2000. The evolution of human skin coloration. Journal of human evolution 39: 57-106. Kittler, R. et al. 2003. Molecular evolution of Pediculus humanus and the origin of clothing. Current Biology 13:1414-1417. McKee, J. K. et al. 2005. Undertanding human evolution (5th ed.) Pearson Prentice Hall. Mekel-Bobrov, N. et al. 2005. Ongoing adaptive evolution of ASPM, a brain size determinant in Homo sapiens. Science 309: 1720-1722. Rosenberg, N. A. et al. 2002. Genetic structure of human populations Science 298: 2381-2385. Templeton, A. 2002. Out of Africa again and again. Nature 416:45-51. Varki and Altheide. 2005. Comparing the human and chimpanzee genomes: searching for needles in a haystack. Genome research 15:1746-1758. Diamond, 1992 Wang, Y and Su, B. 2004. Human molecular genetics 13: 1131-1137. Study questions Study questions 1. Explain lineage sorting. Why is it more likely to occur with relatively short times between speciation events? How might this explain different results for different genes for the 6. The human Y-chromosome tree appears younger than the human/chimp/gorilla relationships? human mtDNA tree. Does this mean that females evolved 2. Is it accurate to say that humans evolved from chimps? Why before males? or why not? 7. Would skin color be a good trait to use for human phylogeny? Explain empirically (using data on the 3. In a study of Old World monkeys (Hayasaka et al. 1996) three relationships of human populations) and theoretically (the individual rhesus macaques that were studied did not form a role of traits under strong selection in phylogeny monophyletic group. Instead, one of the rhesus macaques reconstruction). had mtDNA more closely related to Japanese and Taiwanese 8. Are hypotheses of sexual selection shaping human anatomy macaques (which are different species). Give at least two scientific? hypotheses explaining this. 9. Describe the role of each evolutionary force in human 4. Different ethnic groups within Africa are more genetically evolution. distinct from each other than all other ethnic groups 10. What do studies of chimps and bonobos tell us about human combined. Explain why this might be the case. nature? What are the limits of these studies? 5. Does the root of the human mtDNA tree in Africa imply that there was a single female alive 200,000 years ago? Explain. 8.
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