Download Human Evolution

Human
Evolution
What were our
ancestors like?
Where did we evolve? Why big brains?
Relationships between populations?
Who are the closest living relatives
of humans? How do we know?
Bonobo
Chimp
Gorilla
Orang
Where are they now?
Orangs
Chimps
Gorillas
Bonobos
Early evidence: immunology
Mitochondrial gene phylogeny
Why might different genes yield
different phylogenies?
2
3
5
Why might different genes yield
different phylogenies?
What was the common ancestor
like?
Recent human phylogeny (best
guess)
Do we share genes with
Neanderthals or Homo erectus?
mtDNA from
Neanderthal
Relationships among contemporary
humans: mitochondrial DNA
Europe, Asia,
Australia
Asian / Australian
African
Interpretation of mitochondrial DNA
evidence
Did we have one female ancestor in the last
200,000 years?
Methods to determine ancestry:
coalescent
Common ancestry and genetic
markers
Genetic study of human traits
• Brain size – two loci of interest
– microcephalin (MCPH1)
– Abnormal spindle-like microcephaly
associated (ASPM)
– Selected?
ASPM and selection
Ka / Ks
McDonald-Kreitman test
fixed
polymorphic
replacements
19
6
silent
7
10
Evans et al 2004
Distribution of ASPM
Haplotype: 62kb
Mekel-Bobrov et al 2005.
Microcephalin and selection?
Ka / Ks
Wang and Su 2004.
Microcephalin distribution
Haplotype: 29 kb
Evans et al 2005
Microcephalin origins
Evans et al 2006
Relationships among human
populations: Fst
Evolution and races
• When did we stop being furry? How to
know? . . .
Evolution and races
Evolution and races: natural
selection on skin colour
Genetic Basis of Human Skin
Colour
• Partially known – one of ~6 loci identified
• Melanocortin 1 receptor (MC1R)
• Unusual pattern of sequence diversity
Human genetic diversity
Forces acting on human
populations
Sexual selection and humans
Diamond, 1992
Sexual selection and humans
Diamond, 1992
References
Currat, M. et al. 2006. Comment on “Ongoing adaptive evolution of ASPM” and
“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.
Wang, Y and Su, B. 2004. Human molecular genetics 13: 1131-1137.
Study questions
1.
2.
3.
4.
5.
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
human/chimp/gorilla relationships?
Is it accurate to say that humans evolved from chimps? Why
or why not?
In a study of Old World monkeys (Hayasaka et al. 1996) three
individual rhesus macaques that were studied did not form a
monophyletic group. Instead, one of the rhesus macaques
had mtDNA more closely related to Japanese and Taiwanese
macaques (which are different species). Give at least two
hypotheses explaining this.
Different ethnic groups within Africa are more genetically
distinct from each other than all other ethnic groups
combined. Explain why this might be the case.
Does the root of the human mtDNA tree in Africa imply that
there was a single female alive 200,000 years ago? Explain.
Study questions
6.
7.
8.
9.
10.
The human Y-chromosome tree appears younger than the
human mtDNA tree. Does this mean that females evolved
before males?
Would skin color be a good trait to use for human
phylogeny? Explain empirically (using data on the
relationships of human populations) and theoretically (the
role of traits under strong selection in phylogeny
reconstruction).
Are hypotheses of sexual selection shaping human anatomy
scientific?
Describe the role of each evolutionary force in human
evolution.
What do studies of chimps and bonobos tell us about human
nature? What are the limits of these studies?