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Hominds part 2
• Out of Africa: DNA clocks
• Multiregionalism: the Neanderthal within us all
• Bipedalism
DNA clocks
• DNA can vary because of:
– Mutation (random copying errors which
accrue with time)
– Recombination (1/2 of each parent’s
DNA mixed to make child)
DNA clocks: mitochondrial DNA
• A portion of our DNA comes only from our
mothers, and experiences ONLY mutation
DNA clocks
• mT DNA does not undergo recombination; only
• mT DNA is thought to mutate at a constant rate
• Small mutations in DNA through time; 2-4% per
million years
• Calibrated against dateable fossils
– Difference between 2 organisms
• Last common ancestor between humans and chimps:
350,000 generations ago, or about 5-7 million years
Out of Africa
• mT DNA of thousands of humans all point
to a last common maternal ancestor
200,000- 120,000 years ago -- very recent!
• Furthermore:
– Highest gene diversity in Africa
– Asian, European genes present in African pools
but not others
– + statistical modeling -->
• Homo sapiens did not mix genetically
with homo erectus.
Out of Africa
• Neanderthal mT DNA:
– Very different from modern humans
– Hard to reconcile difference with
possible presence of some
Neanderthal ancestry in modern
homo sapiens
• Major skull differences:
• Neanderthals have:
– Longer, lower occipital
– Big retromolar gap
– Almost no chin
– Strong browridge
– Sloping face
Early modern homo sapiens in
Europe after Neanderthals were gone
• Hybrid child
• Adult skeletons with a range of brow ridges,
retromolar gaps, occipital bun sizes
• Simple explanation: some Neanderthalhomo sapiens interbreeding
• Geneticist response: convergent evolution
(requires puropose for retromolar gap, chin,
and browridge)
Other possibilities:
• Hybrids didn’t survive for some reason
• Hybrids DID survive, but we just not
looking at the right part of the genome yet.
• Y-chromosome data: recent African origin
• How to use rest of genome subjected to
Why bipedalism?
Less exposure to sun
Easier to carry children, food
Easier to reach food in trees
Less energetically expensive
– Quadupedal knuckle-walking: ~35% more
energy than walking on 2 legs
• Dense forests: < 1 mile/day to gather food
• Savannahs: 6-8 miles/day to gather food
Bipedal movement freed up energy for
brain development
Brain development supported
• Higher calorie diet from meat allowed more
brain development
– C and N isotopes in bone give information
about proportion of meat in diet
– Neanderthal diet: almost all protein from meat