Hominds part 2 Out of Africa: DNA clocks Multiregionalism: the Neanderthal within us all Bipedalism.
Transcript of Hominds part 2 Out of Africa: DNA clocks Multiregionalism: the Neanderthal within us all Bipedalism.
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
• mT DNA does not undergo recombination; only mutation
• 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
DNA clocks
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
Neanderthals+ multiregionalism
• Major skull differences:
• Neanderthals have:– Longer, lower occipital
bun– 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 Neanderthal-
homo 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 recombination?
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 hunting
• 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