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