African Exodus

123-117 thousand years ago

Our genus, Homo, left Africa by 1.8 million years ago. There may have been another Out-Of Africa migration around 200,000 years ago that introduced early Homo sapiens mitochondrial DNA into the Neanderthal gene pool. This early migration didn’t lead to major evolutionary change, however. Other Neanderthal genes (i.e. nuclear rather than mitochondrial DNA) show no evidence of it.

More consequential was another Out Of Africa migration by Homo sapiens around 120,000 years ago. This skull dates back to then.
Skhul 5 was found back in 1935, in Israel, on the slopes of Mount Carmel, buried together with a boar mandible. It looked for a long time like the skull came late in the day, and might represent a transition from Neanderthals to Homo sapiens. But now that date has been moved back, thanks to the development of new dating techniques (thermoluminescence, electron spin resonance) that finally broke the 40,000 year limit for Carbon 14. Skhul 5 now looks like a representative of an early movement of Homo sapiens out of Africa. But the skull also has some Neandethal-like features (check out the “Neanderthal bun” at the back of the skull) and could have hybrid ancestry.

Until recently it looked like this and other very early Homo sapiens outside Africa were a side branch that left no descendants – think Leif Erickson, not Columbus – with the real move coming later. But recently there has been a recalibration of DNA mutation rates that suggests that the split between African and non-African branches of H. sapiens happened closer to 100,000 years ago than 50,000 years ago. And there have been discoveries of stone tools with African affinities in the Arabian Peninsula, in the United Arab Emirates (Jebel Faya, 125 kya) and Oman (106 kya). It may be that when Homo sapiens left Africa 125,000 years ago (perhaps across the Red Sea to Arabia, rather than across the Sinai), they spent a long time isolated in a corner of Southwest Asia before much later expanding more widely.


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