mc2fool wrote:XFool wrote:mc2fool wrote:The perhaps more surprising ('twas to me at least) and less obvious case of genetic isolation is Africa. The Neanderthal genome project found that the Out-of-Africa migrations interbred with Neanderthals, and then kept going, the upshot of which is that everybody of the rest of the world populations today has 1-4% Neanderthal DNA (and a smattering of Denisovan) in them. However, not so for sub-Saharan African populations, in which Neanderthal DNA is generally absent.
I can't see why that should be "surprising", surely by present understanding it's pretty well required!
AFAIK, as a species "Neanderthals" evolved outside of Africa (although in turn their ancestors, like us, evolved in Africa) so it would only be subsequent 'Out of Africa' species that could have cross bred with them.
Yes, but that's besides my point. My comment was about what happened after that.
The lack of Neanderthal DNA in sub-Saharan African groups indicates that the descendants of the Out-of-Africa groups didn't -- in the 40,000 years following the last possible interbreeding with Neanderthals -- spread back into sub-Saharan Africa and promulgate their acquired Neanderthal DNA there. Some, sure, but not in any significant numbers at least.
That I find a little surprising, seeing they managed to spread to pretty much every other corner of the planet and, unlike the Americas and Australia, there was no significant geographical barrier that would have prevented some making a "return" over the last 40,000 years.
Are you sure? I have little real knowledge here but, again, Neanderthals evolved in Europe and spread to Asia, not back to Africa. Possibly the climate and the Sahara prevented intermixing with sub-Saharan African Homo Sapiens or even the return of significant numbers of Homo Sapiens who had interbred with Neanderthals? But if the movement of Sapiens was out of Africa and further afield, why would there be a significant population return (until historical times) when the territory was already occupied by Homo Sapiens? OK some small groups may have in time, but how could their Neanderthal genes really be important in a presumably then already significant African Sapien population - wouldn't they just get diluted away? - or a significant presence in the modern day African population? I just don't see it.
https://en.wikipedia.org/wiki/Neanderth ... _and_range
"No Neanderthal has ever been found outside Central to Western Eurasia, namely neither to the south of 30°N (Shuqba, Levant), nor east of 85°E (Denisova, Siberia).
...
Total Neanderthal effective population size has been estimated at close to 15,000 individuals (corresponding to a total population of roughly 150,000 individuals), living in small, isolated, inbred groups."
Then again, there are possibly other factors: https://en.wikipedia.org/wiki/Neanderth ... ern_humans