Not the OP but I’m guessing that it’s because humans in Africa were isolated in thousands of communities/regions for hundreds of thousands of years and evolved separately. Meanwhile the diaspora outside of Africa spread via select communities in a much shorter time. Somewhat counterintuitive.
Humans haven’t been around long enough for that to happen. The most divergent groups outside Africa are that way because we met our distant relatives like Neanderthals, but it seems in our case they were just incompatible enough it didn’t add that much.
Africans esp the San have much more diversity than everyone else but IIRC it’s still remarkably low for our current population size.
Forgot to add this second main piece of evidence that modern humans are 'out of Africa': modern African populations have more genetic diversity. When populations migrate it's not a representative sample of all genes, but rather just limited groups, so you can find most diversity at/near the place where it evolved.
Not sure why downvoted, this is correct. The rest of the world was populated by small (i.e. less genetically diverse) groups who came "out of Africa". So "Africans are more diverse genetically than the inhabitants of the rest of the world combined"
there are "Larger Genetic Differences Within Africans Than Between Africans and Eurasians" "and the genetic diversity in Eurasians is largely a subset of that in Africans, supporting the out of Africa model of human evolution"
Humans have been living in Africa for as long as humans have existed--let's call that a round 300,000 years. The populations around where humanity first existed therefore reflects accumulated genetic diversity for all 300,000 years.
Let's say 100,000 years ago, a small group of humans left Africa for the other places of the world. That small group of humans represent a very small fraction of genetic diversity--it's effectively genetically identical. Assuming no more admixture over the millennia, the out-of-Africa humans will get more genetically diverse. But so are the original Africans, who also have the genetic diversity they started with--they're getting diverse no less quickly than the out-of-Africans, and since they started more diverse, the entire out-of-Africa can't ever catch up.
Real genetics is of course more complicated than this simple picture, but the basic principle holds that you find more diversity the closer you get to the origin.
It's also worth mentioning that if we assume that interbreeding didn't occur somewhat frequently then that means that non-African humans evolved from the same ancestors that the Neanderthals' and Denisovans evolved from, while most people in Africa evolved from another group or groups.
The earliest modern human remains found outside Africa date to about 200,000 years ago, yet almost all people born outside Africa are descendants of people migrating from Africa about 70,000-50,000 years ago. We don't really know what happened to the first waves of emigrants but we do know they didn't leave many traces. The traces we have found don't indicate hostility so the easiest explanation is that they simply lived alongside the Neanderthals and Denisovans and that the Neanderthals and Denisovans were more successful. Since we know there were interbreeding I find it very likely that those were isolated incicents, considering the human sexual drive. :)
This is an incredibly outdated view. There's no conflict between the strong multiregional hypothesis and SRO because the strong multiregional hypothesis is completely dead. To quote wiki [1]:
Outside of China, the Multiregional hypothesis has limited support, held only by a small number of paleoanthropologists.
What remains is largely a debate over when and how human evolution occurred within Africa. The classical view is that there's some singular population where H. sapiens evolved and spread from. In that view, we just have to sort out the chronologies and it'll work out. Opposing that is the relatively newer 'weak' or 'african' multiregionalism depending on who's talking. It argues that humans evolved as structured populations across Africa before leaving. It's a lot nicer conceptually and goes much farther to explaining the confusing apparent chronologies, but it requires revisiting a lot of prior work and assumptions. [2] is a good overview.
It's important to emphasize that these latter two aren't diametrically opposed and most paleoanthropologists are somewhere along the spectrum of both.
Looks like this adds to the evidence that our ancestors left Africa in a diaspora much, much earlier than had previously been thought, especially as this is far from their original continent.
> So one of the groups, either the "in Africa group" or the "out of Africa" group still should have the "old style brains" unless magically the changed happened in both groups at simultaneously.
Just because one group migrated earlier doesn't mean they were genetically isolated. Presumably there were subsequent migrations, counter-migrations (of large populations and smaller groups) and associated interbreeding between them.
There is one massive clue pointing to Africa: more genetic diversity there. This doesn't rule out interesting additions from other populations that left earlier than others, went further than we thought, etc; but it is the elephant in the room.
https://www.ncbi.nlm.nih.gov/pubmed/24984772
That is because Homo Sapiens "returned" to Africa after the invention of animal husbandry and agriculture. They out-competed and drove away many traditional hunter-gatherer tribes.
It is way more complicated than that. Even within Africa different groups moved around and exchanged with each other, then out of Africa there was intermingling along with returns to Africa and yet more migrations out of Africa.
They seriously talk about "African" as if it were a tight genetic grouping (like Icelanders or Ashkenazim) - Africa has the greatest human genetic diversity per distance of anywhere, as one would expect (diversity per distance is greatest near the point of origin).
Yep. There most likely were multiple waves of emigration from Africa. It's just that the most recent one is the one that made the largest impression in the gene pool.
Might also just be talking about specific geographical range. There is still a lot of debate on the time line and nature of the diaspora of modern homo sapiens.
Humans have not really had enough time as independent populations to diverge much. The north american land bridge disappeared ~14,500 years ago so only ~14,000 years as separate populations. African > Eurasia had regular exchanges as they where within relatively short walking distances.
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