A while back I asked about the Toba eruption 70,000 years ago, which brought the total human population down to about 10,000 individuals - obviously wiping out a large amount of the human genetic pool.
What I wonder is; what if this event hadn’t occurred - what would be the consequences today?
From what I’ve gathered this event seemed to spur the divergences of different racial traits;
“…this in turn accelerated differentiation of the reduced human population. Therefore, Toba may have caused modern races to differentiate abruptly only 70,000 years ago, rather than gradually over one million years.[24]”
(from the wiki).
I’m not really sure how this works - wouldn’t fewer humans lead to fewer differentiations? I’m also assuming that a great number of humans, and genetic material, would lead to less genetic diseases in the species. After all, anyone who’s thought about their ancestors quickly realises that the number of possible ancestors soon outnumbers the number of humans on Earth, making inbreeding clear.
A rider question; would there be any other consequences? Would the greater population have necessitated the development of agriculture and cities earlier, making our civilisation now several thousands of years more advanced?
I’ve put this in GQ, as I hope there’s enough known about genetics and prehistory for some educated guesses, but I realise there isn’t a 100% factual answer.
At the time Toba erupted, humans had expanded out of Africa along the southern shoreline of Asia, from the Arabian peninsula to southern China. Toba deposited humongous amounts of ash on the Indian subcontinent, making it uninhabitable. So humanity was divided into three geographically isolated populations located in Africa, southwest Asia, and southeast Asia. Due to the founder effects mentioned above, these three populations were the origin of the main divisions of humanity.
Ah, I understand now, the founder effect. Thanks for the replies.
After everyone in what was to become India was wiped out the vanguard of the migration out of Africa was totally isolated, with no new influx of new genetic material from Africa, which lead to those populations developing different traits than their cousins elsewhere.
So without the eruption, this founder effect would have been much reduced, if present at all, as humanity would be able to continuously migrate across the subcontinent. So, would we look far more similar to each other today without Toba?
I don’t know about this. Most sources I’m familiar with put the Toba eruption before the migration of modern humans out of Africa. Wmfellow’s cite seems to suggest this, too, although it’s a bit vague.
I was rather curious about this and googled about. For what it is worth, it seems a GQ type response would be “too much noise around dating” re genetic clock estimates to know precisely. Seems as if his read is not excluded, but most of the articles I pulled up seemed to imply that no one outside of Africa survived is the base assumption.
Yes. That’s also supported by the fossil evidence, of which there is none outside of Africa beyond about 42k years ago. That is excluding those found in the Middle East much earlier, but which are thought to have been from a population that either went extinct, or returned to Africa.
I was basing my answer on this site here: Journey of Mankind. That site dates the exit from Africa at about 85,000 years ago, which may not be in accord with the ideas of other paleoanthropologists. Which is not too surprising, since such scientists rarely agree on anything in their field of study.
I also simplified the origins of Europeans, but that’s because I was doing it from memory, which is not perfect. To get a better idea of that, see the 65,000-52,000 years ago subpage and read the sidebar.
A population of 10,000 is not small enough for inbreeding to be a serious genetic problem. Cheetah is a classic example of excessive inbreeding: it’s estimated one of the subspecies encountered a bottleneck smaller than 7 individuals!
I think “greater population necessitates agriculture” puts the cart before the horse. (Clear, I think, if you admit agriculture takes more than a generation to “develop.”)
I think some researchers still accept the possibility of early H. sapiens interbreeding, in Asia and Australia, with earlier hominids (e.g. H. erectus). This is not incompatible with the recency of “Mitochondrial Eve” and “Y-chromosome Adam” since those chains represent only part of human genes. (Among your 1 million gggggggggggggggggg-grandparents, only two contribute to your “Eve” or “Adam” signature.)
While paleoanthropologists do squabble a lot, I think this guy is a real outlier. He puts humans in Australia at ~70k years ago. That’s at least 20k years earlier than is generally accepted. And that data is from 2003-- a bit out of date by today’s standards/