Have the experts converged on an answer to the question in the subject? I’ve heard a number of different estimates over the years, from 50,000 years ago to more than 100,000. I had a vague notion that they’d converged to around 65 or 70 K not too long ago, but perhaps I got the wrong idea.
Anyway, there’s a report on Science Daily that they’ve found 2 100,000 year-old partial human skulls in China. It says they’re “securely dated”, so it looks like the date is at least 100K and likely thousands of years earlier.
So do we have a new answer? Does this find throw lots of estimates into the dumpster?
The ancestors of the Aboriginal people of Australia appear to represent the first [or at least the oldest identified] population of genetically modern humans that left Africa.
We have them comfortably dated in Australia at nearly 50,000 years ago, with 60,000 years as a common working estimate. The genetic data indicates the initial population was the first here, and there was little later introduction in Australia, but a lot in New Guinea, until the first European settlement changed things quickly and catastrophically.
A date for them leaving Africa is hard to be precise about. Genetics suggest later in the 100-70,000 bracket than earlier.
The genetic data also suggests that, as they spread out of Africa, the ancestors of the Aboriginal people encountered other hominid occupants, notably the enigmatic Denisovians, and that they made sweet hominid love, and retain more Denisovian genetic material than other later dispersals from Africa, who have mainly Neanderthal admixture.
The Chinese skulls could be from one of several pre-modern Homo populations that have been identified. The genetics accentuate the biological gap, but in physical form, behaviour and culture they may have been a mile or a whisker different from the moderns.
At the moment every new genetic and skeletal find is complicating and adding nuance to the picture, rather than tying up and rationalising things into a simple story.
There was a wave of earlier Homo subspecies that first spread across Eurasia.
Before that, Homo Erectus seems to have also spread out from Africa, about 1.5 million years ago - the basis for Peking Man, Java Man. So already there was a fine tradition of very adaptable humanoids spreading to a wide variety of habitats.
There’s also the research that contends that about 70,000 years ago, there was a genetic “bottleneck”. The source population for modern humans was reduced to a small number (less than 1,000?). What caused this is debatable - was it a geological or climate event? Or was it that the group in question evolved a mutation (Speech? Consciousness? Abstract thinking?) that gave them such an overwhelming advantage that they simply pushed aside all competing populations and expanded rapidly?
As Banksiaman points out, by 60,000 years ago, give or take, they’d spread across the south of Asia to Australia. By 50,000 to 40,000 years ago, into Europe to displace the Neanderthals. The Australian migration suggests serious seagoing capability, something beyond drifting rafts. They obviously out-competed the locals in Europe, and presumably elsewhere.
Logic suggests (with no evidence) that a population bottleneck precedes dispersion. It’s less likely that a catastrophe reduced the population both inside and outside Africa after they had spread to a wide area of the world. More likely they recovered and then burst outward.
The linked article suggests the skulls from about 100,000 years agodisplay a mix of Neanderthal and modern human traits - which may say something about the breeding habits of proto-modern and earlier humans. It’s possible that earlier small groups of near-modern humans spread out from Africa, maybe, either physically or by passing on genetic material.
See this article linked by the OP’s article - Mystery human fossils put spotlight on China | ScienceDaily - suggests a residual population of humans with mixed characteristics survived in remote caves in China until almost 10,000 years ago. So maybe there was a population due to earlier mixing that was better suited to survive the competition with the real Homo Sapiens Sapiens.
I heard/read that there had been two different “out of Africa” migrations, and that the earliest wawe occupied the middle east and then died out, while the second wawe was the one that took over the world. Can’t give any link/cites. Just something I remember.
When we talk about “modern humans” we are usually referring to anatomically modern humans. The source pool for the majority of the genes of modern humans can be traced back a couple hundred thousand years ago to east africa. It’s thought one early group made it to the Levant and died out; a second migration just under 100K years ago is the “out of africa” population from which most of the gene pool of modern non-africans is derived.
That second group is thought to have interbred with earlier archaic hominins already out of africa.
Modern non-african populations have been recently (the work of Paabo and others) shown to have something like 1-4% of Neandertal genes. Some work has suggested that this part of the non-african genome was introgressed something like 50-75kya. Neandertal’s had bigger brains than we do, on average. Maybe we swiped some of those genes, although I’m not sure I got in on the deal. LOL
But there were other populations of archaic hominims who probably interbred with out of africa modern humans, including Denisovans and other Neandertal groups besides the ones studied so far.
The work you are looking at suggests that there was interbreeding as early as 100kya, which might move the date back a little for getting out of africa (or maybe the earliest groups did not die out completely), but is more or less in line with the general idea that anatomically modern humans arose in africa, and for populations which left africa, interbred with more archaic hominin lines.
If you look at modern non-african populations, you will see significant differences in the prevalence of many genes (more precisely, gene variants given the fact that “gene” is just a nickname for a chromosomal locus from which a particular genetic expression may derive) between (sub-saharan) african and non-african populations. For example, the penetration of MCPH1 Haplogroup D variant in non-african modern humans is substantially higher than in african populations. (I’m using “african” and “non-african” to refer to source pools for the gene variants.)
If confirmed, the find may rewrite the early migration story of our species, pushing back by about 50,000 years the time that Homo sapiens first ventured out of Africa.
I think the Y-chromosome mutation rate is fairly well calibrated by now. According to this site, B (ancestral to Pygmies and some other Africans) and CT (ancestral to everyone outside Africa) separated from each other 88,000 (±4500) years ago. C (ancestral to Australians, Apaches, etc.) and FT separated from each other 65,900 (±3200) years ago. Of course, there may have been earlier H.sapiens in Asia with a now-extinct haplogroup, which C males simply out-bred.
(FT is the haplogroup which expanded rapidly near Pakistan 48,000 years ago and has passed its Y-chromosome to a large majority of living males.)
And just to be complete, African populations of modern humans also interbred with non-sapiens, or archaic Homo populations that were still in Africa. There is evidence of this having happened both before and after the “Out of Africa” event. It’s beginning to look like wherever you have Homo, you basically have one population that interbreeds at least to some extent.
What’s kind of interesting is that, before all this genetic testing was available there were two competing hypothesis for how non-African populations evolved:
Out of Africa (we’re all recent emigrants from Africa, where recent means ~70K years ago)
Multi-regional (all current populations evolved from the existing, regional populations for hundreds of thousands of years)
In the early days of genetic testing, the OoA hypothesis was the hands-down winner. But now we’re at a stage where it’s more like 98% OoA + maybe 2% MR. A mixture of the two quantum states, so to speak.
