New Type of Ancient Human Found—Descendants Live Today?

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The distance isn't important per se. What is important is that we have a single population, whose status as a single population is maintained by regular and frequent interbreeding of neighboring groups (what we've been calling the smaller populations).

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I'm afraid I'm having trouble understanding what your model is here. If there had been a single population with some regional diversification and a constant flow of genes between neighbors, how did 95+% of Scandinavian alleles come to be of African origin, while virtually no African alleles are of Scandinavian origin? What kind of gene flow could possibly produce that situation, short of substantial numbers of people moving (on average, and over many generations) from Africa toward Scandinavia?

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While it is true that the Human population can be split quite easily as "those who never left Africa" and "everyone else", I think what Jon's shooting for is: "They are all human".

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The difference between the most "African" African and the most "Swedish" Swede really isn't that different at all.

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Scientists have been very successful at picking out and labeling differences between various populations, largely because the differences give us information. Noting the 99% of genes that are identical and provide no usable information about population dynamics or movements, doesn't really make for good publishing material.

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True, but completely irrelevant to distinguishing between OoH and MR models.

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Further I think Jon is trying to point out that in the pre-historical past, the historical past and the present, humans are particularly good at getting around and getting it on.

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It's hard to find anyone in a modern society who is ethnically pure. But that's not just something from a modern society. I'm sure if you were in ancient Rome, you'd likely meet someone who's father was a Gaul and who's mother came from Egypt or whatever.

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Also true, but again, I don't see the relevance.

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The lack of differences between populations, and our ability to flow genes between groups which are relatively isolated, means that it is extremely unlikely in our current situation that we'll see a split of humanity into two distinct species.

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Since the populations we're discussing (African archaic Homo, Neandertals and Denisovans) were more isolated than modern populations and far more diverged genetically, again, I don't see what this has to do with subject at hand.

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Indeed; and I would say unlikely even in past times during which pre-sapiens made the transition to sapiens. We have yet to find any modern population of people that has been isolated long enough to speciate, and the on-off isolation offered by oscillating geographical and environmental factors does not seem to provide sufficient time for speciation. It seems reasonable that the factors that have allowed people the world over to maintain their identity as members of the same human speciesincluding and especially those natural ones from pre-technological and pre-exploration timeshave been in effect since the erectus expansion.

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Since the pre-sapiens populations were far more diverged genetically than any modern populations, your confidence in the similarity in the processes involved is misplaced.

Jon, since you haven't answered my question, I'm going to repeat it: "If there had been a single population with some regional diversification and a constant flow of genes between neighbors, how did 95+% of Scandinavian alleles come to be of African origin, while virtually no African alleles are of Scandinavian origin? What kind of gene flow could possibly produce that situation, short of substantial numbers of people moving (on average, and over many generations) from Africa toward Scandinavia? "You seem to think there's a model based on gene flow, without migration, that could explain this most obvious feature of human genetics. What is it?

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And isn't that, pretty much, what the MH model is saying?

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No, the MH model says that modern humans largely evolved as a dispersed population, with gene flow throughout.

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But it seems to me that the OOA model specifically excludes that assimilation.

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At this point we're getting into a purely semantic question, but that's not the way I've understood the term OoA to be used, and I've tried to pay attention (and even contribute) to the genetic studies on this issue. My understanding is better reflected in this quotation from Chris Stringer (from Nature, in 2003):"There are two broad theories about the origins of H. sapiens. A few researchers still support a version of the 'multiregional' hypothesis, arguing that the anatomical features of modern humans arose in geographically widespread hominid populations throughout the Pleistocene epoch (which lasted from around 1.8 million to some 12,000 years ago)6. But most now espouse a version of the 'out of Africa' model, although there are differences of opinion over the complexity of the processes of origin and dispersal, and over the amount of mixing that might subsequently have occurred with archaic (non-modern) humans outside of Africa2, 7".

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Not when the 'Paleo-African' groups were the largest, most dense, and central groups of the world population. Then the dominance is entirely consistent and expected given either the MH or OOA model. Genetic traits of the central, large, denser groups of a population will naturally dominate the population as a whole whether through hybridization or OOA-type migration. Dominance of African alleles does not necessarily support the OOA model anymore than it supports an alternative model.

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But does this constitute a plausible model? If you're relying solely on the greater pool of chromosomes in sub-Saharan Africa to explain the disparity in where alleles arose, what kind of population structure are you going to have to posit? If you just think about a simple model with two populations (say Europe and Africa), the minimum disparity in population sizes will be with large gene flow rates between them. In that case, for 95% of European alleles to originate in Africa, 95% of the population also had to reside there. But the ancestral effective population size of humans is only ~15,000, for the entire worldwide population. That means you've got something like 700 individuals living in all of Europe. If you factor in restrictions to gene flow and the dilution from the lengthy pipeline alleles had to diffuse through to get from one region to the other, and account for the rest of Eurasia, the actual population would have had to be even smaller. That's simply not a plausible size to be maintaining genetic continuity with Asia and Africa. (Indeed, it's pretty precarious as a population for avoiding local extinction.)There's also the question of when this gene flow is supposed to have been happening. MRH assumes long-term, ongoing gene flow for well over a million years. What the Neandertal and Denisovan genomes show, however, is that there was a great deal of genetic isolation of these populations from the ancestors of modern humans, up to as recently as 40,000 years ago -- and yet you're arguing that the relatedness of modern Europeans and Africans results from gene flow between them. When were the genes flowing?

My description of multiregionalism and the one you quoted from Wikipedia are completely consistent.

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I've already addressed several of your points earlier on in the thread in replies to other members, especially Bluejay.

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No, you haven't. I've looked at all of your posts in this thread, and nowhere do you address the size of non-African populations required by your model or the timing of the proposed gene flow (as in saying when it happened, not vague comments about off-and-on migration). Those were the points I made in my points, and you have not addressed them.

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I will add, however, that the 95% needn't happen over night. Given time and a continued disparity in population density, size, and centrality, one populations genetic information can certainly swamp out the information from another population, without super exoduses taking place from the former to the latter.

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Certainly. Now propose a reasonable model for that happening in the development of humans, given what is known about human genetics. Edited by sfs, : No reason given.

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I've never heard the term "selective sweep" before. Thanks for the new education!

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Still, this isn't a genome full of "irrelevant" alleles spreading through a population by hybridization: this is a single advantageous allele, plus a few "irrelevant" alleles neighboring it on a chromosome, being spread with the help of natural selection.

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You can't seriously say that genetic linkage accounts for 95%+ homology. The Wikipedia article you linked to says there is evidence for selective sweeps on 6 out of 23 human chromosomes. And these don't include an entire chromosome, but just small regions of chromosomes associated with single genes.

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There is evidence for many more selective sweeps than are mentioned in the Wikipedia article (see here, for example). They still constitute a small fraction of the genome, however. Moreover, they are almost always confined to one geographic region, and there is no evidence that the selected alleles arose preferentially in Africa. (In fact, the largest class of well-studied selective sweeps involves those for light skin pigmentation, whose alleles are typically absent within Africa.)

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And on what grounds do you make this conclusion?

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On the same grounds that almost all geneticists reached the same conclusion: the weight all of the evidence. No plausible MR model could be found that could explain the available data on patterns of human genetic diversity, while a range of OoA models could. It remained an open question whether there had been any introgression from archaic populations, with a number of pieces of equivocal evidence suggesting that there had been a modest amount. That question seems to have been settled by the recent Neandertal and Denisovan sequencing (assuming the analysis is more or less correct, which I think very likely, given who's done it), but otherwise the picture hasn't changed.

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Huh? I'm not here for that.

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If not that, then what? Unreasonable models, or models inconsistent with what's known about human genetics?

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You want actual numbers?

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Yup. It was models with actual numbers -- sometimes crude ones, to be sure -- that convinced the genetics world that the MRH was untenable. If you wish to overturn that conclusion, as you seem to, you have to grapple with those numbers.Edited by sfs, : hit send too soon

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But there are; they've been published and republished. Why ignore them?

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Which models do you mean? Every even moderately detailed demographic model of human genetic variation that I've seen has been based on some version of OoA.

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And, there are migrations that are better documented than those: Celtic peoples used to live all across Europe. In the first few centuries AD, the Germanic peoples migrated across Europe from the North and displaced the Celts. A few hundred years later, the Slavic peoples also migrated into Eastern and Southern Europe from Siberia or Ukraine (there are competing theories). And, don't forget the Vikings.

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How about the Moors? They invaded Spain from northern Africa in the Middle Ages, and their descendants are still there.

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How about the Romani? They live all over Europe.

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In the 1700's and 1800's, the Russians expanded northward, eastward and westward, taking over Murmansk, Siberia and parts of the Baltic.

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That's just off the top of my head, and I'm not even a historian. If I were given time, I'm sure I could list dozens more large migration events like these.

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Add Huns, Mongols, Tatars, Magyars, Turks, Aryans in India, the Sea Peoples, the Polynesians and (one of the biggest) the Bantu speakers in Africa.

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Speciation isn't really even an issue here: divergence has clearly happened, as evidenced by haplogroup distribution among different regional populations, and by the occasional observation that some races respond differently to medications, and by features like Coyote mentioned (the characteristic incisor shape of Asians). True, it's doubtful that regional populations of humans even warrant subspecies designation, but this is pretty immaterial to the whole point.

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It's worth noting that the human population seems to have been much larger over the last 50,000 years or so than it was during the preceding lengthy period when the MR development was supposed to have been taking place. The recent period is also much shorter.