New Type of Ancient Human Found—Descendants Live Today?

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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.)

Hi, CS. Sure, I'm always open to discussing things with someone who wants to discuss them.----- I tend to agree more with Taq's mechanistic approach. It seems silly to me to formulate a theory about biology---a field in which essentially all data sets are messy---so that it can't tolerate any deviance from 100% purity.This seems like what the new MR-proponents are doing: they're arguing that any deviance from the most stringent interpretation of OoA is vindication of MR.----- What's happened here is a kind of distillation of the two theories into pure principles. But, neither one was really a "pure principle" to begin with.MR was specifically the idea that H. erectus, Neanderthal and Africans were all the same species, and that each population evolved in partial isolation into the regional varieties of human that we see today (i.e. African, European and Asian), although they were not isolated enough to break the general continuity of the species that we see today.MR has been resurrected in principle because a trace amount of admixture was found. This admixture doesn't actually explain any of the evidence that MR was originally proposed to explain (e.g., the morphological features shared by H. erectus and modern Asians), and doesn't really demonstrate what the original MR proposed.So basically it's a redefinition of MR as any model proposing that somebody, somewhere, has a non-African ancestor; which accordingly redefines OoA as any model proposing that nobody, anywhere has a non-African ancestor.I don't think this is a fair interpretation of either theory. And, I think it's certainly abnormal to propose that a scientific theory included a universal negative statement as one of its core claims.But, in the end, we're just debating about what to call the paradigm, rather than debating the principles and concepts involved, so it's not something I'm going to get rabid about.

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-Bluejay (a.k.a. Mantis, Thylacosmilus)Darwin loves you.

Hi, Jon. I don't think anybody assumes that migration is the only explanation: we all conclude that it's by far the best explanation. That's all science ever does.Theoretically, selective sweeps and passive diffusion could very well cause a population to reach 95% homology with a different population. I'll grant you that theoretical possibility. But, realistically, given our actual observations of hybrid populations and selective sweeps, it's highly dubious, at best.

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-Bluejay (a.k.a. Mantis, Thylacosmilus)Darwin loves you.

It is also important to keep the big question in mind when discussing the topic. The big question is how did so much African DNA spread across the globe. What was the main cause of this observation. I won't argue at all that some of our DNA came from Neanderthals and possibly from other non-modern human species, but the vast majority came from Africa quite recently.To use an analogy, we often focus on one aspect of natural selection to describe the whole. We tend to say that beneficial mutations are passed on at a higher rate until they reach fixation. However, some neutral mutations do the same, just at a different rate. Do neutral mutations somehow negate the effects of positive selection? Not at all. More importantly, we are also focused on a big question: How do species adapt to their environment. That is why we stress positive selection as the major mechanism, even though other mechanisms are at work in the background. The same for the OoA and MH mechanisms.

One factor I don't recall seeing in the above posts which may help to account for the high rate of gene flow from Africa is culture and technology.With a more advanced culture and better technology than among those folks on the peripheries, the folks moving out of Africa could probably have supported larger populations. This would have enhanced their gene flow.I did a dissertation which included this type of approach, although not dealing with the early hominids vs. modern humans.The problem with this is that technology can spread from one group to another, helping to eliminate the disparity. But to the degree that the brains were different between the folks moving from Africa and the older groups in the peripheries, they may not have been able to adopt some of the culture and technology of the incoming out of Africa folks.This general theme was explored in the Clan of the Cave Bear series, where Neanderthals were portrayed as being unable to quickly adopt new ideas. Though fiction, this illustrates one very real possibility by which the OoA folks could have had an advantage as they spread and absorbed earlier populations.

Are presently isolated peoples not human?Jon

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Check out No webpage found at provided URL: Apollo's Temple!
Ignorance is temporary; you should be able to overcome it. - nwr

And on what grounds do you make this conclusion?Jon

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Check out No webpage found at provided URL: Apollo's Temple!
Ignorance is temporary; you should be able to overcome it. - nwr

Huh? I'm not here for that. You want actual numbers?Jon

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Check out No webpage found at provided URL: Apollo's Temple!
Ignorance is temporary; you should be able to overcome it. - nwr

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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

Hi, Jon. I think I've already described the grounds on which I, personally, make this conclusion. Remember that stuff about "no non-migration explanation has yet been demonstrated to have caused such evidence as we see" and "there are numerous cases in which immigration models, with or without genetic admixture, have caused population turnover"?Remember that stuff?I think that was pretty good stuff, but that doesn't mean I want to just repeat it all over again.

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-Bluejay (a.k.a. Mantis, Thylacosmilus)Darwin loves you.

Are they as divergent from other humans as Africans, Neanderthals, and the recent Denisova find?

The information you're requesting is far beyond me to present; people have written entire books on these matters.Jon

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Check out No webpage found at provided URL: Apollo's Temple!
Ignorance is temporary; you should be able to overcome it. - nwr

I don't entirely understand the question. What do you want me to compare Africans, Neanderthals, etc. to? One another? Modern humans?Jon

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Check out No webpage found at provided URL: Apollo's Temple!
Ignorance is temporary; you should be able to overcome it. - nwr