New Type of Ancient Human Found—Descendants Live Today?

How did European genes come to dominate the gene pool in North America, and why did the previous dominant indigenous DNA decline in number? Was it due to gene flow between static populations or was it due to migration?How would DNA that evolved on the open savannas of Africa come to dominate very different habitats? The MH theory would argue that African lineages would make up a much smaller proportion of local variation with locally evolved DNA being dominant. That is not what we see. We see something akin to the appearance of European DNA in North America.

However, Paleo-African groups were not the densest population in Asia. Paleo-Asian groups were. If I was an early human in Asia what was the probability that I would mate with someone within the Asian population compared to the African population? I would tend to think that the odds were stronly in favor of a fellow Asian, no?The MH model requires dilution of the African genome as it is transmitted across large distances. As the Paleo-African genome is transmitted across these distances it is diluted by local variation. The density or size of the Paleo-African population is limited by the bottleneck of gene flow between populations. Geography between the continents demands such a bottleneck as exemplified by pre-Victorian economy and trade. If we treat culture like we treat genes (Dawkins eat your heart out) then why were Asian and European culture so isolated? Why was Marco Polo so revered? If these cultures were isolated even 1,000 years ago what makes you think that gene flow was unrestricted for the million years before that?

However, the "slow" expansion of a technologically advanced modern human culture that easily outcompeted human cousins would do the trick. Imagine crude H. erectus weapons that had to compete against slender spears thrown by an atlatl. It's not really fair. These human cousins would either move to other hunting grounds or try to assimilate themselves into the spreading African population.

The world as a whole is broken up into geographic regions with geographic bottlenecks between them which would limit gene flow. Also, mate selection is limited by migration and geography. During this time period how many woman in Asia had mates that were born in Africa? Were parents more likely to be from the same geographic area or from disparate parts of the globe?The MR model requires African DNA to move from Africa to Asia through many intermediaries. I don't know about you, but 95% of my DNA is not from my father. It is a 50/50 split between my father and mother. If African DNA must be passed from one population to the next it will be continually diluted by DNA from local populations with each generation as it moves away from Africa. What you seem to be arguing for is a type of genetic homeopathy where serial dilution in water does not dilute the drug of interest.

The problem is that 95% of modern human DNA across the globe is of African origin with about a 5% contribution from Neanderthals and possibly the species found in Denisova. This data would seem to indicate that the OoA mechanism is the major mechanism with the MH mechanism making a small contribution. It isn't black and white, but it is certainly tilted heavily towards one side of the grey scale.What Jon seems to be arguing is that the MH model predicts that 95% of human DNA worldwide would be African in origin due to the large population in Africa (Jon: please correct me if I got this wrong). I don't see how this can work due to restricted gene flow between human populations caused by geographic bottlenecks.

I think this is best viewed in terms of mechanism. We have two different mechanism for dispersing human DNA. One is gene flow while the other is migration. Both mechanisms can operate at the same time. You can have Paleo-Africans migrating across the globe that do in fact outcompete human species that were already there. These african populations would, according to the OoA mechanism, only breed within their group. However, we all know that humans aren't all that picky. Some outbreeding did occur per the MH mechanism, but it was relatively little compared to the OoA mechanism (at least according to my judgement thus far). Correct. It is 95% OoA and 5% MH, or thereabouts. It is a mixture of the two mechanisms with OoA being the predominant mechanism.

There was some regional DNA (again, about 5%) that made it into the African population that migrated out of Africa. I'm not quite sure what you are asking.The other point worth mentioning is that the Denisova DNA was distinct from African DNA, as distinct as neanderthal and african DNA. What we see in Papau New Guniea is 95% African DNA with a splash of Denisova DNA. If MH were the predominate mechanism you would expect a much stronger input from the Denisova DNA. Yes, there was some interbreeding between the populations, but it appears that it was limited.

A comparison of African, Neanderthal, and Denisovan DNA demonstrates that there was a discontinuity.

Is there anything that would be inconsistent with MH?ABE:The MH model that you quoted states that there was a continuous human population from the present back to a million years before present. Are you now arguing that this same model also predicts a discontinuous population for hundreds of thousands of years within that time frame?Edited by Taq, : No reason given.

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.

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

Jon,In a previous post you asked, "Are presently isolated peoples not human?".What I asked in return is if these presently isolated peoples have genetically diverged from other modern human to the extent seen in a comparison of Paleo-African, Neanderthal, and Denisovian populations.What I am getting at is that there had to be a genetic barrier between the paleo groups (be it geogrpahic or otherwise) in order to create the amount of divergence seen in these contemporaneous human populations. The isolation had to last longer than that seen for modern isolated human populations (which for Australian populations is 50,000 as a max) as demonstrated by the lower divergence of modern human populations compared to the higher divergence seen in paleo groups. This seems to argue strongly against a genetically continuous paleo-human population.Edited by Taq, : No reason given.Edited by Taq, : No reason given.

This was not so for Paleo-humans. The genetic data demonstrates that anatomically modern humans (Africans), Neanderthals, and Denisovians shared a common ancestor that existed ca. 350,000 years ago for the vast majority of the genomes. They were not a genetically continuous population. Yes, there are bits here and there which evidence limited outbreeding, but by and large the populations were separate for whatever reason. How does African DNA swamp out Siberian DNA through gene flow alone across those geographic distances? You would need intermediate populations, wouldn't you? African DNA would be diluted in each intermediate population which could not lead to the 95% African DNA found in ALL modern human populations EVERYWHERE.

You also need gene flow between the non-migrating populations. This is falsified by the divergence seen in these paleo populations. It would seem to require some continuity for the last 350,000 years which, according to the evidence, did not happen between Africans, Neanderthals, and this Denisova species.

It would have to be humongous, as sfs has pointed out. It would have to be on the same scale as . . . well, as if the Africans migrated and settled in the area. The dilution is unavoidable as I have already pointed out. A paleo-human on the coast of the Pacific Ocean is much more likely to mate with someone also from the same coastal region as they are an African. This is true all the way to the intersection of Africa and the Arabian peninsula.