Out of Africa theory, true or not?

[BioWizard]

Forest,

Would you please summarize in bullets some of the most important points made in that paper?

[Forest_Dump]

Certainly, there are three main hypotheses regarding the emergence of anatomically modern Homo sapiens and the relationship to modern humans. The regional continuity model is based on the observation that Homo erectus is found throughout Africa, Europe and Asia. Furthermore, there is continuity in some areas such as east Asia to the present.

The Total Replacement model argues that anatomically modern H.S. evolved in Africa and spread from there. The oldest AM H.s. are found there and the DNA evidecne appears to give some support.

The partial replacement model, in short, offers a blend of these two ideas and that paper is a statement on this model.

Some key points:

Few would argue that there is not a great deal of complexity in the data from these times and that there is solid evidence of "mosaic" patterns. The evidence supporting the Regional Continuity Model (associated with Wolpoff but many others) cannot be lightly dismissed although it has become obvious that, since this data cannot be ignored, an alternative tactic of launching ad hominem attacks on Wolpoff, etc. should be considered valid.

As Trinkaus points out, the DNA data supporting the replacement model has also been overextended. The problems with preservation and sample sizes should be well-known by now.

Trinkaus also reports on more recent work done on both new sites and old. Of relevance here is recent re-examination of the reputably old Australian sites. The context of the remains were on a deflated dune which exagerated the apparant age. Direct dating of the bones indicates a more recent age.

In short, the spread of modern H.s. appears to have occurred after 50,000 and probably after 40,000 B.P. The complex, mosaic patterns, including possible "hybrids" and continuity in some areas, indicates that this was not a simplistic process but that there was regional diversity early on and that this diversity persisted to the present day.

Having met and chatted with Wolpoff, although I don't (perhaps didn't is better) agree with him. He can also be a touch over-bearing. However, he is an impressive scholar who has been subjected to a lot of very unscholarly attacks and deliberate mis-understanding. Part of the problem is that too many people seem to reify fossil species as being akin to modern biological species and assign values on this basis. While given the polemic nature of competitions for research funds, etc., it is not surprising that some of his peers have joined in these attacks. However, as is also all too common, most of the worst such attacks are clearly coming from people who have not gone beyond dilletantism. Frankly, I am very tired of people taking shots at people like Wolpoff without offering anything of substance.

The DNA evidence is interesting but I will quote Trinkaus:

"These aDNA analyses have demonstrated only that some Neanderthals had mtDNA sequences outside the documented range for living humanity..."

"The aDNA is compatible with both replacement and assimilation scenarios... and we are not likely to ever have sufficient reliable neanderthal or early modern human aDNA to distinguish between replacement and a more-than-trivial level of admisture..."

[BioWizard]

Thanks FD.

So let me get this straight. Trinkaus is saying that because we can only obtain present day mitochondrial DNA, we can construct genealogy for anatomically modern humans, but we cannot use that data to discern whether AMH replaced descendents of H erectus in Asia and Africa or whether they blended with them or their descendents?

"The aDNA is compatible with both replacement and assimilation scenarios... and we are not likely to ever have sufficient reliable neanderthal or early modern human aDNA to distinguish between replacement and a more-than-trivial level of admisture..."

I thought analysis done using mitochondrial DNA obtained from three neaderthals suggested a split between them and AMH 500kya before our first appearance in East Africa. How is that not sufficient to support one model and not the other?

[Dipset-Boom]

Do you really want to know the difference between Homo Sapiens Sapiens (yes, this includes Australoids) and Homo Erectus, our brains are at least twice as big and organized much differently, our brain is extremely distinct in its two sides as well. Human variation must also be remembered, Brittney Spears dosen't look like an Australian native, but there are caucasoids and mongoloids that have just as archaic looking features, its not like its impossible for there to be a large browed, wide nosed European. I'm sure you can also find many blond white people who also do not look anything like Jessica Simpson, other than maybe the colour of his skin. It's obvious you have only studied pictures of these skulls, until you can compare the actual skulls to each other you would see a clear difference in the size of the brain cavity.

[Forest_Dump]

Ooops, only just noticed the replies to my last post here. Sorry about that Bio.

IMHO, the DNA data does appear to support one of the replacement models, at least in that area. Since I tend to lean more towards the partial replacement model myself, I should have no problem with that. The explanation could be that Neanderthals just did not get let back into the mainstream of the gene pool (hmmm, conflicting metaphors there?) However, given the available samples of DNA from that population, I prefer to remain as cautious about that as about things like the Flores fossils.

I am also cautious about the Total replacement model, however, because there does appear to be some evidence for continuity in some places. The possible hybrid specimens noted are tricky but the evidence of continuity in East Asia is stronger (e.g. the Sinodont pattern from Homo erectus to present day).

For the most part, this debate has little impact on me since I do New World archaeology. However, if either of the replacement models (partial or total) wins the debate, this would have a large impact on the timing of the first peopling of North America. Simply, to allow for a relatively early peopling of North America, we need donar populations in northeast Asia early enough to be able to negotiate some of the barriors imposed by glacial advances. If all modern populations are partially or completely descended from groups that left Africa this side of 50,000 years, for example, then taking into account things like the glacial maximum in extreme northeastern Asia, it is very tough to get people into continental North America much before 20,000 years ago. Some of the claims for dates as old as 50,000 (or older) for people in North America would be almost impossible unless the remains were from an archaic Homo sapiens not related to modern populations.