quote:Work has also been done on ancient anatomically modern human remains from the same time period.
Do you meant he Mungo Lake results or cro magnon? Mungo Lake is really controversial and is probably an artifact. The cro magnon results have as yet, not been independently replicated so are tentative.
quote:Mammuthus's point of mitDNA being a maternal lineage and nuclear DNA being both maternal and paternal is important. However, I find it unlikely that only male neanderthals mated with human femals and human males only mated with neanderthal women when interbreeding did occur.
Actually, depending on how they co-existed, I would expect this to be the case. If they were competeing for resources, neandertal and human males would most likely produce hybrids via rape. That would mean introgression of neandertal and human Y chromsomes into each others populations but maintenance of separate mtDNA gene pools.
Another problem is given the relatively low amoung of genetic diversity of humans relative to other great apes, we may simply have lost a lot of genetic diversity by chance and thus the haplotypes are simply not detected when screeing mondern humans but are a part of our genetic history. This was actually the conclusion drawn from the Mungo Lake study where they found a really different mtDNA haplotype in an anatomically modern human fossil from Australia that was very old.
Here are links to references for the two cases I brought up.
Caramelli D, Lalueza-Fox C, Vernesi C, Lari M, Casoli A, Mallegni F, Chiarelli B, Dupanloup I, Bertranpetit J, Barbujani G, Bertorelle G. Related Articles, Links Evidence for a genetic discontinuity between Neandertals and 24,000-year-old anatomically modern Europeans. Proc Natl Acad Sci U S A. 2003 May 27;100(11):6593-7. Epub 2003 May 12.
Mungo Lake Adcock GJ, Dennis ES, Easteal S, Huttley GA, Jermiin LS, Peacock WJ, Thorne A. Related Articles, Links Mitochondrial DNA sequences in ancient Australians: Implications for modern human origins. Proc Natl Acad Sci U S A. 2001 Jan 16;98(2):537-42.Erratum in: Proc Natl Acad Sci U S A 2002 Jan 8;99(1):541.
quote:Very good point. I tend to project current "mating strategies" on ancient cultures. However, if this were common you wouldn't expect large diffences in morphology. Afterall, neanderthals were put into a different group not because of their DNA but because of their morphology. I have always accepted that occasional interbreeding could happen and be undetectable in the fossil record and in DNA studies. However, consistent interbreeding would probably show up in both.
I can think of a pretty nice example of two very similar AND interfertile species that remain both genetically and morphologically distinct. Loxodonta africana and Loxodonta cyclotis the savannah and forest African elephant respectively. They have clear morphological distinctions and their ranges overlap. Studies of microsatellites show that they do on occassion form hybrids but that even though their ranges overlap, introgression is minimal see Roca AL, Georgiadis N, Pecon-Slattery J, O'Brien SJ. Related Articles, Links Genetic evidence for two species of elephant in Africa. Science. 2001 Aug 24;293(5534):1473-7.
Sexual selection or niche selection may prevent large scale introgression as each of the two species is specialized for a distinct habitat and the F1 hybrids (and beyond) may be less fit than either parent species.
My worry about Mungo Lake is that the sequence obtained is almost identical to a Numt on chromosome 11 in all humans. They did not do a very rigorous study (at least not at the level Krings et al. 1997 did with the neandertal type specimen) and thus if it looks like a Numt it may very well be one. That would collapse their entire arguement and the conclusions would have to be thrown out.
I think the problem with that is there is (from dating of neandertal and cro magnon sites) overlap i.e. in Croatia there is a site where neandertal and cro magnon fossils are found in the same layers and have similar carbon dates. At about 28 Kya, the neandertal fossils stop appearing in the record and cro magnon continue.