Work has also been done on ancient anatomically modern human remains from the same time period. The mitDNA sequences of those samples was different that the neander sequences dating 3,000 years older but closely matched living human sequences. Also, there are no regional differences in neander to living human sequences. This is important since neanders have only been found in Europe and not in asia or africa. Therefore, if there was interbreeding we would expect a closer match to living europeans than to asians or africans. This is not the case, and therefore supports the case for limited or non existant interbreeding between anatomically modern humans and neanderthals.
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. However, the possibility does exist. Post natal development in humans and neanderthals seems to argue against interbreeding as well, which would be independent of mitDNA lineages. So far, fossil remains of neanderthal children seems to indicate a different maturation process than that seen in human populatins. If interbreeding were occuring we would expect a melding of the two maturation processes, but we find the opposite.
The only conclusion that I have been able to draw from the data is that interbreeding was not a common occurence. The possibility of occasional interbreeding still remains. Modern human lineages may only represent those lineages that survived form the period and may not reflect interbreeding lineages present at the time of neanderthal and human cohabitation of Europe. Also, the data, to this point, does support the theory that humans and neanderthals were two different species in that genetic flow between the populations was either severely limited or non-existant. Therefore, it is possible that both neanderthals and humans are both daughter species of Homo heidelbergensis.
quote: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.
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.
quote: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.
The verification of the Mungo Lake samples would go a long way towards testing this. Also, additional cro magnon samples would also help in clearing this up. Given that the geographic ranges of neanderthals and cro magnon overlap, we need an explanation as to how the mitochondrial genomes of each species were kept separate. My hypothesis is that it was due to sexual selection and not cross-species infertility. Is this the way you see it as well, more testing and sexual selection as a possible mechanism?
quote: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.
Agreed. It would seem that the evidence is still tentative and needs further validation from other labs, as well as experiments to rule out numts.
quote:Remember, while we often say that ranges overlap, population density was also considerably smaller than today and physical barriers to travel were of a greater magnitude. If you have ever hunted, you will understand that even when you are in an area where it is known that your target species is available, it is often the case that you will never see a single critter. Even in our modern manicured wilderness, it's not unusual to find tracks crossing your path of a critter you never saw.
There is a culture of hunting here in Idaho. Almost every year someone is shot by another hunter hiding in the bush, or a horse is hit etc. Imagine missing a deer or an accidental misfire hitting another hunter trying to hide himself just like you. The odds seem slim yet it happens. I would expect the same thing to happen in Europe, where neadnerthals and cro magnon man are hunting the same herd and run into each other. This would most likely be male to male contact, but fights over hunting grounds would probably involve the invasion of living areas that would include women. This is all speculation, but I would expect that gene flow was socially restricted, not geographically restrited.
This message has been edited by Loudmouth, 10-11-2004 01:53 PM