Alberto said:
So how can a DNA test prove that they are not [a part of] our ancestors?
I'm sorry for being sloppy, but when I said "there are no traces of Neanderthal genes left in modern populations" I was trying so hard not to say "Neanderthals were not the ancestors of any modern people" that I failed to be sufficiently precise in what I was saying.
Of course, we have genes in common with Neanderthals, chimpanzees, and for that matter dogs, fish, lampreys, starfish, insects and squid. However, there are also genes that vary from species to species, and also others that vary for individuals within a species. This last class of genes are the kind that population geneticists deal with. It's quite common for population geneticists to say things like "Alice shares half of her father's genes", whereas strictly speaking she shares almost all of his genes as most genes don't vary from person to person. And in this case, I was talking about this variability as well.
The study of both mitochondrial and nuclear genes from Neanderthals show that for those genes that vary between individuals (rather than the ones that all humans and Neanderthals have in common) the Neanderthal genes are far outside the normal range of human variability. Indeed, they're something like four times as far out from the average human sequences as the human distribution is wide. Comparisons of hypervariable gene sequences between Neanderthals, modern Europeans and native human populations from other continents show that Neanderthals are no closer to modern Europeans than to other human populations.
The current estimate is that humans and chimpanzees diverged 4-5 million years ago, humans and Neanderthals about 0.5 million years ago, and modern humans about 0.1 million years ago.
However, it's at least logically possible - or so it seems to me; Charlie or someone else more knowledgeable might correct me - that some modern humans are descended from Neanderthals but that the characteristically Neanderthal genes have been diluted to the vanishing point. There are certainly skeletons that are claimed to show both modern human and Neanderthal characteristics, so some interbreeding may have been going on.
Rich _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
