For the last couple of decades, there has been a popular theological concept that every living human being was 100% descended from modern humans who came Out of Africa about 50,000 years ago, so therefore there hasn't been enough time for evolution to cause any changes among people, so, therefore, Science Proves the complete genetic equality of all human racial groups.

So, what happened to the not-so-modern humans who were around back then, like the Neanderthals? Well, to Prove Racism Wrong, they had to have been utterly exterminated, the victims of a 100% genocide with no living descendants whatsoever. You see, old theories that some of the old non-African humans weren't completely obliterated were racist, because that would imply that living humans aren't all identical by descent, so they had to be utterly wrong. 

In reality, it's not actually a good idea to get too worked up over some theory you hold about the distant past. It's especially not a good idea to create political/moral/religious dogmas dependent upon some assumption you make about the far past. You never know what somebody might dig up. 

It's a better idea to keep an open mind about the present. If, say, men of West African descent keep making the Olympic 100m finals, well, that's pretty interesting. There are a variety of ways that that could have come about, and there's a variety of evidence for assessing those theories. In contrast, the conventional wisdom that anybody who notices these patterns must be evil because Science Proves that these patterns shouldn't exist is just setting yourself up for a fall.  

Not long ago, it turned out that, sure enough, non-Africans tended to be a few percent Neanderthal by descent. Then, it turned out that some people (but not others) were related to an archaic group christened Denisovans. 

A new paper that came out today finds evidence of Denisovan ancestry in various islands off the southeast coast of Asia, such as the Mamanwa negritos of the Philippines and Australian Aborigines.[Widespread Denisovan admixture (Reich et al. 2011) [PDF] ] Dienekes has some follow-up on it.

Meanwhile, a second big paper that came out today (see below) says that Australian Aborigines didn't intermarry with anybody after they got to Australia 44,000 years ago. 

You'll notice that there seem to be at least superficially contradictory lessons here about human nature: the ancestors of Australian Aborigines mated with a different quasi-species somewhere in the past, then maintained splendid isolation genetically for many tens of thousands of years in Australia, with no subsequent intruders mating with them until the 18th Century. So, maybe the general rule to draw from this is that You Can't Tell about human history. You've got to go look it up.