Andrew Sullivan and Ta-Nahisi are thumping away at that old meme of "race as a social construct." Well, all our concepts are, you know. One point that is absolutely clear is that there are no magic lines which one can use to divide humans neatly into three, five, or twenty-seven clear and distinct races. At the same time, most of us can look at another of us and guess something about where most of our ancestors came from.
Populations differ on average, and differed more before the modern era started moving people around in large numbers. It's perfectly obvious that there are systematic differences, some of them easy to recognize, between populations that have lived in Europe or the Congo for six hundred years. Some of those differences will persist in those with some ancestry from one place or another that that have lived in another place for a couple of hundred years.
The fact that race is a social construct, with no absolute biological undepinning does not say anything about the fact that, for example, Americans with more African ancestry might or might not have more musical talent, or running speed, or various other attributes. Of course the ugly cousin in the corner is the nasty issue of IQ. I'm pretty sure that we don't know enough right now to say whether the differences in IQ noticed between populations are of social, genetic, or other origin. Eventually we will know something about the biology of IQ.
In the meantime, attempts at social engineering, say via. immigration policies that discriminate by race, are as pointless as they are invidious.