Here are two more posts worth checking out. One is from Razib Khan, on the biological basis of race. The other is a follow-up from Andrew which engages (with much sincerity and seriousness) with the commenters here.
Ta-Nehisi has used an imagine of Walter White, the first African American head of the NAACP, to illustrate the pliability of the black identity. It certainly shows that there are no fixed definitions of race which are particularly useful. But that is a misconception of biological science, which is rife with exceptions and boundary conditions, and characterized by an instrumental perspective. The data above suggests that self-identified African Americans are characterized by some African ancestry, but over 90% are more than 50% African in ancestry. Walter White, who had five black great great great grandparents and 27 white ones, was almost certainly less than 20% African in ancestry. There are such people even today, but they are not typical, and do not disprove the reality that African Americans are predominantly of African ancestry.
I should be clear about something -- the invocation of Walter White or Mordecai Wyatt Johnson or Barack Obama isn't to say that most (or even many) black people share their particular ancestry. The point is that what you check on your census form in America is a product of social context. Social context is why someone who looks like me can be black (and proud, even!) in America and "colored" somewhere else. Social context is why our concept of race doesn't translate to, say, Brazil. This is a very present issue. Etta James didn't call herself "biracial." Perhaps if she were living today, she would.
Calling race a "social construct" does not mean that the biological ancestry -- and specifically West African ancestry -- of African Americans is mythical. It also doesn't mean that my ancestry has no actual implications. (See the map of sickle-cell density above.) And in the future, it may mean even more. Ancestry -- where my great-great-great-great grandparents are from -- is a fact. What you call people with that particular ancestry is not. It changes depending on where you are in the world, when you are there, and who has power.
In this time and in this place, I am the same as man who immigrates from Kenya. We are both "black." Even if our ancestry is different. I believe the article Razib links to bears this out:
As expected, PCA on our entire sample revealed the greatest genetic differentiation between the US Caucasians and the Africans, with the African Americans intermediate between them, reflecting their recent admixture between ancestors from Europe and Africa. Our estimate of European individual admixture (IA) in the African Americans was also roughly consistent with prior studies , with an average of 21.9%. We found considerable variation among individuals in terms of European IA, and a number of individuals with particularly high European IA values (eight individuals of 136, or 6% with values greater than 45%).Prior studies focusing on mtDNA and Y chromosomes have found a greater African and lesser European representation of mtDNA haplotypes compared with Y chromosome haplotypes in African Americans, suggesting a greater contribution of African matrilineal descent compared with patrilineal descent [6,7]. For example, Kayser and colleagues  estimated that 27.5% to 33.6% of Y chromosomes in African Americans are of European origin, compared with 9.0% to 15.4% of mtDNA haplotypes.
Here is Andrew on a similar question of race and ancestry:
"Race" as a term is very nebulous. But human subgroups with similar ancestries can have group differences in DNA -- and intelligence is highly unlikely to have no genetic basis at all (although most now believe its impact is greatly qualified by cultural and developmental differences).
We are, indeed, agreed. So that leaves us with this:
But what I really want TNC to address is the data. Yes, "race" is a social construct when we define it as "white", "black," "Asian" or, even more ludicrously, "Hispanic." But why then does the overwhelming data show IQ as varying in statistically significant amounts between these completely arbitrary racially constructed populations? Is the testing rigged? If the categories are arbitrary, then the IQs should be randomly distributed. But they aren't, even controlling for education, income, etc.
I do not know. Andrew is more inclined to believe that there is some group-wide genetic explanation for the IQ difference. I am more inclined to believe that the difference lies in how those groups have been treated. One thing that I am not convinced by is controlling for income and education.
African-Americans are not merely another maltreated minority on the scale of non-WASPs. They are a community whose advancement was specifically and actively retarded by American policy and private action. The antebellum South passed laws against teaching black people to read. In the postbellum South, black communities were the targets of a long-running campaign of terror. The terrorists took very specific aim at the institutions of African-American advancement. They targeted churches. They targeted businesses. And they targeted schools. In the mid-20th century, as we have been documenting, it was the policy of this country to deny African-Americans access to the same methods of wealth-building, that it was making available to whites.
This alone would be bad enough, but what makes it much worse is segregation. In his book American Apartheid, Douglass Massey looks at the dissimilarity indexes among African-Americans in various cities across the country in the mid to late 20th century. To summarize (and I can talk more about this) the lowest levels of dissimilarity in black communities are higher than the highest levels of dissimilarity among "white" immigrants.
This is not merely a problem for your local diversity and sensitivity workshop. It is a problem of wealth and power. When you create a situation in which a community has a disproportionate number of poor people, and then you hyper-segregate that community, you multiply the problems of poverty for the entire community--poor or not. That is to say that black individuals are not simply poorer and less wealthier than white individuals. Because of segregation, black individuals and white individuals of the same income and same wealth, do not live in communities of equal wealth.
The consequences of this are profound.* In this paper sociologist John Logan looked at the intersection of housing and segregation and found that, because of segregation, affluent African-American families, on average, lived in poorer neighborhoods than white families of much lower income:
For example, consider only affluent households whose incomes were above $75,000 in each year (adjusted for inflation). Table 2 shows that the average affluent white household lived in a neighborhood where the poverty share was under 10 percent in every year. But poor white households (incomes below $40,000) lived in neighborhoods with only slightly greater poverty shares, about 12 percent or 13 percent.In contrast, affluent blacks lived in neighborhoods that were 14-15 percent poor, and affluent Hispanics in neighborhoods that were about 13 percent poor. On average around the country, in this whole period of nearly two decades, affluent blacks and Hispanics lived in neighborhoods with fewer resources than did poor whites.
In a segregated America making individual one-to-one comparisons between black and white people is going to be fraught. That is the point of segregation.
What bearing does segregation have on IQ differential? I don't know. My skepticism of genetics is rooted in the fact that arguments for genetic inferiority among people of African ancestry are old, and generally have not fared well. My skepticism is also rooted in the belief that power generally seeks to justify itself. The prospect of actual equality among the races is frightening. If black and white people truly are equal on a bone-deep level, then the game might really be rigged, and we might actually have to do something about it. I think there's much more evidence of that rigging, then there is evidence of cognitive deficiency .
I must add that I can not pretend to be a dispassionate, nor impartial observer. I come from a particular place. I've now been out in the world, and seen how other people in other places live. They don't strike me as more intelligent. They strike me as better armed. There's nothing scientific about that. But I think we all have core faiths. These are mine. You've been warned.
*For more on this read Nikole Hannah-Jones' stunning piece for Pro Publica--"Living Apart: How The Government Betrayed A Landmark Civil Rights Law." It was through her work that I was exposed to Logan's research.