DNA Tests can predict a trait that would cause you to self-identify, but that doesn't relate to the rest of your gene profile...and that trait (like hair consistency, nose size and shape etc) may have nothing to do with the other result you're trying to measure. I may self-identify as black because I full lips, but if you then try to measure my athleticism, you may find that's dictated by genes I received from someone Native American or white in my ancestry.
Alleles tend to correlate with each other.
For instance, it is possible for conventionally black people to have blonde hair and/or blue eyes, since the alleles that control hair and eye color are, to some extent, different than those that control skin color. Some black people do indeed have blonde hair and/or blue eyes, but most of them don't.
If I ask you to estimate the probability that a person randomly sampled from the world population has blue eyes, you can do no better than aswer with the worldwide prevalence of blue eyes.
If I then tell you that this person is black, then you can improve the a posteriori probability of your prediction by updating it to the, much lower, prevalence of blue eyes among self-reported black people.
We can do the same even for traits that are not immediately visible, yet entirely genetic, such as lactose tolerance or blood type.
This is evidence that self-reported race is an epistemically useful concept.
EDIT:
They recently tested Snoop Dogg and Charles Barkley for a bit on the George Lopez Show. Snoop Dogg has far more stereotypically "black" physical traits," particularly much darker skin...which would lead you to identify as being more black and having more African Ancestry. It turns out Snoop Dogg was only 70% black, and Charles Barkley's percentage was higher. If you think Snoop Dogg's data, is more indicative of "black genes" and what they result in, you'd be wrong. Thus, self-reporting is not objective scientific data about DNA categories.
Actually, they are both self-reported black people and the DNA test detected primarily sub-Saharan African ancestry in both of them.
...If I ask you to estimate the probability that a person randomly sampled from the world population has blue eyes, you can do no better than aswer with the worldwide prevalence of blue eyes. If I then tell you that this person is black, then you can improve the a posteriori probability of your prediction by updating it to the, much lower, prevalence of blue eyes among self-reported black people. We can do the same even for traits that are not immediately visible, yet entirely genetic, such as lactose tolerance or blood type.
This is evidence that self-report
Idang Alibi of Abuja, Nigeria writes on the James Watson affair:
An intriguing opening. Is Idang Alibi about to take a position on the real heart of the uproar?
Darn, it's just a lecture on personal and national responsibility. Of course, for African nationals, taking responsibility for their country's problems is the most productive attitude regardless. But it doesn't engage with the controversies that got Watson fired.
Later in the article came this:
This intrigued me for two reasons: First, I'm always on the lookout for yet another case of theology making a falsifiable experimental prediction. And second, the prediction follows obviously if God is just, but what does skin colour have to do with it at all?
A great deal has already been said about the Watson affair, and I suspect that in most respects I have little to contribute that has not been said before.
But why is it that the rest of the world seems to think that individual genetic differences are okay, whereas racial genetic differences in intelligence are not? Am I the only one who's every bit as horrified by the proposition that there's any way whatsoever to be screwed before you even start, whether it's genes or lead-based paint or Down's Syndrome? What difference does skin colour make? At all?
This is only half a rhetorical question. Race adds extra controversy to anything; in that sense, it's obvious what difference skin colour makes politically. However, just because this attitude is common, should not cause us to overlook its insanity. Some kind of different psychological processing is taking place around individually-unfair intelligence distributions, and group-unfair intelligence distributions.
So, in defiance of this psychological difference, and in defiance of politics, let me point out that a group injustice has no existence apart from injustice to individuals. It's individuals who have brains to experience suffering. It's individuals who deserve, and often don't get, a fair chance at life. If God has not given intelligence in equal measure to all his children, God stands convicted of a crime against humanity, period. Skin colour has nothing to do with it, nothing at all.
And I don't think there's any serious scholar of intelligence who disputes that God has been definitively shown to be most terribly unfair. Never mind the airtight case that intelligence has a hereditary genetic component among individuals; if you think that being born with Down's Syndrome doesn't impact life outcomes, then you are on crack. What about lead-based paint? Does it not count, because parents theoretically could have prevented it but didn't? In the beginning no one knew that it was damaging. How is it just for such a tiny mistake to have such huge, irrevocable consequences? And regardless, would not a just God damn us for only our own choices? Kids don't choose to live in apartments with lead-based paint.
So much for God being "just", unless you count the people whom God has just screwed over. Maybe that's part of the fuel in the burning controversy - that people do realize, on some level, the implications for religion. They can rationalize away the implications of a child born with no legs, but not a child born with no possibility of ever understanding calculus. But then this doesn't help explain the original observation, which is that people, for some odd reason, think that adding race makes it worse somehow.
And why is my own perspective, apparently, unusual? Perhaps because I also think that intelligence deficits will be fixable given sufficiently advanced technology, biotech or nanotech. When truly huge horrors are believed unfixable, the mind's eye tends to just skip over the hideous unfairness - for much the same reason you don't deliberately rest your hand on a hot stoveburner; it hurts.