Bluematter.

If the previous post did not persuade you to stop wasting your time thinking about it, McMegan links to Jim Manzi who addresses the question. He concludes his well researched piece with this:

Do genetic differences accounts for any material portion of the difference in IQ scores by self-identified racial groups in the US? The only honest answer is that we don’t know. This, not political correctness is why the American Psychological Association’s formal consensus point of view on this question is stated without qualification: “At present, this question has no scientific answer.”

All right and proper, but that's not the right question to ask. What you really want to know is this: are 'black genes' leading to materially less intelligence than 'white genes'? And the answer is simple: IQ tests can't tell you that.

My understanding is that IQ scores say nothing about 'absolute' intelligence, they only provide a ranking. Or to use terminology more familiar to some of my readers, IQ scores only have an ordinal, not a cardinal meaning. It is very well likely that someone scoring 110 is only trivially more intelligent than someone scoring 90; what the difference between 110 and 90 actually means in terms of 'amount of intelligence' is anyone's guess.

OK, I hear you say, but don't we use quasi-cardinal interpretations for IQ scores? (e.g. isn't 'normal intelligence' supposed to lie between 90 and 109?) Quoting Manzi again:

There are statistically significant differences in IQ test performance between self-identified racial and ethnic groups in the US, and these differences have been sustained over long periods of time. The specific difference that is most widely discussed is the fact that in the US Non-Hispanic whites score, on average, about 15 points (~1 STDEV) higher than African-Americans. (Leaving aside the complication that it matters exactly how we define “long periods of time”, since, for example, there is circumstantial evidence that the black-white IQ gap may have been reduced substantially over the past several decades.)

So, 15 points is the maximum possible difference between the races. We also know with certainty that environment plays a role in determining intelligence, so the difference that can be attributed to genetics is a maximum of 10 points or so, with the actual difference (if it exists) likely to be much smaller. That's nothing: let me remind you that the average (and I think also median) person scores 100 by design, that 'average' or 'normal' intelligence is a 20 point band, and that in any case IQ is a flawed measure of 'intelligence' as used in everyday language (and a 'better than random' - but not by much - predictor of 'success' in life).

To bring the human element into this, my own results from several IQ tests are uniformly distributed across a 35 points range, and while I'm pretty good at arriving to answers to almost every IQ test type question thrown at me - questions that the average person won't answer at all - I take more time than the average person to do so (does that make me more or less intelligent?). And since the human element sells, I got more for you: here is a long list of highly successful and intelligent people who were very likely autistic, and here's the corresponding long list of people with dyslexia. What's the point? Intelligence is not a uni-dimensional variable.

And just to make sure, I should also mention the Flynn effect, quoting from this (excellent) paper (free access):

Since 1932 and probably prior to that, test scores have been increasing at a rate of 3 to 6 IQ points per decade, depending on the IQ test used. The preponderance of evidence indicates that scores are continuing to rise at a constant rate (Flynn, 2006b).

And since you apparently have to be a genius to read Bluematter., I won't even draw out the implications of the following observation on the likely (non)persistence of any currently observed differences amongst races (ala Manzi's circumstantial evidence):

There is at least one exception, however. The Scandinavian countries currently are showing little or no rise in their test scores (Flynn, 2006a). As large IQ increases were seen in Norway prior to 1968, Flynn suggests that Scandinavia might have experienced early increases that have since abated. This raises the possibility that IQ increases in other industrialized nations will also end.

So in IQ we have a metric with no cardinal interpretation, with a weak correlation to 'general intelligence' and an even weaker one to 'success in life', with the observed differences between races being pretty small and most likely diminishing even before controlling for environmental characteristics.

What's the issue again?