A Harvard Law student, Stephanie Grace, wrote a private e-mail to fellow classmates about a discussion at a dinner party. Money quote:
I absolutely do not rule out the possibility that African Americans are, on average, genetically predisposed to be less intelligent. I could also obviously be convinced that by controlling for the right variables, we would see that they are, in fact, as intelligent as white people under the same circumstances. The fact is, some things are genetic. African Americans tend to have darker skin. Irish people are more likely to have red hair. (Now on to the more controversial:) Women tend to perform less well in math due at least in part to prenatal levels of testosterone, which also account for variations in mathematics performance within genders. This suggests to me that some part of intelligence is genetic, just like identical twins raised apart tend to have very similar IQs and just like I think my babies will be geniuses and beautiful individuals whether I raise them or give them to an orphanage in Nigeria. I don’t think it is that controversial of an opinion to say I think it is at least possible that African Americans are less intelligent on a genetic level, and I didn’t mean to shy away from that opinion at dinner.
Months later one of the recipients widely forwarded the e-mail without permission from the original student, spurring outrage and apologies from the school's dean and Grace. Eugene Volokh has a good summary. He adds:
Whether there are genetic differences among racial and ethnic groups in intelligence is a question of scientific fact. Either there are, or there aren’t (or, more precisely, either there are such differences under some plausible definitions of the relevant groups and of intelligence, or there aren’t). The question is not the moral question about what we should do about those differences, if they exist. It’s not a question about what we would like the facts to be. The facts are what they are, whether we like them or not.
Given this, it seems to me that the proper approach to this question is precisely the same as the proper approach to other questions of scientific fact. One absolutely should not rule out the possibility that African Americans are, on average, genetically predisposed to be less intelligent. Likewise, to give examples involving three groups I myself belong to, one absolutely should not rule out the possibility that Jews are (say), on average, genetically predisposed to be more acquisitive, or more loyal to their narrow ethnic group than to broader groups, or that whites are genetically predisposed to be more hostile to other racial groups, or that being nonreligious is genetically linked, and that people who have those genes are genetically predisposed to be more likely to commit crime or cheat on their spouses or what have you. One should also obviously be willing to be convinced by evidence that shows that, by controlling for the right variables, we would see that those groups are, in fact, identical to other groups under the same circumstances.
One should not rule out possibilities in the absence of conclusive evidence, for the simple reason that one then has no factual basis to rule out those possibilities. And since on many things the evidence will rarely be conclusive, one shouldn’t rule out those possibilities categorically at all. And one should also be open to the evidence that exists, and to being convinced by it in one or the other direction (to the degree of conviction that is warranted by the evidence).
[T]he very attempt to suppress the openness to the possibility that there might be racial differences will make it impossible to disprove that possibility. Even if then the scientific community loudly says, “The evidence is clear: There are no racial differences in intelligence,” that statement should no longer be credible to us. Scientific consensus is trustworthy only to the extent that it’s the result of a process in which scientists — and others — are free to espouse all rival views. To the extent that espousing some views is too dangerous, the consensus that then emerges without the expression and discussion of those views stops being reliable.
So if you hope — as I do — that there are no racial differences in intelligence, and want to be able to reach that conclusion at some point with confidence based on science, not faith, you should be defending people who express an openness to the alternative scientific claim (that there are racial differences). It is only through such openness, and through allowing people to defend that claim, that the position that you hope is true can actually be demonstrated to be true.