My daughter is African American, and this is something that gets noticed here in Athens County. There are relatively few African Americans here, even though there is a major university in this town whose president is also an African American who has explicitly stated his desire to increase "diversity" on campus, principally in the form of larger numbers of members of various "underrepresented" groups. In spite of some progress in this area, the percentage of students who are African American has grown, in the eleven years that I have been here, only from 4% to about 6%.
Race, as a biological category, is largely meaningless. Indeed, the concept is defined by completely arbitrary groupings of phenotypes. African Americans are, by and large, dark skinned, though there is a continuum here that appears to run all the way from quite pale to quite dark; they tend to have very curly hair, though again there are exceptions; they tend to have broad noses, though again there are exceptions. It's interesting that you always have to add the phrase "there are exceptions", otherwise our definition of the "race" wouldn't work in some of the cases where, apparently, it's supposed to. But the necessity of adding that phrase demonstrates the arbitrariness of the category. We're just making it up to suit our needs.
There is one possible ontological correlate for these categories: it is possible that some definitions of race may come close to capturing something like geographical origin. African Americans are descended from people who came, originally, from Africa; the so-called "white" Americans are descended from people who came, mostly, from Europe and other northern climes. But even this objective trait is misleading, because if you trace these lineages back far enough in evolutionary time, we all come from Africa, no matter what we look like now.
It seems to me that the category of "race" is in some sense an artifact of our desire to be able to distinguish groups of persons, that is, it is a form of tribalism. We are interested in people who are "like" us, and we want to be able to recognize, somehow, the folks who are part of our "tribe", however that concept gets worked out in various social contexts. Visually observable traits are pretty handy in this regard, and so of course to the extent that race is definable at all it is always defined in terms of observable physical traits like skin color, hair type, etc. But to see how arbitrary this is you have only to ask yourself why it is that the dark skinned person is thought to be a member of a different "race" than the light skinned person, but the person with blue eyes is not necessarily thought to be a member of a different "race" than the person with brown eyes. Or why the red haired person is not thought to be a member of a different race than the blond person. Or why the person who is right handed is not thought to be a member of a different race than the person who is left handed. None of these traits is any less real than skin color, non is more arbitrary. And yet, none of them is used in quite the way skin color is to distinguish these "races".
When I was a kid, there were only three "races". There were Negroes, Caucasians, and--I kid you not--"Mongoloids". Yep, that's what they were called. At least, that's what they were called in 1968 when I was told all of this crap in the 5th grade. I don't know how the concept is taught, or even whether it is taught at all, in the schools nowadays. My son, who will start the eighth grade in the fall, never talks about learning such things at school, and for a 13 year old he seems to be rather refreshingly free of the sorts of prejudices that often afflict children at that age. Perhaps, as evolutionary biology comes to be taught in ever more meaningful ways in the schools, children will figure out for themselves how meaningless the category is.
The concept of race is most often deployed these days for political reasons. It would be rather pointless to have a goal of "greater diversity" at a university if it should turn out to be the case that the trait that one is attempting to diversify is meaningless. We want more African Americans to enroll here not because they have different phenotypes, but because they come from backgrounds that are interesting and diverse and they will make a genuinely positive contribution to the social and intellectual climate at the university. We don't try to recruit more redheads for these reasons, however, even though they are represented in the student population at approximately the same level as African Americans. That ought to puzzle people, but it doesn't because, of course, African Americans, as a group, have had a rather unfortunate history of having been unjustly treated, and it is thought by some to be a legitimate step towards righting past wrongs to make a particular effort at recruiting qualified folks from such groups.
The outcome of such recruitment, if it is done properly, is arguably better than the outcome of refusing to make such efforts, but I don't think that it is obviously better. The case for it can be made, but it must be made, not assumed. To assume that it is obviously better is in itself a form of racism, and racism is among the greatest social evils of our time. It will be a very long time, I think, before people stop thinking in racial categories, if only because phenotypic differences are so easily observable. But the sooner people can come to believe that there is no such category, that there really is no qualitative difference at all among human persons, the better.