How would you respond to Steve Sailer's arguments about the existence (and relevance) of race (seen, for instance, here: http://www.vdare.com/sailer/presentation.htm).
Good question. Such a good question, I am repeating a slightly expanded version of my response as a new post.
As you would expect from Sailer, his presentation is the most intelligent presentation of the distinction I have seen. Except he makes no differentiation between race and ethnicity. Afghanistan, for example, is not a place of different races (in the modern sense) but of different ethnicities.
People form groups, but they then tend to seriously over-estimate the significance of the groups. Witness the ascription of characteristics to 'left' and 'right' or 'liberal' and 'conservative' by partisans of said groupings.
In some ways, the medievals were more clever about this. For them 'race' and 'tongue' meant much the same -- a person of my race was a person who spoke my language. Thus, I could communicate far more easily with, was likely to share a larger set of references, expectations, even preferences with them. (Afghanistan would be a place of different races to the medievals: but they had little experience with the continent-wide groupings we moderns call 'race'.) If one presumes differing capacity to communicate (i.e. takes a transaction cost analysis) one can explain most of the apparently "racial" patterns in modern societies, particularly in things like hiring and housing.
Skin colour and other physical features make easy "markers". But, as Sailer implies, not exactly precise ones. (Jew-haters have had terrible difficulty with that.) And ones which people have put widely different importance to over time. (The medievals put almost none at all, for example. They wanted to know your religion and your language: sensible folk, since they are likely to have real effects on behaviour.) The historical contingency of racial signification is something many of the "race does not exist" crowd are very aware of.
There are certainly genetic clumpings which have, for example, medical significance. (And sporting significance: folk of sub-Saharan African background rarely make champion swimmers because of natural buoyancy issues.) But race mainly matters because people think it matters and because language and culture do matter for interactions while language and culture have some (often, but not always, quite strong) association with ethnicity and thus race. But language and culture are a lot more plastic over time than ethnicity which is a lot more plastic over time than race. So, even conceding the sensible bits in Sailer, race is not what one should be concerned with for moral judgment, for public policy (outside some medical applications) and so on.