I think it goes too far the other way to point out that there is no defined COLLECTION of genetic traits that make up "race." and call that the end of the argument. I am quite sute you could not unequivocally say that sample X is a negro or whatever, but that does not mean that humans are homogeneous.

Populations have differing genetic makeup, and some are more closely related than others. Forget the idea of race. But the flow of genetic variance around the world can be tracked. We can find out that the indiginous folks from one part of the world are more closely related to those in some second place than they aer to those in a third. I know culturally my forebears came from western Europe as opposed to southern europe or africa or Kamchatka or Ceylon. Even if all of those might be "caucasians."

Rather than scream "Oh God it's the race thing again," we might look to see what this effort just might show us about ourselves.