Many of our categories are human constructions which map upon patterns in nature which we perceive rather darkly. The joints about which nature turns are as they are, our own names and representations are a different thing altogether. This does not mean that our categories have no utility, but we should be careful of confusing empirical distributions, our own models of those distributions, and reality as it is stripped of human interpretative artifice.
I have argued extensively on this weblog that:
1) Generating a phylogeny of human populations and individuals within those populations is trivial. You don't need many markers, depending on the grain of your phylogeny (e.g., to differentiate West Africans vs. Northern Europeans you actually can use one marker!).
2) These phylogenies reflect evolutionary history, and the trait differences are not just superficial (i.e., "skin deep").
The former proposition I believe is well established. A group such as ...
