It's just a theoretical possibility, one that will only be realized if the circumstances of evolution are conducive to its realization. Thus there was lots of opportunity for the flourishing of genes that led humans to discriminate between the two, favoring the former at the expense of the latter. But in the case of comparable discrimination between members of one's own race and members of other races, there was no significant opportunity for the evolution of such a trait. None of this is to suggest that human nature doesn't vastly complicate race relations. People are obviously inclined to derogate groups whose interests seem to clash with those of their own group, and to identify those groups by whatever means are available.
Skin color can be an unfortunately handy means of doing the identifying.
What's more, kin selection itself may complicate race relations in various subtle ways. No doubt some of my animus toward the article is related to these comments about my book. The same opinion is held by, for example, George Williams, one of the greatest evolutionary biologists of this century and arguably the chief architect of evolutionary psychology. All rights reserved.