Before proceeding, we should be clear about what we are not saying. First, we are not denying that research into the genetics of human differences has been misused for appalling purposes at various points over the last two centuries. Second, we are not denying that some of the scientists who have undertaken such research were motivated by racial animus or by a desire to subjugate other people. Hence we understand the temptation to assume the worst about anyone who might be willing to entertain what we have called ‘hereditarian claims.’ Nonetheless, equating hereditarian claims with racism is a fallacy, and one that we believe is likely to end up doing more harm than good.

The thesis is basically "yes, humans do in fact differ physiologically, in groups corresponding to geography, and no it is not inherently racist to assert this."