Tooby and Cosmides (1992) thus suggested that most
of the genetic variation between human individuals is neutral
or functionally superficial. They did, however, concede
a possible role for “some thin films” of functionally relevant
heritable interindividual differences (Tooby & Cosmides,
1992, p. 80). The possible sources of these thin
films—frequency-dependent selection and selective responses
to local ecological conditions—are discussed in
greater detail below. What is relevant for the present purposes
is the low priority given to understanding these thin
films relative to the task of describing and explaining the
universal psychological mechanisms that humans undoubtedly
all share.