Tracing the Evolutionary Origins of this Sex Difference

Within ancestral human societies, i.e., bands of closely related families, the male-female difference should have accounted for most of the observable skin color variability. What role, if any, might it have played in relations between the sexes?

Symons (1995) argues that men once used skin color to assess potential mates, specifically as an index of fecundity. In the environment of evolutionary adaptedness (EEA), darker women would have been prepubescent, pregnant (90% of pregnancies cause a mild, generalized darkening), or menstruating (skin reddens around the time of menstruation). Symons adds that successive pregnancies progressively darken the skin, so that the fairest women should have been the most nubile and fecund.

One problem with this model is that light skin also characterizes young infants of either sex (although children might somehow be exempt from the search image). Another problem is that whiteness, though often associated with female beauty, does not seem to signify erotic desire in cross-cultural analyses of word meanings. Normally it signifies 'peace', 'innocence', 'purity', 'delicateness', and 'modesty' (Gergen 1967). The popularity of female suntanning since the 1920s further suggests that eroticism can be dissociated from light skin as a component of female sexual identity.

Guthrie (1970) suggests that a fairer skin is one of several infant-like features—smaller nose and chin, smoother skin texture, relative lack of body hair, higher pitch of voice—that women have evolved to deter male aggression: "the sexual differences in skin color resulted from female whiteness being selected for because it is opposite the threat coloration, although the selection pressures may have been rather mild. Light skin seems to be more paedomorphic, since individuals of all races tend to darken with age. Even in the gorilla, the most heavily pigmented of the hominoids, the young are born with very little pigment."

In some primate species, the adult female retains the infant's body color, apparently in response to a family environment that includes not only offspring but also a continually present male partner. Of the eight primate species where adult males and females differ in color, seven have the female retaining the infant's lighter color and five (63%) are monogamous—versus only 18% of all primate species (Hrdy & Hartung 1979). In monogamous animals, the male contributes more to infant care and cohabits more with the female, thus increasing her vulnerability to aggression and desertion. To reduce this risk, the female may look more like an infant as a way to inhibit aggressive impulses in her mate and to stimulate parental feelings of care. It is perhaps for similar reasons that much of mammalian sexuality seems to come from infant behaviors, like cuddling, murmuring, nipple sucking, and mouth licking.

Although our species is not fully monogamous, there does seem to have been a trend away from polygyny in hominid evolution and this trend may have favored women who retained an infantile complexion. In primates, infantile mimicry usually involves fur color, probably because fur covers most of the body surface. The primatologist Alley (1980) does, however, list "pink flesh" and "pink skin" as infant traits that elicit parental care. In a furless species like our own, skin color might have assumed even more importance. 

References

Alley, T.R. (1980). "Infantile colouration as an elicitor of caretaking behaviour in Old World primates." Primates 21:416-429.

Frost, P. (1988). "Human skin color: a possible relationship between its sexual dimorphism and its social perception." Perspectives in Biology and Medicine 32: 38-58.

Gergen, K.J. (1967). "The significance of skin color in human relations." Daedalus 96:390-406.

Guthrie, R.D. (1970). "Evolution of human threat display organs." Evolutionary Biology 4:257-302.

Hrdy, S., and J. Hartung (1979). "The evolution of sexual dichromatism among primates." American Journal of Physical Anthropology 50:450.

Symons, D. (1995). "Beauty is in the adaptations of the beholder: The evolutionary psychology of human female sexual attractiveness." In P.R. Abramson and S.D. Pinkerton (Eds.), Sexual Nature. Sexual Culture. (pp. 80-118). Chicago: University of Chicago Press.

Treves, A. (1997). "Primate natal coats: A preliminary analysis of distribution and function." American Journal of Physical Anthropology 104:47-70.

Roman painting of Arcadia and Hercules, 1st century