Fluctuating asymmetry and body weight in men and women: Implications for sexual selection

Abstract

Fluctuating asymmetry (FA), small random fluctuations from perfect bilateral symmetry, is an indicator of developmental stability and therefore of good genes. Sexually selected weapons, such as the canine teeth of some primates, often show a negative relationship between FA and size of weapon. This suggests that it is only the males with the best genes who are able to produce large symmetrical weapons. Male body mass, which may improve fighting success, is not bilaterally symmetrical, and little is known of its relationship with FA. It is shown that for human males the body weight in adults is negatively related to FA; this suggests that male body weight is condition-dependent in that it is only individuals with the best genes who are able to develop and maintain large size. There is no relationship between weight and FA in children. For human females, there is a positive correlation between body weight and FA in adults but not in children; the implications of this finding for the understanding of the selection pressures that operate on women's weight are discussed.