BREAST ASYMMETRY, SEXUAL SELECTION, AND HUMAN REPRODUCTIVE SUCCESS

Breasts of human females are large compared to those of closely relate d primate species, and they can thus be hypothesized recently or curre ntly to have been subject to directional sexual selection. Here we sho w that (1) large breasts have higher levels of fluctuating asymmetry t han small breasts, (2) breast fluctuating asymmetry is higher in women without children than in women with at least one child, (3) breast fl uctuating symmetry is a reliable predictor of age-independent fecundit y, and (4) breast fluctuating symmetry appears to be associated with s exual selection. These conclusions were similar in studies from two cu ltures differing in fecundity and breastfeeding traditions (Spain; New Mexico, U.S.A.). Choosy males that prefer females with symmetrical br easts may experience a direct fitness benefit in terms of increased fe cundity and an indirect benefit in terms of attractive or fecund daugh ters.