Abstract
In polygynous mammals, mature males are usually much heavier than females. Competition for females is intense, and few males reproduce. Given the importance of the male's body size for the reproduction and social life of these species, levels of sexual dimorphism were studied in 27 species of polygynous terrestrial cetartiodactyls at the 3 most significant stages of development: birth, 6 months of age, and adulthood. Overall, there were 3 different types of changes in male-to-female (M/F) mass ratios between birth and adulthood, corresponding to the 3 categories of adult dimorphism. The change in mass ratio between birth and 6 months of age was inversely correlated to the degree of dimorphism at birth. Most adult dimorphism was acquired after weaning. On the whole, postnatal maternal care seems to have no or even an inverse effect on the evolution of dimorphism, which is apparently not consistent with the assumption of greater maternal investment in male than in female offspring among polygynous mammals.