Bulls, Musth, and Cows
The Elephantine Mating Game
The breeding system of a species has important ecological and evolutionary consequences. Among the mammals, differences between the sexes in body size and the intensity of secondary sexual characters such as coat color or ornamentation (antlers, for instance) in males are significantly correlated with reproductive strategies. Charles Darwin (1871, Vol. II) noted that, among monogamous seals, the sexes were approximately equal in body size, while in polygynous seals, the males were up to six times larger than the females. The males of polygynous species are also more likely to sport elaborate ornamentation, such as large antlers or horns, which in Darwin's words are “singularly ill-fitted for fighting” (p. 251) but are “used chiefly or exclusively for pushing and fencing” (p. 253).
The elephant is a polygynous mammal, as are 95% of all mammals. Polygyny has been defined by William Shields as a situation when “more females than males breed, with the result that variance in reproductive success is greater in males than in females. The greater the difference in variance, the greater the degree of polygyny. ” The degree of dimorphism between the sexes is a good indicator of the degree of polygyny in a species. The elephant is one of the most sexually dimorphic of mammals. In African elephants, a full-grown male weighs twice as much as a full-grown female, making these among the most sexually dimorphic (and also polygynous) of all mammals.