In the animal world, females can go to impressive lengths to avoid sex. The explanation lies in a conflict of interest between males and females over how often to mate.
In general, males pass on more of their genes if they mate with as many different partners as possible, but that’s not the case for females, whose eggs are finite in number. This “battle of the sexes” over the frequency of mating has led to some remarkable male strategies to get sex – and female counter-strategies to avoid it.
Contrary to early beliefs, the females of many species benefit from mating with several different males. Even females in apparently monogamous partnerships may solicit covert sex with other males. Australian fairy wrens are the kings and queens of infidelity, with up to three-quarters of a female’s chicks fathered by a male who is not her social partner. In species that form pair bonds, infidelity is often rampant – and in species that don’t form pair bonds, mating with multiple partners tends to be the rule rather than the exception.
Females clearly don’t try to avoid sex altogether, but they do generally mate the minimum number of times necessary to fertilise all their eggs or to gain other benefits. For instance, many female insects mate with multiple males because the males bribe them with nutritious food or other gifts. Females may also gain genetic...
