The inter-male struggle for access to females has been documented in many species. An extreme case is the North American grouse, in which only about one in ten of the males ever gets to mate. Studies of free-ranging Rhesus monkeys show that the top 20 per cent of males in the dominance hierarchy account for about 80 per cent of the copulations and at least half hardly ever achieve copulation, apparently because of social inhibition.

A very similar degree of unevenness in male copulatory success is observed in polygamous tribes such as the Yanamamo in the Amazon (Freedman, 1979). Western society, although superficially monogamous, may well have a comparable infrastructure with a certain proportion of men ‘dropping out’ altogether from reproductive competition (‘wimps,’ deviants, schizophrenics, alcoholics and tramps), while successful businessmen, politicians, actors, television preachers and so on enjoy the favours of several wives, mistresses, groupies, etc.

By contrast, the females of most species including humans (at least in the absence of contraception) achieve their optimal breeding capacity. As Symons (1979) points out, even the most unattractive woman in a village, whom no man would admit to touching, somehow manages to get pregnant every so often.

From the ‘group selection’ point of view, this could be seen as strengthening the species by increasing the extent to which the superior males – those that are physically healthy, skilful and intelligent – pass on their genes to the next generation in greater proportion. Indeed the pattern of polygyny (one high-ranking male mating with several females) may well be essential to the survival of a species. Groups that did not adopt such a policy would suffer some degree of genetic stagnation and might soon be disadvantaged in relation to those that did.

In any case, the genetic benefits to the individual male who sequesters and impregnates more than his share of females should be sufficient to ensure that male instincts promoting the pursuit of multiple mates would be selected for. Polygyny is therefore the most widespread mating system in the mammalian, primate and human world.