The Red Queen: Sex and the Evolution of Human Nature

by Matt Ridley

The nuclear genes of both father and mother between them arrange that the organelles of the male are slaughtered. It is an advantage (to the male nucleus, not to the male organelles) to be of the type that allows its organelles to be killed, so that a viable offspring results. So owners of docile, suicidal organelles (in the minus gender) would proliferate. Soon any deviation from a ratio of fifty-fifty killers and victims would benefit the rarer type and cause the ratio to correct itself. Two genders have been invented: killer, which provides the organelles, and victim, which does not. Laurence Hurst of Oxford uses these arguments to predict that two genders are a consequence of sex by fusion. That is, where sex consists of the fusing of two cells, as in Chlamydomonas and most animals and plants, you find two genders. Where it consists of “conjugation”—the formation of a pipe between the two cells and the transfer of a nucleus of genes down the pipe—and there is no fusion of cells, then there is no conflict and no need for killer and victim genders. Sure enough, in those species with sex by conjugation, such as ciliated protozoa and mushrooms, there are many different genders. In those species with sex by fusion, there are almost invariably two genders.