Why, in the great majority of animals, are there equal numbers of males and females? For John Arbuthnot, writing in 1710, it was evidence of the beneficence of God: 'for by this means it is provided, that the species may never fail, nor perish, since every male may have its female, and of a proportionable age.' But while that might do for man, it will hardly do for those many species in which there is no monogamous pair bond and no parental care, and in which one male can fertilise many females, and yet which have an equal sex ratio.

LRB 3 February 1983 | PDF Download