The Red Queen_ Sex and the Evolution of Human Nature - Matt Ridley [114]
With concealed ovulation came continual sexual interest. Although women are more likely to initiate sex, masturbate, have an affair with a lover, or be accompanied by their husband on the day of ovulation than on other days,30 it is none the less true that human beings of both sexes are interested in sex at all times of the menstrual cycle; both men and women have intercourse whenever they feel like it, without reference to hormonal events. Compared with many animals, we are astonishingly hooked on copulation. Desmond Morris called man ‘the sexiest primate alive’31 (but that was before anybody studied bonobos). Other animals that copulate frequently – lions, bonobos, acorn woodpeckers, goshawks, white ibises – do so for reasons of sperm competition. Males of the first three species live in groups that share access to females, so every male must copulate as frequently as he can or risk another male’s sperm reaching the egg first. Goshawks and white ibises do so to swamp any sperm that might have been received by the female while the male was away at work. Since it is clear that humanity is not a promiscuous species – even the most carefully organized free-love commune soon falls apart under the pressure of jealousy and possessiveness – the case of the ibis is the most pertinent for man: a colonial, monogamous animal, driven by the threat of adultery into the habit of frequent copulation. At least the male ibis need only keep up his sex-six-times-a-day routine for a few days each season before egg laying. Men must keep up sex-twice-a-week for years.32
But concealed ovulation in women cannot have evolved for the convenience of the man. In the late 1970s there was a flurry of speculative theorizing about the evolutionary cause of concealed ovulation. Many of the ideas apply only to human beings. An example is Nancy Burley’s suggestion that ancestral women with unconcealed ovulation learnt to be celibate when fertile because of the uniquely painful and dangerous business of human childbirth; but such women left behind no descendants, so the rare exceptions who could not detect their own ovulation mothered the human race – yet concealed ovulation is a habit we share with some monkeys and at least one ape (the orang-utan). It is also a habit we share with nearly all birds. Only our absurdly parochial anthropocentrism has allowed us to think that silent ovulation is special.
None the less, it is worth going through the attempted explanations of what Robert Smith once called human ‘reproductive inscrutability’, because they shed an interesting light on the theory of sperm competition. They come in two kinds: those suggesting concealed ovulation as a way of ensuring that fathers did not desert their young, and those suggesting the exact opposite. The first kind of argument went as follows: because he does not know when his wife is fertile, a husband must stay around and have sex with her often to be sure of fathering her children. This keeps him from mischief and ensures he is still around to help rear the babies.33
The second kind of argument went thus: if females wish to be discriminating in their choice of partner, it makes little sense to advertise their ovulation. Conspicuous ovulation will have the effect of attracting several males, which will either fight over the right to fertilize her, or share her. If a female wishes (is designed) to be promiscuous in order to share paternity, as chimps do, or if she wishes to set up a competition so that the best male wins her, as buffalo and elephant seals do, then it pays to advertise the moment of ovulation. But if she wishes to choose one mate herself for whatever reason, then she should keep it secret.34