The Red Queen_ Sex and the Evolution of Human Nature - Matt Ridley [110]
Emma Bovary and Female Swallows
What’s in it for the birds? For the males it is obvious enough: adulterers father more young. But for the female, it is not at all clear why she is so often unfaithful. Birkhead and Møller rejected several suggestions: that she is adulterous because of a genetic by-product of the male adulterous urge, that she is ensuring some of the sperm she gets is fertile by getting it from several sources, that she is bribed by the philandering males (as seems to be the case in some human and ape societies). None of these exactly fitted the facts. Nor did it quite work to blame her infidelity on a desire for genetic variety. There seems to be little point in having more varied children than she would have anyway.
Birkhead and Møller were left with the belief that female birds benefit by being promiscuous because it enables them to have their genetic cake and eat it – to follow the Emma Bovary strategy of adultery from within marriage. A female swallow needs a husband who will help look after her young, but by the time she arrives at the breeding site she might find all the best husbands taken. Her best tactic is therefore to mate with a mediocre husband or a husband with a good nest site and have an affair with a genetically superior neighbour. This theory is supported by the facts: females always choose more dominant, older, or more ‘attractive’ (i.e., ornamented with longer tail feathers) lovers than their husbands; they do not have affairs with bachelors (i.e., presumably, those that have been rejected by other females), but with other females’ husbands; and they sometimes incite competitions between potential lovers and choose the winners. In Møller’s study male swallows with artificially lengthened tails acquired a mate ten days sooner, were eight times as likely to have a second brood and had twice as high a chance of seducing a neighbour’s wife as ordinary male swallows.21 (Intriguingly, when female mice choose to mate with males other than those they ‘live with’, they usually choose ones whose disease-resistance genes are different from their own.22)
In short, the reason adultery is so common in colonial birds is that it enables a male bird to have more young and enables a female bird to have better young.
One of the most curious results to come out of bird studies in recent years has been the discovery that ‘attractive’ males make inattentive fathers. Nancy Burley, whose zebra finches consider each other more or less attractive according to the colour of their leg bands, first noticed this,23 and Anders Møller has since found it to be true of swallows as well. When a female mates with an attractive male, he works less hard and she works harder at bringing up the young. It is as if he feels that he has done her a favour by providing superior genes and therefore expects her to repay him with harder work around the nest. This, of course, increases her incentive to find a mediocre, but hard-working husband and cuckold him by having an affair with a super-stud next door.24
In any case, the principle – marry a nice guy but have an affair with your boss, or marry a rich but ugly man and take a handsome lover – is not unknown among female human beings. It is called having your cake and eating it. Flaubert’s Emma Bovary wanted to keep both her handsome lover and her respectable husband. The effort eventually drove her to arsenic.
The work on birds has been conducted by people who knew little of human anthropology. In just the same way, a pair of British zoologists had been studying human beings in the late 1980s, largely in isolation from the bird work. Robin Baker and Mark Bellis of Manchester University were curious to know if sperm competition happened inside women, and, if it did, whether women had any control over it. Their results have led to a bizarre and astonishing explanation of the female orgasm.
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