The Red Queen_ Sex and the Evolution of Human Nature - Matt Ridley [112]
What about the men? Baker and Bellis did an experiment on rats and discovered that a male rat ejaculates twice as much sperm when he knows that the female he is mating with has been near another male recently. The intrepid scientists promptly set out to test whether human beings do the same. Sure enough, they do. Men whose wives have been with them all day ejaculate much smaller amounts than men whose wives have been absent all day. It is as if the males are subconsciously compensating for any opportunities for female infidelity that might be present. But, in this particular battle of the sexes, the women have the upper hand because even if a man – again unconsciously – begins to associate his wife’s lack of late orgasms with a desire not to conceive his child, she can always respond by faking them.25
Cuckoldry Paranoia
The cuckold, however, does not stand by and accept his evolutionary lot even unto the extinction of his genes. Birkhead and Møller think that much of the behaviour of male birds can be explained on the assumption that they are in constant terror of their wives’ infidelity. Their first strategy is to guard the wife during the period when she is fertile (a day or so before each egg is laid). This many male birds do. They follow them everywhere, so that a female bird who is building a nest is often accompanied on every trip by a male who never lends a hand; he just watches. The moment she has finished laying the clutch of eggs, he relaxes his vigil and begins himself to seek adulterous opportunities.
If a male swallow cannot find his mate he often gives a loud alarm call, which causes all the swallows to fly up into the air, and effectively interrupts any adulterous act that is in progress. If the pair has just been reunited after a separation or if a strange male intrudes into the territory and is chased out, the husband will often copulate with the wife immediately afterwards, as if to ensure that his sperm are there to compete with the intruder’s.
Generally, it works. Species that practise effective mate guarding keep the adultery rate low. But some species cannot guard their mates. In herons and birds of prey, for example, husband and wife spend much of the day apart, one guarding the nest while the other collects food. These species are characterized by extremely frequent copulation. Goshawks may have sex several hundred times for every clutch of eggs. This does not prevent adultery, but it at least dilutes it.26
Just like herons and swallows, people live in monogamous pairs within large colonies. Fathers help to rear the young, if only by bringing food or money. And, crucially, because of the sexual division of labour that characterized early human hunter-gatherer societies (broadly speaking, men hunt, women gather), the sexes spend much time apart. So women have ample opportunities for adultery and men have ample incentives to guard their mates or, failing that, to copulate frequently with them.
To demonstrate that adultery is a chronic problem throughout human society, rather than an aberration of tower blocks in Britain, is paradoxically difficult: first, because the answer is so stunningly obvious that nobody has studied it; second, because it is so universally kept secret that it is almost impossible to study. It is easier to watch birds.
None the less, attempts have been made. The five hundred and seventy or so Aché people of Paraguay were hunter-gatherers until 1971, living in twelve bands, and then they gradually came into contact with the outside world and were lured into government reservations run by missionaries. Today, they no longer depend on hunted meat and gathered fruit, but grow most of their own food in gardens. But when they still depended on men’s hunting skills for much of their food, Kim Hill found an intriguing pattern. Aché men would donate any spare meat they had to women they wanted to have sex with. They