The Red Queen_ Sex and the Evolution of Human Nature - Matt Ridley [92]
Why Play Sexual Monopoly?
But the polygamy threshold is a bird-centric view. Those who study mammals take a rather different view, for virtually all mammals lie so far above the polygamy threshold that the four commandments are irrelevant. Male mammals can be of so little use to their mates during pregnancy that it need not concern the females whether the males have already married. Humanity is a startling exception to this rule. Because children are fed by their parents for so long, they are more like baby birds than baby mammals. The female can do a great deal better by choosing an unmarried wimp of a husband who will stay around to help rear the young than by marrying a philandering chief if she has to do all the work herself. That is a point to which I shall return in the next chapter. For the moment, forget people and think about deer.
A female deer has little need of a monopolized male. He cannot produce milk or bring grass to the young. So the mating system of a deer is determined by the battle among males, which in turn is determined by how females decide to distribute themselves. Where females live in herds (for example, red deer), males can be harem-masters. Where females live alone (for example, roe deer), males are territorial and mostly monogamous. Each species has its own pattern, depending on the behaviour of the females.
In the 1970s zoologists began to investigate these patterns to try to find out what determined a species’ mating system. They coined a new term, ‘socioecology’, in the process. Its most successful forays were into antelope and monkey society. Two studies concluded that the mating system of an antelope or a primate could be safely predicted from its ecology. Small, forest antelopes are selective feeders and as a consequence, solitary and monogamous. Middle-sized, open-woodland ones live in small groups and form harems. Big, plains antelopes, such as the eland, live in great herds and are promiscuous. At first, a very similar system seemed to apply to monkeys and apes. Small, nocturnal bushbabies are solitary and monogamous; leaf-eating indris live in harems; forest-fringe dwelling gorillas live in small harems; tree-savannah chimpanzee live in large, promiscuous groups; grassland baboons live in large harems or multi-male troops.22
It began to look as if such ecological determinism was on to something. The logic behind it was that female mammals set out to distribute themselves without regard to sex, living alone or in small groups or in large groups, according to the dictates of food and safety. Males then set out to monopolize as many females as possible either by guarding groups of females directly or by defending a territory in which females lived. Solitary, widely dispersed females gave a male only one option: to monopolize a single female’s home range and be her faithful husband (for instance, the gibbon). Females that were solitary but less far apart gave him the chance to monopolize the home ranges of two or more separate females (for instance, the orang-utan). Small groups of females gave him the chance to monopolize the whole group and call it his harem (for instance, the gorilla). Large groups he would have to share with other males (for instance, the chimpanzee).
That picture has been complicated by one factor, which is that a species’ recent history can influence what mating system it ends up with, or to put it more simply, the same ecology can produce two different mating systems, depending on the route taken to get there. On Northumbrian moors, the red grouse and the black grouse live in virtually identical habitats. The black grouse prefer bushy areas and places that are not too heavily grazed by sheep, but apart from that, they are ecological brothers. Yet the black grouse gather in spring at spectacular leks, where all the females mate with just one or two males, those that have