baboons live in large harems or multimale troops.
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
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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 orangutan): Small groups of females gave him the chance to monopolize the whole group and call it his harem (for instance, the gorilla). He would have to share large groups with other males (for instance, the chimp).
That picture has been complicated by one factor: 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 prefers 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 most impressed them with their displays. They then rear their young without any help from the males.
The nearby red grouse are territorial and monogamous; the cock is almost as attentive to the chicks as the hens: The two species share the same food, habitat, and enemies, yet have entirely different mating systems. Why? My preferred explanation, and that of most biologists who have studied them, is that they have different histories. Black grouse are the descendants of forest dwellers, and it was in the forest that their maternal ancestors developed the habit of choosing males according to genetic quality rather than territory:"
HUNTERS OR GATHERERS
The lesson for humanity is obvious: To determine our mating system we need to know our natural habitat and our past: We have lived mostly in cities for less than one thousand years. We have POLYGAMY AND THE NATURE OF MEN
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been agricultural for less than ten thousand: These are mere eye blinks. For more than a million years before that we were recognizably human and living, mostly in Africa, probably as hunter-gatherers, or foragers, as anthropologists now prefer to say. So inside the skull of a modern city dweller there resides a brain designed for hunting and gathering in small groups on the African savanna.
Whatever humanity 's mating system was then is what is " natural "
for him now.
Robert Foley is an anthropologist at Cambridge University who has tried to piece together the history of our social system: He starts with the fact that all apes share the habit of females leaving their natal group, whereas all baboons share the habit of males leaving their natal group: It seems to be fairly hard for a species to switch from female exogamy to male exogamy, or vice versa. On average, human beings are typical apes in this respect even today. In most societies women travel to live with their husbands, whereas men tend to remain close to their relatives: There are many exceptions, though: In some but not most traditional human societies, men move to women.
Female exogamy means that apes are largely devoid of mechanisms for females to build coalitions of relatives. A young•
female chimpanzee generally must leave her mother 's group and join a strange group dominated by unfamiliar males: To do so, she must gain favor with the females that already live in her new tribe.
A male, by contrast, stays with his group and allies himself with powerful relatives in the hope of inheriting their status later: So much for the ape ' s legacy to mankind: What about the habitat in which he lived? Toward the end of the Miocene era, some 25 million years ago, Africa 's forests began to contract. Drier, more seasonal habitats—grasslands, scrublands, savannas—began to spread. About 7 million years ago the ancestors of mankind began to diverge from the ancestors of modern chimpanzees. Even more than 'chimps and much more than gorillas, mankind 's ancestors moved into these new dry habitats and gradually adapted to them: We know this because the earliest fossils of manlike apes (the australopithecines) were living in places that at the time were not cov-
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ered by forest—at Hadar in Ethiopia and Olduvai in Tanzania. Presumably, these relatively open habitats favored larger groups as they did for chimps and baboons, the two other open-country primates.
As socioecologists find again and again, the more open the habitat, the bigger the group, both because big groups can be more vigilant in spotting predators and because the food is usually found in a patchier pattern. For reasons that are not especially persuasive (principally the apparently great size difference of males and females), most anthropologists believe the early australopithecines lived in single-male harems, like gorillas and some species of baboon."
But then, sometime around 3 million years ago, the hominid lineage split in two (or more). Robert Foley believes the increasingly seasonal pattern of rainfall made the life-style of the original ape-man untenable, for its diet of fruit, seeds, and perhaps insects became increasingly rare in dry seasons. One line of its descendants developed especially robust jaws and teeth to deal with a diet increasingly dominated by coarse plants. Australopithecus robus-tus, or nutcracker marl, could then subsist on coarse seeds and leaves during lean seasons. Its anatomy supplies meager clues, but Foley guesses that nutcrackers lived in multimale groups, like chimps:" s
The other line, however, embarked on an entirely different path: The animals known as Homo took to a diet of meat. By I.6
million years ago, when Homo erectus was living in Africa, he was without question the most carnivorous monkey or ape the world had ever known. That much is clear from the bones he left at his campsites. He may have scavenged them from lion kills or perhaps begun to use tools to kill game himself. But increasingly, in lean seasons, he could rely on a supply of meat: As Foley and P. C: Lee put it, "While the causes of meat-eating are ecological, the consequences would be distributional and social. " To hunt, or even more, to seek lion kills, required a man to range farther from home and to rely on his companions for coordinated help. Whether as a result of this or coincidentally, his body embarked on a series of coordinated gradual changes. The shape of the skull began to retain more POLYGAMY AND THE NATURE OF MEN