Animals That Kill Their Young

For India's langur monkeys, infanticide works

In his classic work On Aggression, Nobel Laureate Konrad Lorenz argued that man is the only species that regularly kills its own kind. This concept, which contrasted the order and restraint in the animal world with the chaotic aggressiveness of man. reflected the mood of the time: the shadow-of-the-Bomb pessimism of the '50s and early '60s. But Lorenz was wrong; since 1963, when his book was published, naturalists have identified dozens of species that kill their own, including lions, hippos, bears, wolves, hyenas, herring gulls and more than 15 types of primates other than man.

In the new perspective, animals are not benign machines that live for the group and kill only to eat. Instead, they are programmed for selfish, even murderous acts when survival and propagation are threatened. This radical shift in thinking is shown most dramatically by studies of India's sacred monkey, the hanuman langur. In 1965, a naturalist wrote that the long-tailed black and gray langurs were "relaxed" and "nonaggressive." Now, a Harvard researcher has shown that the langur society operates more like the House of Borgia, complete with kidnaping, constant sexual harassment, group battles, abandonment of some wounded young by their mothers, and the regular practice of infanticide.

In her new book. The Langurs of Abu, Harvard Anthropologist Sarah Blaffer Hrdy, 31, portrays langur life as a "soap opera" that revolves around the struggle between the sexes. As in other species, the strongest males compete for control of each troop. What makes the langurs different is that the winner tries to bite to death the young offspring of his predecessor. The mothers resist the infanticide until the struggle looks hopeless, then pragmatically present themselves to the new ruler for copulation.

Why so brutal a society? Hrdy believes that the answer lies in the theory of sociobiology, which holds that each organism is engaged in a one-against-all struggle to get as many of its genes as possible into the next generation. That explains the sexual aggressiveness of langurs--and males of other species; it usually makes evolutionary sense for males to inseminate the maximum number of females. But why infanticide? Hrdy reasons that the grisly practice evolved among the langurs to solve a problem for the new dominant male. Because of the competition of other males, his reign over a harem or troop is usually short, and his genetic drive dictates that he impregnate the females as quickly as possible. As Hrdy explains: "By eliminating infants in the troop that are unlikely to be his own, a usurping male hastens the mother's return to sexual receptivity and reduces the time that will elapse before she bears his offspring."

Hrdy, who spent 1,500 hrs. observing langur behavior around India's Mount Abu from 1971 to 1975, documented the disappearances of 39 infants around the times of new male takeovers; she estimates that only half of all langurs survive infancy. While males shift constantly among groups, females usually spend a lifetime in one troop and cooperate in warding off danger.

When a new male ascends to power, pregnant females use deceit in an attempt to save their unborn young from his later attack: they demonstrate estrus behavior to the new leader, presumably to trick him into thinking the future offspring are his. But once the new male shows that he is determined to kill the infants, the mothers abandon their young. Though they could gang up on the male or refuse to copulate with him after infanticide, Hrdy notes, it is always in their individual self-interest to break ranks and accept him. Reason: their own male offspring will eventually benefit from the infanticidal trait.

Hrdy's portrait of the langurs is a far cry from the traditional view of animals as social creatures that act to ensure group survival. But as Lorenz's work was, it is in tune with its times. In stressing chaotic individualism at the expense of the group. The Langurs of Abu reads like a jungle version of Tom Wolfe's essay on The Me Decade.

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