Researchers have observed various male animals-including insects, birds, and mammals-chasing, threatening, and attacking females. The males of many of these species are most aggressive toward potential mates, which suggests that they sometimes use violence to gain sexual access.
Jane Goodall provides us with a compelling example of how males use violence to get sex. In one of several scenarios, males gather around attractive estrous females and try to lure them away from other males for a one-on-one sexual expedition that may last for days or weeks. But females find some suitors more appealing than others and often resist the advances of less desirable males. Males often rely on aggression to counter female resistance. Goodall thinks that a male uses such aggression to train a female to fear him so that she will be more likely to surrender to his subsequent sexual advances.
Similarly, male hamadryas baboons, who form small harems by kidnapping child brides, maintain a tight rein over their females through threats and intimidation. If, when another male is nearby, a hamadryas female strays even a few feet from her mate, he shoots her a threatening stare and raises his brows. She usually responds by rushing to his side; if not, he bites the back of her neck. By repeating this behavior hundreds of times, the male lays claim to particular females months or even years before mating with them. When a female comes into estrus, she solicits sex only from her harem master, and other males rarely challenge his sexual rights to her.
These chimpanzee and hamadryas males are practicing sexual coercion: male use of force to increase the chances that a female victim will mate with him, or to decrease the chances that she will mate with someone else. But sexual coercion is much more common in some primate species than in others. Orangutans and chimpanzees are the only nonhuman primates whose males in the wild force females to copulate, while males of several other species, such as vervet monkeys and bonobos, rarely if ever try to coerce females sexually.
These dramatic differences between species provide an opportunity to investigate which factors promote or inhibit sexual coercion. For example, we might expect to find more of it in species in which males are much larger than females-and we do. However, size differences between the sexes are far from the whole story. Chimpanzee and bonobo males both have only a slight size advantage, yet while male chimps frequently resort to force, male bonobos treat the fair sex with more respect. Clearly, then, although size matters, so do other factors.
In some species, females remain in their birth communities their whole lives, joining forces with related females to defend vital food resources against other females. In such "female bonded" species, females also form alliances against aggressive males. Vervet monkeys are one such species, and among these small and exceptionally feisty African monkeys, related females gang up against males. High-ranking females use their dense network of female alliances to rule the troop; although smaller than males, they slap persistent suitors away like annoying flies.
Females in other species leave their birth communities at adolescence and spend the rest of their lives cut off from their female kin. In most such species, females do not form strong bonds with other females and rarely support one another against males. Both chimpanzees and hamadryas baboons exhibit this pattern, and, as we saw earlier, in both species females submit to sexual control by males.
This contrast between female-bonded species, in which related females gang together to thwart males, and non-female-bonded species, in which they don't, breaks down when we come to the bonobo. Female bonobos, like their close relatives the chimpanzees, leave their kin and live as adults with unrelated females. Recent field studies show that these unrelated females hang out together and engage in frequent homoerotic behavior, in which they embrace face-to-face and rapidly rub their genitals together; sex seems to cement their bonds. Examining these studies in the context of my own research has convinced me that one way females use these bonds is to form alliances against males, and that, as a consequence, male bonobos do not dominate females or attempt to coerce them sexually. How and why female bonobos, but not chimpanzees, came up with this solution to male violence remains a mystery.
Female primates also use relationships with males to help protect themselves against sexual coercion. Among olive baboons, each adult female typically forms long-lasting "friendships" with a few of the many males in her troop. When a male baboon assaults a female, another male often comes to her rescue. In return for his protection, the defender may enjoy her sexual favors the next time she comes into estrus. There is a dark side to this picture, however. Male baboons frequently threaten or attack their female friends-when, for example, one tries to form a friendship with a new male. Other males apparently recognize friendships and rarely intervene. The female, then, becomes less vulnerable to aggression from males in general, but more vulnerable to aggression from her male friends.
As a final example, consider orangutans. Because their food grows so sparsely, adult females rarely travel with anyone but their dependent offspring. But orangutan females routinely fall victim to forced copulation. Female orangutans, it seems, pay a high price for their solitude.
Decreasing women's vulnerability to sexual coercion, then, may require fundamental changes in social alliances. Women gave voice to this essential truth with the slogan SISTERHOOD IS POWERFUL-a reference to the importance of women's ability to cooperate with unrelated women as if they were indeed sisters. However, among humans, the male-dominant social system derives support from political, economic, legal, and ideological institutions that other primates can't even dream of. Freedom from male control-including male sexual coercion-therefore requires women to form alliances with one another (and with like-minded men) on a scale beyond that shown by nonhuman primates and humans in the past. Although knowledge of other primates can provide inspiration for this task, its achievement depends on the uniquely human ability to envision a future different from anything that has gone before.