To understand monogamy s place in human evolution, primatologists have sought out clues from our closest relations, monkeys and apes. The savanna s long vistas allowed for easy behavioral observation by the early primatologists of the 1950s and 60s. But as the primatological record has become more complete, researchers have discovered a wealth of other social systems. Even among the generally gregarious great apes, one species the orang utan flies solo. And it is only in the orang utan, this unusually asocial primate, that forced mating is commonly observed.
Sex roles can flip in primates too.
In a few rare instances, females themselves rule the roost. Nowhere is this trait more common than on the island of Madagascar, where female lemurs reign supreme. Ring-tailed lemur females assert their preeminence aggressively, driving males away from cherished fruits and tamarind pods. Female sifaka lemurs, however, dominate without a fight. Sifaka females give birth during the dry season, when little food is available.