The authors present data on the factors governing sexual behavior in female guinea pigs (they have previously done the same for the male guinea pig). They clearly demonstrate that prepubertal social contact with animals of the opposite sex is necessary for optimal development of sexual behavior in female as well as in male guinea pigs. They quote similar results in the studies of male and female chimpanzees, and conclude that experiential as well as hereditary factors are clearly important in determining sexual behavior in all these species. Prior to these studies the sexual behavior of these animals was assumed to be instinctive in the sense of being hereditarily determined and unlearned. It was also demonstrable in this study that exposing the prepubertal guinea pigs to the learning situation had a greater effect than if the exposure was postponed until after puberty.