Gibbons are the one nonhuman primate closely related to humans that exists with an apparent monogamous mating relationship and a family-unit form of social organization. Moreover, these animals represent an endangered species that have not been adequately studied. Using a semi-natural environment, Dr. Nadler will carry out a series of studies on gibbon reproductive endocrinology, stress and behavior. The research program integrates evolutionary, functional and mechanistic issues and approaches at several levels including physiology, behavior and taxonomy. This work is of great importance in discerning the possible origins of human behavior. The ideas fostered by this research may lead to a better understanding of the nature of monogamy in primates and with respect to possible parallels to human mating systems. Moreover, information about reproductive physiology on gibbons is critical for the conservation and maintenance of this endangered species. Finally, given their close biological relationship, information gained from this work is of potential value in elucidating the interactions between reproductive hormones and behavior in humans.