Socioendocrinology is the study of the effect of the social environment on the interactions between hormones and behavior. Individuals have evolved a physiological flexibility that enables them to respond to their social surroundings in a manner that maximizes reproductive success. We present evidence that (a) males who have evolved to participate in infant care have different endocrine profiles around offspring from males who have not evolved to regularly participate in infant care, (b) the energetic costs of reproduction in both males and females creates conditions conducive to elevated levels of both stress and sex hormones, (c) adolescent subfecundity among females evolved as a mechanism fostering mate choice, (d ) some primate species are probably facultative ovulators, and (e) endocrine suppression of subordinate males probably does not contribute to delayed onset of reproduction but does contribute to reduced access to females, which hampers progeny production. Hormones and behavior are inextricably intertwined in a feedback relationship that regulates each other.
