HORMONES AND NEUROTRANSMITTERS help shape important aspects of our lives, including growth, differentiation, sexuality, physiology, emotion, and cognition. From romantic thoughts to jealous rage, from the release of gametes to lactation and parent-offspring bonding, the extraordinary molecules produced and released by tiny and otherwise seemingly insignificant cells and glands orchestrate our reproductive strategies. A key research objective is to understand the evolutionary functions of this chemical language. Endocrine and neuroendocrine systems may be viewed as complex sets of mechanisms designed by natural selection to communicate information among cells and tissues. This chapter focuses on an area of particular importance for evolutionary psychology: the behavioral endocrinology of the human family. Steroid and peptide hormones, associated neurotransmitters, and other chemical messengers guide mating and parental behaviors of mammals in many important ways (Curtis & Wang, 2003; Rosenblatt, 2003; Young & Insel, 2002). Cross-species comparisons among primates require careful analysis (Bercovitch & Ziegler, 2002) because of the apparent rapid evolutionary changes in patterns of reproductive behaviors and increased phenotypic flexibility involving intricate mental processes. Homo sapiens presents special problems in these regards (Fisher, 2004; Maestripieri, 1999; Marler, Bester-Meredith, & Trainor, 2003; Wynne-Edwards, 2001, 2003). Here we first provide a theoretical scenario for the evolution of human patterns of mating and parenting behaviors. We test our model by examining the phylogenetic trajectories of associated traits such as sexual dimorphism and life history stages from the hominin fossil record. We then turn to a description and functional analysis of the endocrine mechanisms that may influence these remarkable reproductive behavioral characteristics of our species.
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