We have now considered three powerful motives: thermoregulation, hunger, and responses to threat. In each case, we have discussed mechanisms that we share with other creatures (e.g., the autonomic responses associated with body temperature regulation, homeostatic regulation of blood sugar, the biological response to threat), and in each case, the adaptive function roots of these mechanisms are easy to discern. In addition, we have seen that these genetically rooted mechanisms are powerfully influenced by learning and culture (e.g., the fashions that dictate the clothes we wear, the implicit rules that determine what we eat, and the cultural practices that govern how we respond to provocation).
These motives are all very well and good, but you wouldn’t even exist without another crucial motive, namely, sex. This motive is unmistakably rooted in our physiology just as thermoregulation, hunger, and the response to threat are. In some ways, however, sex is different. Unlike the other biological motives, sex is inherently social, and in humans its pursuit is intertwined with all manner of cultural patterns and attitudes.
Let us start our discussion with the aspects of sexual behavior that are most obviously biological—mating itself and the role of hormones in controlling an organism’s behavior. We will then turn to aspects of sexual behavior for which the influence of biology, and of evolution in particular, is still hotly debated, touching on some of the topics, in our broader discussion of evolution.