In the preceding chapters, processes with a greater degree of autonomy, such as growth, maturation and ageing, were examined. This chapter and the next examine sexual communication and the effects of procreational biology on the foundation of social structure. To effectively synchronize social interactions an animal needs both the ability to send information to others and the capacity to receive (and correctly interpret) signals from others. Both aspects of communication must evolve together and involve co-ordinated nervous and hormonal interactions. Reproductive behaviour has its origin in genetic coding, but its final expression is vulnerable to modifying epigenetic influences and past history. The extent to which our behaviour follows the dictates of our genes or is the expression of conscious inventions of our thinking brains is not known, but it is the subject of much controversy. Many behavioural patterns, for example, feeding, sleeping and breathing, are essential and recur throughout our lifespan. Other behavioural patterns, not essential for individual survival, are brief and may occur rarely or even only once in a lifetime but still have great significance. Such patterns may include parturition, lactation or even copulation. The first coitus is usually a milestone in the psychosocial development of an individual as it represents a critical, dynamic conjunction of two bodies. Copulation co-ordinates, through a complex series of neuroendocrine events, the transition between two major life stages, prereproduction and reproduction. The co-ordination of the behavioural aspects again represents the interaction of another complex series of neuroendocrine events. Gamete production can proceed in total social isolation, but the production of viable young (ignoring IVF technology) requires social exchanges.