Processing of environmental stimuli and primate reproduction

The prosimian primates have much in common with the non‐primate mammals in that reproduction is strictly limited by the physical environment. This determines the onset of the ovarian cycle which in turn synchronizes reproductive behaviour with ovulation. In simian species (monkeys and apes), however, the reproductive cycle does not directly depend on such environmental factors as temperature, rainfall or day length. Indirectly, of course, such factors exert an influence in so far as they dictate the nature of the habitat which in the long term has shaped social organization and in the short term determines the availability of food. It is through these factors, social organization and food availability, that the physical environment determines the timing of reproduction. The seasonal onset of reproductive cycles is principally related to the changing nature of mother‐infact interactions, which in annual breeders is influenced by the availability of food. This availability depends in part on climatic conditions, but also on social status: high rank determines priority of access to food, so that dominant females resume cycling after giving birth earlier than do females of low rank. Another way in which social status operates to enhance the reproductive success of animals that achieve high rank is by the suppression of sexual behaviour in subordinate males and inhibition of fertility in low‐ranking females. Of importance in this context has been the emancipation of reproductive behaviour (proceptivity/receptivity) from strict gonadal control. The degree to which this emancipation from both the external, physical environment and the internal, gonadal environment has been made possible is related to the growth of the neocortex and its domination of the limbic brain.