FERTILITY AND A MATES SIGNALS OF CONTINUED PRESENCE

a system by which males send, and females receive, evidence of the mal e's continued presence is hypothesized. Such a system would promote th e fitness of both sexes. Females increase their fertility when they ca n anticipate a mate to help rear the child. The existence of such a sy stem could explain amongst others the following observations: that the menstrual cycle is more often of a fertile type when there is regular intercourse, that exposure to males influences ovulation, the large a mount of non-reproductive sexual activity, the presence of what may be a functional vomeronasal organ, and the apparent design of the axilla for emitting odors or pheromones.