The Menstrual cycle

• Female mammals:

– estrous cycle (fertile and in heat).

• Humans & other primates:

– menstrual cycle.

Menstrual cycle vs estrous cycle

• Menstrual cycle:– fertile only on a cyclic basis

– receptive to sex at any time but can only be pregnant at certain times

– fertile period is not synchronized with sexual receptivity.

• Estrous cycle– fertile and heat only at certain times.

– Sexual-receptiveness towards males and fertility are synchronized.