Stern and McClintock

• Stern and McClintock: The menstrual cycle was once thought to be regulated wholly internally, by the hypothalamus (the endogenous pacemaker).
• However, evidence suggests that external factors (zeitgebers) can play a role in ovulation and menstruation
• It is thought that women at different stages of the menstrual cycle give off different pheromones
• McClintock and Stern’s findings show that the menstrual cycle is influenced by these zeitgebers, and explain to an extent how women’s menstrual cycles can come to synchronise