AO3 - Infradian Rhythms

• Research to contradict that infradian rhythms are mainly governed by an endogenous system was conducted by Russell. They asked a sample of women to wear cotton pads under their arm, which were then rubbed on the upper lip of 5 sexually inactive women. This was repeated daily for 5 months. They found that 4/5 women developed menstrual cycles that synchronised to within one day of the donor's. Therefore, suggesting that the infradian rhythm of the menstrual cycle can be affected by exogenous factors as well as controlled by endogenous factors which may influence the length of the rhythm.
• However, Russell’s research was a field experiment and so has low control over extraneous variables. The research took part in the participant’s natural environment, where other exogenous factors, such as light, changes in diet and stress, could also have affected the infradian rhythm. Therefore, it is difficult to establish cause and effect between the influence of pheromones on maintaining an infradian rhythm. This weakens the extent to which Russell’s research can contradict the importance of endogenous pacemakers on maintaining infradian rhythms.
• However, despite the methodological flaws in infradian synchronisation studies, the research findings can be explained by evolutionary psychologists. It would have been advantageous in our evolutionary past for a social group to synchronise pregnancies so that many women would be breast feeding at the same time so one mother could take over caring for an orphaned child, to improve chances of survival. Therefore, showing that synchronisation of infradian rhythms, such as the menstrual cycle, is an adaptive strategy and supports exogenous factors influencing infradian rhythms.