Describe and Evaluate Research studies into Infradian Rhythms (24 marks)
Infradian Rhythms repeat themselves over a greater period of time – rhythms that last longer than a day. For example, they may repeat themselves weekly, monthly or even annually (known as a circannual rhythm), for example, hibernation, bird migration and many reproductive cycles. As an example of a human biological Infradian rhythm, take the menstrual cycle.
Several research studies have been done into Infradian rhythms, and how to regulate them. Infradian rhythms are governed by endogenous pacemakers (internal cues) and exogenous zeitgebers (external cues). One zeitgeber that helps regulate Infradian rhythms is the release of pheromones; a biochemical substance produced in the endocrine system and distributed throughout the blood, which is then released into the air which often affects other individuals.
Research into exogenous zeitgebers was carried out by Russell (1980) who used pheromones to synchronise women’s periods within a small group. He took the pheromones of one woman and applied them to a group of sexually inactive women by taking cotton pads that had been in the woman’s armpit and rubbing the cotton pads onto the group of women’s upper lips. By the end of the experiment, 4 out of 5 women in the experimental group had menstrual cycles that synchronised within 24hours of the donor’s, as opposed to none in the control group. This suggests suggested pheromones act as exogenous zeitgebers and can influence endogenous pacemakers.
Russell’s research has empirical support from McClintock & Stern (1998) who set up a 10-year longitudinal follow-up study of Infradian rhythms, following Russell’s research using a bigger sample of 29 women with a history of irregular periods. It was found that 68% of women responded to the pheromones and their menstrual cycles changed dramatically up to 14 days to match the other synchronisation.
On the other hand, these results can be explained as random occurrences and do not form a significant difference statistically. This is shown how in a study testing a women’s basketball team for an extended period, there was no correlation found between menstrual cycles suggesting it could be that dieting, exercise and stress could all play a role as unaccounted variables, reducing the internal validity of Russell’s study.
Alternatively, Turke believed however there to be an evolutionary significance to synchronised periods allowing women living together to share child-caring duties. This would fit in with the evolutionary approach…