Infradian rhythms

• Infradian rhythms are cycles that last longer than 24 hours.

  For example, the menstrual cycle.

  The function of the menstrual cycle is to regulate ovulation and this is controlled endogenously by the hormones oestrogen and progesterone
• The menstrual cycle 


  • Lasts between 27-35 days, typically 28.
  • Oestrogen is released by the ovaries and is involved in the preparation & release of the egg.
  • Ovulation occurs halfway through the cycle when oestrogen levels peak (lasting 16-32 hours).
  • After ovulation, progesterone levels rise, causing the lining of the womb to thicken for fertilisation
  • If fertilisation doesn't occurs, the lining & egg are shed (menstruation 🩸) and the cycle begins again
• The menstrual cycle is mostly controlled internally, evidence shows that exogenous zeitgebers play a part too.

  It is suggested that women's menstrual cycles can be affected by the pheromones of other women and cycles become synchronised
• Research support AO3

  Russell et Al 


  Russel directly tested the effect of pheromones

  • Gathered sweat 😅 samples from the armpits of a donor female by placing cotton pads under her armpits for 24 hours.
  • The cotton pads were then rubbed on the lips 👄 of 5 female pots
  • This happened 3x a week for 6 months. At the end, all but one of the ppts and synchronised cycles with the donor female.
• Russell's study was a controlled lab experiment and seemed to demonstrate clear evidence 🧾 of the effect of pheromones. However, it's claimed synchronised cycles are a myth and it is no more likely than would be expected by chance.

  Furthermore, many studies that support this use small samples and rely on women recalling the onset date 📅 of menstruation 🩸, so may be inaccurate

  • Other studies of synchrony have also failed to replicate these findings
• AO3 An evolutionary advantage of menstrual synchrony 


  Turk et Al believe there is an evolutionary explanation for why menstrual synchrony is advantageous

  For our ancestors, it was beneficial for females to ovulate together so they would then fall pregnant 🤰 together. This would mean that their offspring could be cared for collectively , e.g. if mother died, increasing their chance of survival
• AO3 - real world application

  The menstrual cycle has been the subject of psychological research due to the behavioural changes often linked to it, e.g.- mood swings, irritability.

  As a result, improving the understanding of biological rhythms has led to PMS (pre menstrual stress) being considered a psychological event out of an individual's control

  This has led to severe PMS being used as a valid defence in major crimes where witnesses have successfully argued that it's akin to a mental disorder sso individuals should not be held responsible for their actions (e.g. Ms English, 1987)
• AO3 - arguably an over deterministic approach 


  There is evidence that we can "will" our biological rhymes to change.

  • One study found people who were told to wake up earlier than usual had higher levels of ATCH (involved in the waking process) and they did wake up earlier than normal at the designated time.
  • Suggesting rhythms aren't beyond our control and so questions the appropriateness of these defense claims