INFRADIAN RHYTHMS

EVALUATION

Research Support

→ EVOLUTIONARY BASIS

• One strength of menstrual synchrony is that it may be explained by natural selection.

• Synchronisation of the menstrual cycle in a social group is thought by some to have an evolutionary value. For our distant ancestors, this may have been advantageous because newborns who were cared for collectively would increase their chances of survival.

• However, the validity of the evolutionary perspective has been questioned. Schank (2004) argued that too many females cycling together within a social group would produce competition for the highest-quality males (and therefore lower the fitness of potential offspring).

• From this point of view, the avoidance of synchrony would be the most adaptive evolutionary strategy and hence naturally selected.

→ REAL-WORLD APPLICATION

• One of the most effective treatments for seasonal affective disorder (SAD) is light therapy, a box which stimulates very strong light in the body’s internal clock.

• Studies show this helps reduce symptoms of go to 60% of sufferers (Eastman et al, 1998).

• However, the same studies record a relapse rate of 46% over successive winters, meaning some must return for more light therapy treatments.

• This is good for the economy as studies indicate it may reduce reliance on pharmacological treatments (e.g. antidepressants)

Conflicting Evidence

→ METHODOLOGICAL LIMITATIONS

• The limitation of synchronisation studies is the methodological shortcomings.

• The timing of cycle onset (e.g. when it started) can be affected by confounding variables, including stress, changes in diet, exercise etc.

• These may act as confounding variables, which means that any apparent pattern of synchronisation is no more than what would have been expected by chance. This may explain why other studies have failed to replicate the findings.

• This suggests that menstrual synchrony studies are flawed.