AO3

• A weakness is that it has been argued that the synchronisation of female menstrual cycles could be

  -In the EEA, if females menstruated together, there was a greater chance they would fall pregnant and have their offspring at a similar time.

  -This would mean that the new-borns could be cared for collectively, thus increasing the chances of the off-spring’s survival.
• However, it has been argued that this evolutionary perspective lacks validity.

  -Schank (2004) suggests that if too many females had synchronised cycles it would increase the competition for highest quality males and potentially lower the fitness of any offspring. This suggests that avoidance of synchronicity would be the most adaptive strategy. 
• Another weakness is that this study has been criticised for various

  -methodological issues. Firstly, there are several factors that can affect a women’s menstrual cycle, including stress, diet and exercise etc., these could act as confounding variables. 

  -Additionally, many of the research studies have involved small sample sizes of women and relies on self-report techniques for the onset of their own cycles.
• A strength is that this has led to treatments for SAD like

  -phototherapy

  -This is a light box that stimulates very strong light in the morning and evening. It is thought to work by resetting the melatonin levels in people with SAD. 

  -Eastman et al. (1998) found that it relieves the symptoms in 60% ofsuffers.
• A strength of the sleep cycle is that studies have found REM to be highly correlated with dreaming

  -Dement and Kleitman monitored the brain waves on nine adult participants in a sleep lab. Brain wave activity was recorded on an EEG and the researchers controlled the effects of caffeine, and alcohol.

  -brain activity varied depending how vivid the dreams were, and when participants were woken during dreaming, they were able to report their dreams more clearly.