A03 Biological Rythms: Infradian And Ultradian Rhythms

• Evolutionary basis of the the menstrual cycle


  Menstrual synchrony is thought to by many to have an evolutionary value. For our ancestors it may have been advantageous for females to menstruate together and therefore fall simultaneously pregnant, meaning that new-borns could be cared for collectively in a social group; increasing the chances of offspring's survival.
• Questioning valdidity of evolutionary theory (Evolutionary basis of the the menstrual cycle)


  Schank argued that if there were too many females cycling together within a social group, this would produce competition for the highest quality males; thereby lowering fitness of any potential offspring. From this point of view, the avoidance of synchrony would appear to be the most adaptive evolutionary strategy and therefore naturally selected.
• Methodological limitations in synchronisation studies

  There are criticisms of early sycnhronisation studies and methods emploted. Many factors effect changes in women's menstrual cycle like stress and changes in diet. They are confounding variables and therefore, any pattern of synchronisation is no more than would have been expected by chance. Research also involves small samples and relies on self-reporting on own by eye.
• Evidence supports the idea of distinct stages in sleep

  Dement and kleitman monitored sleep of nine adult ppts in a sleep lab. The brainwave activity was recored on an EEG and researchers controlled for effects of alcohol and caffeine. REM activity was highly correlated to dreaming and brain activity varied based on how vivid the dream was. Replications noted similar findings too.
• Animal studies


  Much of the knowledge of the effects of pheremones on behaviour is derivred from animal studies. The role of pheremones in animal sexual selection is well documented like sea urchins releasing pheremones into the surrounding water so other urchins in the colony will eject their sex cells simultaneously. But the evidence for the effects in human behaviour remains speculative and inconclusive.
• Practical application to SAD

  One of the most effective treatments for SAD is phototherapy

  which his is a light box that stimulates very strong light in the morning and evening. It is thought to reset melatonin levels in people with SAD. This relieves symptoms in up to 60% of sufferers.
• Opposing evidence (Practical application to SAD)

  However, the same study recorded a placebo effect of 30% using a sham negative ion generator (participants were told it was another form of treatment).This casts doubt on the chemical influence of the phototherapy