The Menstrual Cycle: Infradian Rhythm

• What is the role of circadian rhythm in humans?

  It regulates the sleep-wake cycle
• What does the term "circadian" mean?

  It means around the day
• What does "infradian" refer to?

  A rhythm below the frequency of once a day
• What does "ultradian" mean?

  A rhythm occurring more than once every 24 hours
• What is the most obvious biological rhythm in humans?

  • The menstrual cycle
  • A female cycle of fertility
• What is the average length of the menstrual cycle?

  28 days
• What biological changes occur during the menstrual cycle?

  Releasing the egg and thickening of womb lining
• Which hormones regulate the menstrual cycle?

  Estrogen and progesterone
• What are endogenous pacemakers?

  Internal body clocks regulating biological processes
• What did McClintock's 1971 research find about menstrual cycles?

  Women synchronized their cycles in dormitories
• What did Russell's 1980 research suggest about synchronization?

  It could be due to shared pheromones
• What did Stern's 1998 study involve?

  Women using pads from donor women's armpits
• What was the conclusion of Stern's study?

  Synchronization was influenced by pheromones
• What are the criticisms of pheromone synchronization theory?

  • Many studies failed to replicate findings
  • Variability in menstrual cycles not considered
  • Conflicting evolutionary arguments
• What is the evolutionary argument for menstrual synchronization?

  It prevents one male from dominating reproduction
• What is the argument against synchronization being adaptive?

  Women may want to mate with the best genes
• What historical belief is associated with menstrual cycles?

  They were controlled by the phases of the Moon
• What did the study of 1.5 million women find about menstrual cycles and the Moon?

  No link between cycles and Moon phases
• Why is the relationship between menstrual cycles and the Moon considered correlation not causation?

  There is no direct cause established
• What is the implication of the chimpanzee cycle length in relation to human cycles?

  It shows no evolutionary advantage in synchronization