limitations

• Morgan's research is flawed due to its use of hamsters as subjects
• Humans are very different biologically, cognitively and socially from hamsters

  • This means that research using hamsters is not generalisable to humans
  • The role of endogenous pacemakers in humans therefore cannot be explained using animal research
• It is biologically reductionist to focus on a narrow range of explanations when considering something as complex and prone to variation as the patterns and habits involved in the sleep-wake cycle
• There are likely to be an array of other factors which also contribute to circadian rhythms which may supersede the endogenous pacemaker explanation
• • high-stress levels may interfere with regular sleep
  • some people can (and may frequently) fall asleep in bright light, or during daylight hours which means that light may not be as important to the sleep-wake cycle as some research suggests