Circadian Rhythms

About ten years ago we held a Mystics and Scientists conference on cycles and rhythms, since which time a great deal more research has been carried out, as described in this excellent 'Very Short Introduction'. Nearly every living thing uses internal biological clocks to anticipate changes in light and temperature and adapt their physiology and behaviour accordingly - all this can confer an evolutionary advantage. There are differing 'circadian chronotypes', which also vary depending on age. The fact that the rhythm of someone in their late teens is delayed by around two hours compared with an individual in their 50s accounts for what the authors call 'social jetlag' so that asking a teenager to get up at seven in the morning is the equivalent of asking the 50-year-old to get up at five. As all parents will know, 'teenagers are biologically predisposed to get up late and go to bed late', a trend that has been exacerbated by ubiquitous technology. The authors describe and recent research on the 'molecular clock' as well as the latest on sleep and metabolism. When it comes to seasons, some animals hibernate over winter, and apparently a chipmunk can reduce its body temperature to 0°C and change its rate from 350 beats a minute to as low as four. I was fascinated to learn that 65% of all bird species migrate and exhibit typical behavioural and physiological changes as a result. In our own case, almost a quarter of our genes show different activity according to the time of year.