Chapter 1
Chapter 2
Chapter 3
Chapter 4
Chapter 5
Chapter 6
Chapter 7
Chapter 8
Chapter 9
Chapter 10
Chapter 11
Chapter 12
Chapter 13
Buy the book
We watch the sun rush up from the East, pass over our heads, and sink into the West, like a great celestial tennis ball, but one that goes over an imaginary net in only one direction. Helped by the biologist friend who is watching with us, we begin to notice more. We notice that the leaves on the trees also seem to have a pattern: they move differently as the day passes – some open during the day, close at night. Just as we are beginning to feel quite pleased with our powers of observation, a biologist gently points out that a Frenchman named de Mairan , who was not even a biologist, but an accomplished astronomer, had also noticed the same thing (without using a high-tech camera) in 1729.
All animals, including humans, have a daily body programme that follows a remarkably consistent pattern. The day (or night) is full of different bodily events, all in the right sequence, and happening at the right time. In some cases - for example the digestive processes that follow a meal - the sequence of events depend upon each other, rather than upon an external synchronising signal. In others, there is a direct link between the synchronising signal (the sun). This means that different events must have a different lead time: for example, if your lunch is linked to sunrise, then your body has to have some means of assessing the passage of time, so that lunch occurs at lunch-time, not earlier..... This implies, of course, that animals (and humans) can measure
the passage of time quite
accurately without looking at an external clock…Since the limbic system controls eating, drinking, hormones, the cardiovascular system and many other elements making up the daily programme, it seems likely that the clock, if there is just one, might also be somewhere in this part of the brain. Let’s focus a bit more: the hypothalamus is the part of the limbic system that monitors the internal environment, and thus the daily surges of physiological activity. So perhaps we should look in the hypothalamus. Despite what now may seem rather obvious, it took until 1972 for Friedrich Stephan and Irv Zucker, working in the USA, to do the essential experiment: they found the clock…..
….in countries appreciably distant from the Equator, the young of nearly all wild species are born in the spring. The reason is obvious: reproduction , a biologically and socially expensive and risky business (we talk more about this in Chapter 8) needs the very best conditions to ensure that the young survive. Most animals can’t afford to breed throughout the year: they have to ‘choose’ the best season.... So to ensure that the young are born at the right time, animals have to mate at the ‘right’ time, which will differ depending on the duration of pregnancy (for that particular species). Which presents us with another adaptive problem: how on earth do animals know when spring will come? Or when its here? How do different species mate at the right (different) time? The annual baby-boom in the spring clearly shows us that they must do it somehow. Luckily, they have a means: if they could measure daylength (as opposed to the time of day) they might be able to compute the time of year. …
Rhythms represent regularities in behaviour and physiology which form essential adaptive responses to a regularly changing environment. These adaptations must be flexible: though the light cycle stays the same each year, other important elements in the environment, such as food supply or temperature, are not nearly so reliable. So it’s not surprising that both circadian and annual cycles can be modulated by factors other than light. Animals living at different latitudes also need to be able to adapt: for example, breeding in foxes living in more Northern regions begins later than in the same species nearer the Equator. The limbic system makes sure that the internal and external environments stay in concert with one another. Your body dances to the music of time.
Scientific and literary quotes.