Thank you for downloading this episode of In Our Time for more details about In Our Time

and for our terms of use, please go to bbc.co.uk slash radio4.

I hope you enjoy the program.

Hello, circadian rhythms are a biological version of a clock inside humans and all other

animals and they're in plants and quite possibly in almost every living cell.

The origin can be traced back to the beginning of life itself three and a half billion years

ago.

These rhythms are a response to the most predictable condition of life on Earth, that is, dark

at night and bright during the day.

For billions of years life has depended on circadian rhythms to ensure the best use of daylight

hours and to promote rest in the darkness when cell repairs and memory adjustments can be

carried out for the next day.

Daylight regulates the clock.

In modern times has been increased interest in the effect of artificial light on humans

and whether that can disrupt our circadian rhythms and disrupt our sleep with grim consequences

for health.

What we do discuss circadian rhythms are, Russell Foster, the professor of circadian neuroscience

at the University of Oxford, Deborah Schien, professor of neuroendocrinology at the University

of Surrey and Steve Jones, emeritus professor of genetics at University College of London.

Steve, circadian rhythms first.

Well, it's all in the name, circadian almost a day and a circadian rhythm is any biological

process on any level from biochemistry to human behavior which has an approximately 24

...