Our internal body clock is timed by weather and the seasons, a new British study has confirmed.
The study fronted by researchers from the University of Edinburgh used computers to simulate the working of the human body clock.
The BBC quoted Dr Carl Troein, of the University of Edinburgh's School of Biological Sciences, as saying: "By better understanding why biological clocks are so complex, we stand a better chance of controlling them.
"Our study goes some way to explaining how and why these in-built rhythms have developed. We hope it will be useful in informing treatments for sleep disorders as well as helping scientists develop crops that can survive in the long term."