New research has revealed the importance of a circadian body clock that matches the rotational speed of the Earth.
A team of scientists from Holland, Germany and the UK's University of Manchester studied animals in which variation in a single gene dramatically speeds up the natural circadian cycle from 24 to 20 hours.
It is the first study to demonstrate of the value of having an internal body clock which beats in tune with the speed of the earth's rotation.
The researchers released animals with 24 hour or 20 hour clocks into outdoor pens, with free access to food, and studied how the proportion of animals with fast clocks changed in the population over a period of 14 months.
This allowed the team to study the impact of clock-speed in context of the "real-world" rather than indoors.
Mice with fast-running clock gradually become less common with successive generations, so that by the end of the study, the population was dominated by animals with "normal" 24h clocks.
The research has potentially important implications for human health: clock-disruption associated with abnormal work and lighting conditions, such as night shift work leads to health problems, such as increased risk of Type 2 diabetes.
But these studies now extend to the potential implications of space travel in the future. For instance, the Martian day is 37 minutes longer than that on earth.
Professor Andrew Loudon, from The University of Manchester said: "The rotation speed of Mars may be within the limits of some people's internal clock, but people with short running clocks, such as extreme morning types, are likely to face serious intractable long-term problems, and would perhaps be excluded from any plans NASA has to send humans to Mars.
"The prospect of settling on Mars is a somewhat distant prospect.
"But if we ever do get to the Red Planet, I suspect we will be faced with body clock problems; those people with abnormally slow body clocks would be best suited to living there."
He added: "A correctly ticking body clock is essential for normal survival in the wild, and this has to be in phase with the rotation speed of the earth.
"Animals with clocks that do not run in synchrony with earth are selected against.
"Thus, the body clock has evolved as an essential survival component for life on earth."
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