Why do we sleep? New theory attempts to answer it

**brother** · #1 08-26-2009, 11:47 AM

The purpose of sleep remains one of the greatest unsolved mysteries in science. Although we spend roughly one-third of life asleep, researchers still do not know why.

While sleep is often thought to have evolved to play an unknown but vital role inside the body, a new theory now suggests it actually developed as a method to better deal with the outside world.

Sleep is often seen as bad for survival. Sleeping animals might be vulnerable to predators and cannot eat, mate, scout for prey, care for relatives or perform other behaviors key to getting by. As such "it's been thought that sleep must serve some as-yet unidentified physiological or neural function that can't be accomplished when animals are awake," said sleep researcher Jerome Siegel at the University of California at Los Angeles.

However, Siegel noted that a number of species could make do without sleep for long spans of time.

For instance, newborn dolphins and killer whales and their mothers show an almost total lack of what might be called sleep in other animals - that is, extended periods of immobility - for several weeks after birth, when these animals normally migrate. Similar findings are seen in birds during migrations, "where birds can fly for days on end without stopping," he explained.

"So you have to start thinking - if sleep has a vital universal function, how are they able to survive without it?" Siegel said.

Carnivores get their zzzz's

In a survey of the sleep times of a broad range of animals, Siegel found that carnivores sleep more than omnivores, which in turn sleep more than herbivores. To him, this suggested the role of sleep was linked to an animal's niche in its ecosystem.

One example Siegel cited was the big brown bat, which sleeps 20 hours a day, perhaps the record for mammals.

"One might suppose this animal sleeps so much because of some unknown function that sleep has for it," Siegel said. "But it seems more easily explained by the fact that it preys on moths and mosquitoes that only come out at dusk and are active for only a few hours before the temperature falls and they can't function. If it spent more time awake, it would spend more energy but not be as successful at hunting, and if it came out in the day it would be exposed to predatory birds that can see much better than it can."

Siegel proposes the main function of sleep is to increase an animal's efficiency and minimize its risk by controlling how a species behaves with regards to its surroundings.

Read the full article at New Theory Questions Why We Sleep - Yahoo! News