Why do we sleep? Because we have nothing better to do.

An interesting article on the purpose of sleep has just been published. According to the article, lots of reasons for sleep have been proposed, but when looking at the animal kingdom as a whole, none of them holds up as a reason for why we do it. The article proposes that instead of evolving for the purpose of immunological function, hormonal regulation, or memory synthesis, sleep exists to optimize energy conservation.

The example of the brown bat is used, which sleeps for 20 hours a day. Why does it sleep so much? Because its prey is only available during a short window of time, and to be active outside of that window would be using energy with no ability to catch food to offset the expenditure. Being more active would also leave the bat more vulnerable to predation from birds. So if there is no benefit to being awake and active, why not sleep? I think we can all relate to this idea. How many lazy summers as a kid did we spend sleeping excessively solely because we had nothing else to do?

This has interesting implications for those of us interested in polyphasic sleep. There is very little real science that has been done so far on the topic, but there are quite a few blogs out there by people who have tried it. One theme that crops up again and again is people struggling with or giving up on the polyphasic lifestyle due to having "nothing to do" with those extra hours. I maintained a polyphasic sleep cycle for a few months in Seattle, and a common question by friends was "Why would you do that? What would you do with the extra time?"

If we sleep because we have nothing better to do, the answer seems intuitively obvious: find something better to do.