As a father of two dawn-loving children I don’t get as much sleep as I used to, which makes me wonder sometimes why I crave it so much. A number of scientists who share my curiosity have turned to sleeping animals to find an answer. Sleep appears to be an ancient behavior, perhaps 600 million years old or older. But it may not exist “for” any one purpose. Instead, sleep can serve many functions, as animals are shaped by evolutionary tradeoffs. I’ve written an article about the evolution of sleep for tomorrow’s New York Times where you can read more. (And for those interested in some of the the gorey technical details, here’s an interesting new review in Nature