Scientists: Is Sleep Essential?

Writing in the latest PLoS Biology, researchers from the University of Wisconsin, Madison are wondering whether sleep is really a biological necessity, or maybe it’s just a function created by evolution to kill time and avoid stress.
From the article in PLoS Biology:

Everybody knows that sleep is important, yet the function of sleep seems like the mythological phoenix: “Che vi sia ciascun lo dice, dove sia nessun lo sa” (“that there is one they all say, where it may be no one knows,” Wolfgang Amadeus Mozart and Lorenzo da Ponte [1790], Così fan tutte). But what if the search for an essential function of sleep is misguided? What if sleep is not required but rather a kind of extreme indolence that animals indulge in when they have no more pressing needs, such as eating or reproducing? In many circumstances sleeping may be a less dangerous choice than roaming around, wasting energy and exposing oneself to predators. Also, if sleep is just one out of a repertoire of available behaviors that is useful without being essential, it is easier to explain why sleep duration varies so much across species. This “null hypothesis” would explain why nobody has yet identified a core function of sleep. But how strong is the evidence supporting it? And are there counterexamples?
So far the null hypothesis has survived better than alternatives positing some core function for sleep [8–10]. In what follows we shall test the null hypothesis by considering three of its key corollaries. If the null hypothesis were right, we would expect to find: (1) animals that do not sleep at all; (2) animals that do not need recovery sleep when they stay awake longer; and, finally, (3) that lack of sleep occurs without serious consequences.

Article in PLoS Biology: Is Sleep Essential?
Check out this illustration from the article that lists animal species in which the presence of sleep and/or Its homeostatic regulation have been called into question…