The Science of Sleep (and the Lack Thereof)

From PLoS Biology, a paper which asks the question Is Sleep Essential?

The authors find that there is no solid report of an animal that does not sleep at all. The bullfrog is often cited as an example of a sleepless animal, but the evidence is old and needs revisiting.

Dolphins sleep half a brain at a time (one hemisphere sleeps while the other stays awake). This strongly suggests that sleep is important (and not just a type of resting). Why else would such a complex mechanism have evolved?

In general, reading this paper, it’s surprising how little we understand about sleep. Should we still be arguing whether animals sleep?