It seems like something too obvious to question – surely all animals sleep? Perhaps not exactly like we do, but they must have some sort of ‘shut down’ state! Right? Well…
Jerome Siegel is a Professor at the Brain Research Institute at UCLA, and he has contributed tremendously to our understanding of sleep and dreaming. He wrote a review, published in 2008, where he asked this exact question. Before we get into the really interesting bits, I’d like to point out how much I enjoyed reading Siegel’s article. It’s well written, and has a certain cheek to it. The main point (to avoid killing you with suspense) is that the assumption that all animals exhibit a state recognizable as ‘sleep’ might not be as sound as many of us believe. The article is divided into sections, each dealing with a class (more or less) of animals. Siegel gives an overview of the studies that have looked at ‘sleep’ in that class, which might come to ten or so articles (if that). Siegel then ends with a statement like:
There are more than 30 000 species of fish.
I cracked up every time.