From a behavioral point of view, sleep could be considered as a “simple” rest. One can easily understand that, when there is nothing to do or when environmental factors are not beneficial, sleep could be an excellent way to save energy. But, interestingly, when the need arises to be active for a prolonged period of time, why can an organism not resist the irremediable pressure to sleep? Why do all animals experience this daily rest, unconscious from their environment, and often times exposed to predation?

     Conserved over millions of years of evolution, this would certainly mean that sleep serves a core function. But what function? Or what functions? Is the role of sleep the same for each species? In addition, how was this universal and apparently essential behavior selected for by natural selection?

      One way to understand why we all sleep is to look at the diversity of the sleep phenotypes across species with different morphologies, life styles, diets, and ancestry … and try to make parallels, comparisons, and correlations. An evolutionary perspective through studies of the current diversity of sleep phenotypes is key to have a better and more complete understanding of what sleep is and of why all animals sleep.

     In order to quantify the sleep phenotype under natural conditions in the wild, we have developed a unique expertise in collaboration with the biosensor team of the Nanotechnology Institute of Lyon. We are currently able to record running, flying, and swimming species weighting less than 50g for days or weeks.