The Balance Between Restorative and Adaptive Functions of Sleep Through Phylogeny and Ontogeny

Sleep is ubiquitous and necessary for virtually any organism with some form of a nervous system. Yet the dominant causes and functions of sleep–and even whether it’s restorative or adaptive–are hotly debated within species, across species, across development, and across daily cycles of night and day. Moreover, a full list of the adaptive functions of sleep, the chunk of time those functions require during sleep, the phase of the sleep cycle during which those functions are realized, and how those different functions contributed to the evolution of sleep as we now know it are all largely still mysteries. Our first working group in 2019 identified some key questions about how these different sleep functions have co-evolved. How do the disparate functions of sleep compete or cooperate? Is sleep a zero-sum game, or can sleep times vary with the needs of individual functions? If the scaling of sleep times across species is set largely by one factor–metabolic rate–how have other sleep functions adapted to this implicit clock? These questions will form the focus of our second working group.