Evolution and plasticity of sleep

Sleep is a highly conserved state across the animal kingdom. However, sleep duration, behavior and associated neural activity show great diversity across taxonomic groups, and sometimes even within the same species. Understanding sleep functions depends on understanding when sleep emerged, which of its characteristics have persisted throughout evolution, and what accounts for the similarities and differences in sleep behavior and neurophysiology across different species. Here, we provide an overview of the latest findings in comparative sleep neurophysiology and highlight remarkable examples of sleep flexibility. We discuss the implications that these findings have on the proposed functions of sleep.