Uncovering the evolution of sleep with the help of the hydra

Why do we sleep? Primarily so our brain can rest, recharge and cleanse itself, right? Following this logic, it would make sense to assume that sleep developed as behavior after our brains evolved to be large and complex enough to need it.   However, a new research collaboration led by Taichi Itoh (Kyushu University, Fukuoka, Japan) has discovered sleep-like states in Hydra; simple, water-dwelling animals with no brain. The team even displayed that hydras respond to the molecules associated with sleep in more complex animals with brains. These findings indicate that sleep developed before the brain and may have key functions outside of the brain.  Exploiting their simple composition and lack of a complex central nervous system, the team selected hydras to...