Animals Needed Sleep Before They Even Had Brains

A study of hydras, which are small creatures that live in freshwater environments and have no central nervous system, suggests that animals’ need for sleep likely predated the evolution of brains. “Many questions still remain regarding how sleep emerged in animals, but hydras provide an easy-to-handle creature for further investigating the detailed mechanisms producing sleep in brainless animals to help possibly one day answer these questions,” said Taichi Itoh, one author of the study in Science Advances.