LOS ANGELES, Sept. 26 (Xinhua) -- Researchers recently discovered that a primitive jellyfish sleeps just like humans, challenging the common notion that sleep requires a brain, U.S. media reported.
Researchers from the California Institute of Technology looked at the behavior of Cassiopea, a primitive jellyfish, and found that they show reduced activity, slower responses and need for sleep when deprived of sleep.
The study has proven that a brain is not necessary for sleep. Cassiopea lives upside down on the sea floor and has no central nervous system.
The findings also indicated that sleep is an ancient behavior that stayed unchanged after years of evolution, since Cassiopea is very low on the animal family tree.
The study, published on Current Biology last week, is co-authored by three Ph.D candidates in biology at the institute.
