The sleep behaviour of jellyfish and sea anemones appears strikingly similar to that of humans. These ‘primitive’ organisms need around 8 hours of sleep per day, just as humans do, and during sleep the DNA damage that accumulates whilst the animals are awake is reduced. With these conclusions, Israeli neurobiologists lend support to the hypothesis that sleep evolved to reduce DNA damage – particularly in neurones (Nature Communications, 6 January). The emergence of sleep is thought to have coincided with that of a form of nervous system, which first appeared in animals closely resembling present-day jellyfish and sea anemones. These animals have no brain, but do possess a relatively simple nerve net.
By monitoring movement, the researchers established that Cassiopea andromeda jellyfish sleep primarily at night, whilst the sea anemones studied (Nematostella vectensis) rest mainly during the day. When the animals experience sleep deprivation, they accumulate more DNA damage. As compensation, they subsequently sleep more, after which the damage does indeed decrease. Jellyfish and sea anemones also deploy this compensatory mechanism when researchers induce DNA damage using UV radiation.