According to a new study, sleep evolved before brains did. Researchers found this out by studying a small freshwater creature called a hydra that appeared to be in a sleep-like state but has no brain. Jellyfish also appear to sleep and they don’t have a brain either.
In a statement, Taichi Q. Itoh, who is an assistant professor at Kyushu University in Japan and an author of the study, stated, “We now have strong evidence that animals must have acquired the need to sleep before acquiring a brain,” adding, “Based on our findings and previous reports regarding jellyfish, we can say that sleep evolution is independent of brain evolution.”
For their study, the researchers used a video-recording system to watch the hydras in order to find out whether or not they actually slept or if they just remained motionless which could be disrupted by flashing a light on them. During their experiment they realized that the creatures had about four hours each of active and sleep states.
And when their sleep state was disrupted, the creatures showed signs of sleep deprivation and that they needed extra “shut-eye” as well as showing signs of decreased cell growth. Additionally, when the hydras’ sleep was disrupted and they were tired, the expression of over 200 of their genes had all changed.
Another interesting experiment was when the hydras were given chemicals like melatonin and the neurotransmitter that helps to regulate sleep in humans, the creatures’ sleep activity actually increased. When the hydras were given dopamine, it made them sleep more as Itoh explained that “while some sleep mechanisms appear to have been conserved, others may have switched function during evolution of the brain.”
In closing, Itoh said that “these experiments provide strong evidence that animals acquired sleep-related mechanisms before the evolutional development of the central nervous system and that many of these mechanisms were conserved as brains evolved.”
We all need sleep (both animals and humans) but it was previously unknown whether sleep evolved prior to that of brains but this new study seems to confirm that. Well, at least now we know that those people who we question whether or not their brains are really working can still get a good night sleep.
The study was published in the journal Science Advances where it can be read in full.