As strange as this may sound, scientists still don’t know why we sleep. Certainly there are medical benefits to rest; cells regenerate and the mind is allowed to process new information, among other things. Yet, from an evolutionary point of view, sleeping makes no sense. For one thing, it makes creatures more vulnerable to predators. For another, lacking sleep typically triggers animals to engage in risky, ill-thought behaviors. The necessity for sleep, then, has always been an enigma; one thought about but not really studied until now.

Researchers from the California Institute of Technology have discovered that even primitive jellyfish need to sleep. This may come as no surprise to some, but for evolutionary scientists, these findings are remarkable. If an animal that technically has no brain needs to sleep, the origins of rest may be more primitive than initially perceived.

Ravi Nath, the first author of the paper explains: “Everyone we talk to has an opinion about whether or not jellyfish sleep. It really forces them to grapple with the question of what sleep is.”

Do molecules sleep? Do atoms?

These are some of the more perturbing questions raised by this new analysis. Researchers in the past have thought that sleep was a complex behavior. They noted that animals from the fruit fly to the blue whale spend a large portion of their day resting. This led to the assumption that only “higher-level” organisms required sleep. This recent study, however, would suggest otherwise.

“This work provides compelling evidence for how early in evolution a sleep-like state evolved,” concluded Dion Dickman, a neuroscientist and co-author of the study.

Defining sleep

Proving that jellyfish actually sleep required defining what sleep entails. For the purposes of this study, the team came up with three criteria. These were:

1. A reduced state of activity (defined as quiescence),
2. A decreased response to stimuli (or what would otherwise be responded to if awake), and
3. An increased need to sleep if and when deprived of sleep.

The team noted that jellyfish are mostly inactive at night, only pulsing their bell around 39 times per minute instead of 58 during the day. Researchers likewise observed that jellyfish were less likely to respond to arousing stimuli during this period. This is similar to what happens to us when we sleep: Noises and sounds that we would normally react to when awake are ignored. Lastly, the researchers saw that when they deprived jellyfish of sleep, the animal was more likely to enter a quiescent state during the day.

It was concluded that jellyfish do sleep, but scientists say they still do not know why, or the genetic mechanism that governs it. Even so, they have seen that compounds such as melatonin (which influence sleep patterns) are present in predictable ways in both jellyfish and humans. This implies that there are some evolutionary bases for sleep.

The takeaway from this study

The average person doesn’t have time to dwell on whether plants or atoms sleep (if at all). What is important though is that sleep is important. It is natural and necessary for overall health. Medical doctors are now emphasizing quality over quantity when it comes to rest. The general rule of thumb is to get eight hours of sleep a day, but this varies per individual. The perfect rest is one that is uninterrupted and enough to make a person awake feeling refreshed. Feeling tired, having a headache, or needing an alarm clock to wake up are characteristic of unhealthy sleeping habits.  

Find more studies on the importance of sleep at Research.news.