No brain? No problem. Humans and jellyfish sleep in a similar way

What do jellyfish and people have in common?

Well a new study from scientists at Bar-Ilan University suggests despite lacking a brain, jellyfish and sea anemones sleep similarly to humans.

Researchers say they sleep for around eight hours a day and take midday naps.

It's thought that by studying ancient sea animals like these, it can help scientists understand how sleep originated and evolved.

For animals with a brain, sleep is really important for storing memories, restoring energy, helping the immune system and giving the body a chance to repair itself.

Unlike humans, animals in the wild don't get to snuggle up in a warm cosy bed and feel safe at night.

In fact, sleeping leaves them vulnerable to predators and other hazards in the environment.

Because of this, most scientists say sleep must be a very important biological function, especially as every animal with a nervous system has been seen to exhibit the behaviour, despite years and years of evolution.

So why do animals without a brain also need to sleep?

The theory is that sleep helps to protect the DNA in nerve cells and repairs the damage done while animals are awake and animals evolved the function millions of years ago.

Nerve cells, which send signals between the body and the brain, don't divide, so any damage must be repaired for them to be able to continue to function.

In this study, researchers looked at a species of upside down jellyfish called Cassiopea andromeda.

They simulated day and night using lights and found that during daylight, the jellyfish pulsed their bodies around 37 times per minute on average, whereas at night they pulsed less often.

The scientists also looked at how they responded to sudden bright light or food, both in the daylight and night.

They took longer to respond in the dark suggesting they were asleep.

It was even found that when the jellyfish had been disturbed lots during the night, they napped more during the day.