AILSA CHANG, HOST:
A good night's sleep - we all yearn for it, we all need it, and yet there is still so much we don't know about the science of sleep or its origins. NPR's Nate Rott reports that a new study of spiders might help shed some light.
NATE ROTT, BYLINE: A few years ago, during the pandemic and office closures, Daniela Roessler, like so many of us, started working from home.
DANIELA ROESSLER: And so I was collecting spiders in the field, bringing them home and doing experiments in my living room.
ROTT: Totally normal because Roessler is an ecologist at the University of Bonn. And one night, after a day of collecting jumping spiders, she put some in boxes on her windowsill and went out to dinner with some friends.
ROESSLER: Came back home at 11 and, just out of curiosity, looked into the boxes, and they were all hanging from the top of the boxes on a silk thread.
ROTT: Appearing to be asleep.
ROESSLER: And I had never seen this before, and it was blowing my mind that this was not documented.
ROTT: Roessler says it was incredibly exciting.
ROESSLER: But the question that remained was, are they really sleeping?
ROTT: Because it turns out, to say scientifically that an animal is actually sleeping, especially an animal with no eyelids, like a spider, you really need to prove it.
ROESSLER: Basically, there's, like, five big criteria. One is a characteristic posture.
ROTT: A preferred position, like a preference to sleep on your stomach.
ROESSLER: That was ticked off just by the suspension.
ROTT: The animal also has to be inactive or dormant for a while.
ROESSLER: Which was also ticked off because they stayed in this position the whole night.
ROTT: Then they have to show the three hallmarks of sleep as we know it.
ROESSLER: One being an increased arousal threshold, meaning that you respond slower or not at all to an external stimulus.
ROTT: Been there most mornings.
ROESSLER: And the other one is homeostatic regulation.
ROTT: A need to catch up on sleep after a night without it. And finally, they had to prove the animals would wake up when disturbed. That was part of behavioral ecologist Nadja Geiger's job.
NADJA GEIGER: So I would basically wait and watch the spider until she fell asleep, and we used a very tiny mini-Bluetooth speaker, and then I would play this horrible sound...
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GEIGER: ...And record how long it takes that she actually responds to it.
ROTT: In their new study published in the Proceedings of the National Academy of Sciences, Geiger and Roessler show that jumping spiders check all of the boxes for sleep. And what's more, they also show signs of entering a rapid eye movement, or REM-like sleep cycle.
ROESSLER: We see retinal movements, twitching of the legs, very similar to a dog or a cat when it's in REM sleep and it looks like they're running.
ROTT: Scientists have also recently observed this in octopi, suggesting that similar sleep patterns may be widespread in the animal kingdom, which gets at a really big question that scientists have had for a long time. Where did sleep come from? Why did evolution decide it's OK for an animal to shut down, making itself vulnerable for a time?
AMITA SEHGAL: This is a very fundamental question, is how did sleep evolve?
ROTT: Amita Sehgal is a neuroscientist at the University of Pennsylvania. She wasn't involved in this new study, though she did help create that checklist we just went through more than 20 years ago to prove that flies sleep. And it was around that time, she says, that she had an interesting meeting. It involved the U.S. Army. And they were looking for a solution for sleep-deprived soldiers. So they asked...
SEHGAL: Can we give them a pill that will make up for the loss of sleep? And the answer was no, because we don't know why we sleep.
ROTT: We know it's restorative, but we don't really know how on a biological level. Sehgal says the answers may be found by studying sleep in animals - in zebrafish, in worms...
SEHGAL: In jellyfish, in hydra and now the jumping spider.
ROTT: Because the same type of behavior being so widespread in the animal kingdom suggests to her that sleep...
SEHGAL: Evolved much earlier in evolution than people thought.
ROTT: Perhaps in a common ancestor between humans and spiders hundreds of millions of years ago. Nate Rott, NPR News.
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UNIDENTIFIED MUSICAL ARTIST: (Singing) Didn't know what to say to bring you back to me. Feels like we've gone away. Transcript provided by NPR, Copyright NPR.
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