Sleep has many benefits. Why do humans as a species get so little?

Experts advise that adults should sleep for around eight uninterrupted hours in a cool, dark room. If you do so consistently, they say, you can add years to your life.

It’s an ideal many people fail to live up to. It’s also, according to “The Sleepless Ape: The Story of Sleep in Human Evolution,” which published May 19, not how humans have slept for most of our evolutionary history.

Anthropologist David Samson, the book’s author and an associate professor at the University of Toronto, has scaled trees to study chimpanzee beds and visited remote tribes to understand how the story of human sleep unfolded.

Samson’s findings reveal how human sleep patterns became shorter, deeper and more flexible than those of our more ape-like ancestors, freeing time to spend on toolmaking, social interactions and migration around the world.

He argues that these unique sleep habits fostered survival, innovation and shaped our species’ behavior in pivotal ways. Today’s sleep-deprived humans can also learn a great deal from how our ancestors used to sleep, he adds.

“Sleep governs so much of our mental and physical performance throughout the day,” he told CNN. “How is it then that we are the shortest sleeping primate on the planet?”

This interview has been edited for length and clarity.

CNN: Your book is called “The Sleepless Ape.” Why’s that?

David Samson: It took about 15 years to get the prerequisite number of primate sleep studies to be able to actually run these stats, and it turns out these models were predicting that humans should sleep 10 ½ hours. I don’t know about you, but I certainly don’t sleep 10 ½ hours. The human average across cultures is probably something like seven hours. The model was predicting that we sleep much longer, which means that humans are an evolutionary outlier.

Humans are not only the shortest sleeping primate, but we also get the greatest proportion of REM sleep of any primate on the planet. And what “The Sleepless Ape” tries to explore and disentangle is the story of how that came to be.

CNN: Your book details how our ancestral species left the safety of sleeping in trees for the dangerous ground as a result of shelter, fire and social sleeping. How did that shift benefit us?

Samson: What we created was a completely new innovative space for sleep, and the analogy I’ve been using here is a shell.

We do know that early humans like Homo erectus were sleeping in groups. We can tell that right around this time there was likely the controlled use of fire. And because of the fact that you have a much larger group with demographic variability — you’ve got some grandparents in the group, you got some teens in the group —you likely had a situation where someone was awake 24/7 to sound the alarm in case of danger. It’s very clear to me that a hunter-gatherer camp would have been adapted to have larks and owls relatively distributed, such that the shell is a little bit more safe during a 24-hour period.

Many of your readers may think: “For me to get the perfect amount of sleep, I need isolation from people, I need isolation from stimulus.” But almost all the small-scale environments that I’ve ever done research in are highly dynamic environments. There is this pervasive sense of safety once you come back into the camp. It’s this little bubble, it’s this shell: “I can finally let my guard down.”

CNN: Humans have more REM sleep than other primates despite sleeping less in total. Why’s that?

Samson: When you’re in phasic REM, you’re as dead to the world as you’ll ever be. For our ancient ancestors, it was extremely costly to be in this state, but if you’ve built the shell, all of a sudden you have a new opportunity to get this really valuable sleep at higher proportions than other animals.

REM is the sleep stage famously associated with dreaming.
It’s associated with creativity and innovation, all the things that would have been, I think, prerequisite for us becoming a successful species.

CNN: Why did you study chimpanzee beds?

Samson: I’ve climbed a lot of trees. Great apes are very unique, and they build these nests that are basically tree beds. It’s fascinating. These nests keep them warm. Because they’re not on the ground, they’re solving for big predators. And because they’re made using plants that actually repelled insects, they’re also solving for micro predators.

Being able to measure their beds in situ allowed me to peek into the mind of a chimpanzee. And those are all the things that our human ancestors had to solve when we began to sleep on the ground and lost that unique sleep site.

CNN: You’ve spent time with one of the last remaining hunter-gatherer tribes on Earth, the Hadza in northern Tanzania. What did they teach you about sleep?

Samson: I think we in the West, in a way, have been fetishizing sleep as a culture. When you ask hunter-gatherers whether or not they like their sleep, they overwhelmingly say, “I love my sleep.” This is a mystery, because I know empirically they have more fragmented sleep. So, what the hell is going on? I think the resolution of this gets us to the body clock: circadian rhythms. If you look at the 24-hour period, most people spend more than 90% of their time indoors. This is abysmal.

Unless we understand how to augment and leverage the timing of our biological clocks, we’re always going to be doomed to have a weird, maybe dysfunctional or dysregulated relationship with our sleep.

CNN: How has your work on paleo sleep – sleeping like our ancestors – informed your own sleep habits?

Samson: My relationship with light has improved my sleep so much. I throw my alarms out and I let the sun do the waking. No blackout curtains or losing the cues of your outside environment. When I wake up with my morning coffee, I go outside and I share it with the sun. At noon, when you’re eating lunch, even if it’s a crappy day, it’s overcast, it’s raining, it’s cold, go out.

At night, when the sun goes down, that’s my primary cue to reduce exposure to blue light from artificial sources like screens. I might still use my phone, for example, but I’ll switch it to dark mode. And make sure that if you’re walking around your house, and I’ve been doing this for years now, it’s with little lanterns that are 2,700 kelvins and below, so it’s warm light lanterns. You just charge them in a USB port. Candlelight is even better. And also metabolic timing. My last calorie is three to four hours before my actual target bedtime.

If anybody is having trouble with their sleep, worry less about the sleep and start asking yourself, “Are you in evolutionary sync, or are you in evolutionary de-sync?” Insomnia is a great example of a classic evolutionary mismatch: the idea that we evolved for are how things were, not how things are. Insomnia is hypervigilance. Our ancestors had hypervigilance, and there was probably a very good reason why they did. They had lived in dynamic environments, and you’re the descendants of them.

I think we’re on the cusp of a sleep enlightenment in a way, because we’ve made all these gains with the comfort of our sleep site, with the safety of our sleep site, but what we’ve lost in turn is the connection with our circadian physiology. If we can marry both those things, I think we can really change our sleep and health well-being for the better in the future based on both an understanding of our evolutionary history and of modern sleep science.

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