All night long people are up and down, the noise complicating sleep. Parties. Barking dogs. Motorcycles and cars driving by. Kids crying. People talking, laughing, using the bathroom. Sleep becomes a thing of fragments. We all know the story, right? Downtown Manhattan? Krzyzewskiville?
Try Mandena, a town in Madagascar chosen specifically because it’s so far off the grid that with no electricity—and so no electric lights or glowing screens to wreck people’s sleep patterns—it provided a perfect location for a study of natural sleep. Evolutionary biologist David Samson is a postdoc in the lab of Charles Nunn, which investigates health from ecological and evolutionary perspectives. With support from Bass Connections and the Duke Global Health Institute, the Nunn lab was undertaking a multiyear series of studies on health in Madagascar. Samson was part of the team, “and my sliver of it was on sleep.”
Mandena, a village of between 2,000 and 4,000 people, sits in the rainforest in the shadow of the Marojejy mountain chain and provides a home for several Duke research projects. The Nunn lab is investigating how the transition from a traditional, agricultural economy to a more modern one affects health, and every year Duke groups return. “We’re immersed in this village,” Nunn has said. “Ultimately, our goal is really to improve the health of this village.”
Samson first studied sleep through climbing trees in Africa to quantify chimp sleep platforms, then expanded his interest to “sleep architecture”—REM versus non-REM sleep—when studying orangutans in the Indianapolis Zoo. Primate sleep became a focus for him, and in 2015 he and Nunn wrote a paper sharing the finding that humans sleep less, yet more deeply, than any other primate. Coming down from the trees and developing things like fire meant that we learned to sleep comfortably and deeply, which meant we could sleep better and sleep less.
Fast-forward to modern life, with electric lights and television screens, and you start wondering about that sleep, though. “Ninety-nine percent of everyone that lives in a developed economy lives in what is called a light-polluted area,” Samson says, which means the way people naturally sleep is almost impossible to find anymore. Which is how an evolutionary biologist finds himself in Mandena. Samson put wristbands with light and motion detectors on twenty- one people aged nineteen to fifty-nine (adding EKGstyle electrodes to measure sleep architecture to nine of them). And he discovered that the villagers went to bed a couple of hours after sunset and got up an hour or so before sunrise, but of the ten or so hours in between, they spent only about six and a half actually sleeping.
Which it turns out jibes with traditional descriptions of sleep. “In preindustrial Europe there was a lot of references to first sleep and second sleep,” Samson says: People would sleep a few hours, then be awake and active a while, then sleep some more. The people in Mandena actually slept less overnight than average people in the developed world, though they made up for that with naps.
Samson hopes to continue investigating. Because light and temperature are key environmental cues that guide sleep patterns, Samson says, “the next goal is to be able to get a similarly traditional population, but in high latitudes. That’s where we’re going to see human plasticity come into play and answer questions.” At high latitudes both temperature and light-dark cycles vary widely through the year. Studying people who live with those changes will help Samson toward one of his ultimate goals, a global data set on traditional sleep.