Anahad O’Connor, writing for the New York Times:
But Dr. Siegel and his colleagues found no evidence of this. The hunter-gatherer groups they studied, which slept outside or in crude huts, did not go to sleep when the sun went down. Usually they stayed awake three to four hours past sunset, with no light exposure other than the faint glow of a small fire that would keep animals away and provide a bit of warmth in the winter. Most days they would wake up about an hour before sunrise.
In a typical night, they slept just six and a half hours — slightly less than the average American. In the United States, most adults sleep seven hours or more a night, though a significant portion of the population sleeps less.
Interesting study.