As we age, we get poorer and poorer sleep, but that might actually be an evolutionary adaptation that helped humans survive at night by ensuring one person in a community was awake at all times, according to a study of Hadza hunter-gatherers published this week in Proceedings of the Royal Society B. The authors call it sharing "the task of vigilance during sleep" in order to "reduce the dangers of sleep."
Why it matters: Other studies have shown an age-related variation in sleep times, but this is the first to find it in humans, Alyssa Crittenden, author of the study and an associate professor of anthropology at the University of Nevada, Las Vegas told the NYT. Plus, this could explain why human communities historically have slept in mixed-age groups. "We may be looking at just another reason why grandparents were critical in human evolution," Crittenden said.