So That’s Why Some People Are Night Owls And Others Are Up At The Crack Of Dawn

Researchers tested the sentinel hypothesis in humans by looking at the sleep patterns of a rural Tanzanian tribe. Over the nearly three weeks of the study, they found that 99.8 percent of the time, at least one adult in the tribe was awake. The adults averaged just over six hours of total sleep a night and spent nearly two-and-a-half hours awake each night after initially falling asleep. In short, they had widely different sleep schedules. And whether intentionally or not, somebody was nearly always “on guard.”