8-hour sleep rule dates back to the 19th century. A new review of hunter-gatherers whose lifestyles are closer to our ancestors and who have little or no access to artificial light found short nights (5.7 to 7.1 hours) seemed to be enough: without an alarm clock, they tended to wake close to dawn.

8-hour sleep rule dates back to the 19th century. A new review of hunter-gatherers whose lifestyles are closer to our ancestors and who have little or no access to artificial light found short nights (5.7 to 7.1 hours) seemed to be enough: without an alarm clock, they tended to wake close to dawn.