Sleeping in one 8-hour block at night seems to be a recent invention. http://discovermagazine.com/2007/dec/sleeping-like-a-hunter-gatherer http://discovermagaz

Sleeping in one 8-hour block at night seems to be a recent invention. http://discovermagazine.com/2007/dec/sleeping-like-a-hunter-gatherer http://discovermagazine.com/2007/dec/sleeping-like-a-hunter-... "...the Ibans of Sarawak, 25 percent of whom are apparently active at any one point in the night."