Humans are efficient sleepers, and that's why we need less sleep - seven hours - compared to as much as 14 hours a day for our closest animal relatives,
Researchers at Duke University compiled a database of sleep patterns of hundreds of mammals, including 21 primate species. They found that not only do humans need less sleep than chimps, macaques and lemurs, we spend a greater percentage of our slumber in the deeper, more restorative stages of sleep.
That might not seem surprising in this age of electric lights and round-the-clock activities, but co-author David Samson says this shift began long before we developed artificial lighting. He traces it back to when human ancestors left their nests in the trees for sleeping on the ground.
The need to sleep near fire and in larger groups for warmth and safety could have allowed these early humans to get the most out of their sleep in the shortest possible time. He notes that also left more time for other activities, like learning new skills.