A new study titled “Sleep Intensity and the Evolution of Human Cognition” published in the journal Evolutionary Anthropology by Duke University researchers has established that humans sleep for an average of 7 hours per night, while chimpanzees among others sleep for 14 hours per night – the result of human evolution from tree-sleepers to ground-sleepers.
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In studying sleep patterns in mammals and 21 primate species including baboons, lemurs, orangutans, chimpanzees, pig-tailed macaques, African green monkeys, and humans, the researchers found that humans are the shortest but most efficient sleepers, while other listed mammals sleep for longer hours that are not deep enough.
“Humans are unique in having shorter, higher quality sleep,” noted David Samson, an anthropologist who spent about 2,000 hours watching orangutans and others sleep in the night and day. This study was part of his dissertation research before he came to Duke University.
It could be imagined that lighted computer screens and streetlamps among other artificial light sources are responsible for people sleeping for shorter periods of time, but the researchers find this is not necessarily so.
Groups of people in rural areas without electricity in Namibia, Bolivia, and Tanzania were studied and also found to sleep for very short periods of time – averaging 7 hours even without any smartphone screen to influence their sleep.
Anthropologist Charlie Nunn of Duke and David Samson think sleeping for shorter periods of time is evolutionary in humans whose ancestors probably slept in tree-beds of twigs and leaves.
The researchers think our ancestors sleep longer in trees because they were much safer from predators and wild animals, but when they transitioned to sleeping in groups round a fire on the ground, they slept less because of the need to watch out for hyenas and leopards among others.
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Scientists say there are benefits to sleeping for shorter periods of time, and soundly too. Shorter sleep means people could have more time to developing new skills and forming social relationships, while deeper sleep increases sharper memory and boosts brainpower.