We evolved to sleep better in less time

Insomnia? You may want to blame evolution as a new study has revealed that humans have evolved to get better sleep in less time.

Researchers from Duke University scoured the scientific literature and compiled a database of slumber patterns across hundreds of mammals including 21 species of primates, from baboons and lemurs to orangutans, chimpanzees and people. They then used statistical techniques to account for each species' position in the primate family tree.

They found that humans are exceptionally short sleepers, getting by on an average of seven hours of sleep a night, whereas other primate species, such as southern pig-tailed macaques and gray mouse lemurs, need as many as 14 to 17 hours.

What's more, our sleep tends to be more efficient, meaning we spend a smaller proportion of time in light stages of sleep, and more of our sleep time in deeper stages of sleep. A dream state called rapid eye movement sleep, or REM, for example, makes up nearly 25 percent of our overall sleep. But in primates such as mouse lemurs, mongoose lemurs and African green monkeys, REM sleep barely climbs above five percent.

Humans are unique in having shorter, higher quality sleep, said anthropologist and study co-author David Samson.

The human sleep gap isn't merely the result of round-the-clock access to artificial light from streetlamps and computer screens, the researchers say. A separate study of the sleep habits of people living in three hunter-gatherer societies without electricity in Tanzania, Namibia and Bolivia found they get slightly less shut-eye than those of us with electronic gadgets.

The study is published in Evolutionary Anthropology.