Humans have evolved to sleep for shorter periods in deeper sleep, say researchers.
The study, published in the journal Evolutionary Anthropology, examines sleep patterns across hundreds of mammals, including 21 species of primates such as baboons, lemurs, chimpanzees and humans.
According to the Centers for Disease Control and Prevention (CDC), how much sleep we need as individuals varies, but it changes as we age. For example, school-age children need about 10 hours of sleep each day, while teenagers need 9-10.
Adults need around 7-8 hours of sleep a day, but according to data from the National Health Interview Survey, almost 30% of adults sleep a reported average of less than 6 hours of sleep each night.
The researchers, led by anthropologist David Samson of Duke University in North Carolina, compiled a database of sleep patterns across mammals and then used statistical techniques to account for each species' hierarchy in the primate family tree.
Humans spend 25% of sleep in REM phase
The team found that humans are the shortest sleepers - slumbering for an average of 7 hours each night - while other species of primate, such as the southern pig-tailed macaques and gray mouse lemurs, need 14-17 hours.
- Sleep insufficiency is linked to car crashes, industrial disasters and medical or other occupational errors
- In the US, 50-70 million adults have sleep or wakefulness disorder
- On average, adults need 7-8 hours of sleep each night.
Additionally, the team found that our sleep is more efficient. We spend nearly 25% of our overall sleep in rapid eye movement (REM) sleep - which is a deeper stage of sleep - whereas other primates spend only 5% of their time in this sleep state.
Samson spent nearly 2,000 hours watching orangutans in REM and non-REM sleep as part of his dissertation research before he came to Duke. He notes that humans "are unique in having shorter, higher quality sleep."
In our modern world of artificial lights and gadgets with screens, it would be easy to blame technology for our shift in sleeping patterns, but the team says this is not the culprit.
A completely different study into sleeping habits of hunter-gatherer societies without electricity in Tanzania, Namibia and Bolivia concluded that they actually get less sleep than those of us in a tech-obsessed society.
Samson notes that if modern life were to blame for our shortened sleep, these hunter-gatherer societies that do not have access to electricity would presumably sleep more.
The 'sleep intensity hypothesis'
As a result of their findings, the researchers propose a "sleep intensity hypothesis," which suggests that early humans encountered "selective pressure" to get quality sleep in the shortest amount of time possible.
"Several factors likely served as selective pressures for more efficient sleep, including increased predation risk in terrestrial environments, threats from intergroup conflict and benefits arising from increased social interaction."
The researchers add that less sleep would give early humans longer periods of activeness, during which they could acquire new skills and knowledge. Meanwhile, deeper sleep is necessary to consolidate these skills and leads to "enhanced cognitive abilities."
Samson says the shift toward shorter, more efficient sleep likely coincided with early humans transitioning from sleeping in trees to sleeping on the ground, where they likely slept near fire and in larger groups to keep warm and ward off predators.
Medical News Today recently reported on a study that suggested the brain's ability to regulate emotions is compromised by fatigue, and sleep deprivation, therefore, affects our ability to allocate brain resources for cognitive processing.