Humans, compared to other mammals including primates, enjoy less sleep that is also more efficient, according to the findings of a new study published in the journal Evolutionary Anthropology.
A team of researchers from Duke University made a database of slumber patterns encompassing over hundreds of mammals. 21 species of primates were included in the compilation. Based on this data, they deduced the position of each species in the family tree of primates.
The results indicate that humans are, by far, short sleepers. While a mean of 7 hours of sleep per night are enough for us, other primates like the southern pig-tailed macaques and the gray mouse lemurs, have to sleep for around 14 to 17 hours. Even chimpanzees, which are considered to be our closest animal relatives, need some 11.5 hours per night.
Furthermore, the short sleep is actually more efficient because our sleep time comprises more of deep stages than light ones; for instance rapid eye movement sleep (REM) constitutes one-quarter of our sleeping time. On the other hand, less than 5 % of the sleep of primates like mouse lemurs, mongoose lemurs and African green monkeys, consists of REM. We, therefore, have a higher quality sleep, explains one of the authors, anthropologist David Samson.
Another aspect of sleep that the researchers considered entails artificial light (emanating from streetlights and our technological devices) that is said to affect human sleep; according to them, it does not completely account for our shorter sleep. Another research whose participants were hunter-gatherer societies in Tanzania, Namibia and Bolivia, who were not sustained by electricity, shows that they have even less sleep than those people living with electronic devices. This implies that access to electricity is not the only factor influencing our sleep time. Rather, it appears that we have substituted sleep quantity with sleep quality.
Why would our sleep be reduced? Perhaps, the transition from sleeping in ‘beds’ in trees to sleeping on the ground contributed to the shift, write the researchers. Sleeping on the ground would have involved certain hazards for the early humans: for instance, having fires burning nearby and larger groups in close proximity, both to keep warm and to repel predators, would have caused them to have short sleep cycles which are more efficient, according to Samson. The latter also adds that shorter sleep would make time for more activities such as social bonding, and learning of additional skills. Deep sleep would then, simultaneously, enhance memory and brainpower.