Spending a third of our lives in a state of sleep may seem like a long time, but according to recent research, humans actually get a quick, quality dose of shut-eye compared to our primate relatives. The study, reported by Duke University’s David R. Samson and Charles Nunn, is published in Evolutionary Anthropology.
To arrive at this finding, the researchers collected data on the sleep patterns of humans, hundreds of mammals, and 21 primate species. The researchers then compared all this data and used a statistical technique to account for where each species falls on the primate family tree.
It turns out, humans sleep “the least of any primate on the planet,” said Dr. Samson to The New York Times. For example, humans sleep for seven hours a night on average, whereas gray mouse lemurs can doze for up to 14 to 17 hours.
A chimpanzee nest. Chimps sleep for around 11.5 hours. Joey Verge/Wikimedia Commons
Our sleep isn’t just shorter, either. It is also more efficient: Adults spend about 22 percent of their sleep in the rapid-eye movement (REM) stage, whereas mongoose lemurs and African green monkeys spend about five percent. This longer duration of high-quality sleep allows us to consolidate more memories and learning, likely leading to enhanced cognitive abilities.
One possible reason for our higher quality, shorter-length sleep is the transition from arboreal “beds” to sleeping on the ground, according to the researchers. When we climbed down from sleeping in the trees to snoozing on the ground near fire, our sleeping habits probably changed as well.
Samson and Nunn also dismiss the possibility of artificial light playing a key role in the different sleep patterns. This is primarily due to another study, which found that hunter-gatherer societies living without electricity in Tanzania, Namibia, and Bolivia get even less sleep than artificial light-drenched sleepers.
“Several factors likely served as selective pressures for more efficient sleep,” wrote the researchers. This includes “increased predation risk in terrestrial environments, threats from intergroup conflict, and benefits arising from increased social interaction.”
As for the mammal comparisons, small mammals tend to sleep more during the day, but in shorter bouts. Apart from size, factors such as the number of animals in a group also plays a role in sleep patterns. That is, except for humans, who once again break the pattern, sleeping for far less time than expected. However, we are not the only mammals to break the trend: A platypus spends up to half its sleep in REM – a truly superior sleeper.
The precise reasons for why these patterns exist still need further investigation. “That being said, the window of possibility to test many of the relevant hypotheses that could answer the greater questions of sleep’s role in human evolution may be coming to a close,” wrote the researchers. “Wild populations of great apes are among the most endangered in the world… Therefore, generating sleep data in an ecologically relevant context is acutely urgent.”
Needless to say, a good night's sleep is a prized feat.