The theory goes that although we sleep for fewer hours than other primates, the sleep that we have is of high quality so we do not need as much.
To understand whether human sleep is unique, Samson and Nunn compared the sleep patterns of 21 primates, whose slumber patterns had already been analysed.
Humans therefore have the deepest sleep of any primate
As well as noting how long the animals slept for, they looked at how much time they spent in rapid-eye movement (REM) sleep. This is when we dream, and when our brain consolidates our memories into long-term storage.
Humans slept the least. The sleepiest primates were grey mouse lemurs and night monkeys, which slept for 15 and 17 hours respectively.
But in contrast, humans spent the highest proportion of their sleep in an REM state: almost 25%. “Humans therefore have the deepest sleep of any primate,” says Samson.
Other primates get much less REM sleep, between 5-10%.
Various factors are cited, like not sleeping in trees.
Regardless of why it happened, the fact remains that human sleep is strange compared to our closest living relatives. This suggests that we have evolved to need less of it.More.
Of course, spending more time in the type of slep that consolidates memories may well relate to a lifestyle that requires more learning.
See also: Human evolution, the skinny
Human origins: The war of trivial explanations
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Here’s the abstract:
Over the past four decades, scientists have made substantial progress in understanding the evolution of sleep patterns across the Tree of Life.[1, 2] Remarkably, the specifics of sleep along the human lineage have been slow to emerge. This is surprising, given our unique mental and behavioral capacity and the importance of sleep for individual cognitive performance.[3-5] One view is that our species’ sleep architecture is in accord with patterns documented in other mammals. We promote an alternative view, that human sleep is highly derived relative to that of other primates. Based on new and existing evidence, we specifically propose that humans are more efficient in their sleep patterns than are other primates, and that human sleep is shorter, deeper, and exhibits a higher proportion of REM than expected. Thus, we propose the sleep intensity hypothesis: Early humans experienced selective pressure to fulfill sleep needs in the shortest 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. Less sleep would enable longer active periods in which to acquire and transmit new skills and knowledge, while deeper sleep may be critical for the consolidation of those skills, leading to enhanced cognitive abilities in early humans. (Public access) – Sleep intensity and the evolution of human cognition David R. Samson1,* andCharles L. Nunn2
Article first published online: 12 DEC 2015 DOI: 10.1002/evan.21464