Humans Sleep 35% Less Than Primates Should
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- Humans sleep roughly 7 hours per day — about 35% less than the 9.5 hours a primate of their body size, brain size, reproductive schedule and sleeping environment would be predicted to need, based on data from 30 primate species.
- A 2018 study with Charles Nunn at Duke University compared sleep across 30 primates including chimps, orangutans, macaques and lemurs, finding humans hold the highest proportion of REM sleep among the sampled species.
- The model predicted 8.4 hours of NREM sleep for humans, but actual time spent in this phase is 5.4 hours — meaning humans compressed their nights mainly by cutting NREM, not REM, the opposite of what most species under sleep pressure do.
- Humans are the only primates that regularly sleep on the ground across all age and sex classes, with the shift becoming a defining trait by the time of Homo erectus around 1.8 million years ago, according to the source.
- The author proposes a 'sleep exophenotype' — extending biologist Richard Dawkins' extended-phenotype concept — arguing humans built collective sleep safety through cooperation, fire, shelter and shared vigilance.
- The findings are drawn from 'The Sleepless Ape,' a new book that frames human sleep as an evolutionary outlier rather than a product of modern stress, with field research conducted in chimpanzee nests 12 metres above Uganda's Toro-Semliki Wildlife Reserve.
Why it matters: The comparative primate record suggests humans were already short sleepers before electricity, alarm clocks or screens — a finding that complicates the popular 'paleo sleep' movement and undermines the idea that the 7-hour average is a modern aberration. The author ties the shift to Homo erectus roughly 1.8 million years ago, implying our short-sleep architecture predates urban life by orders of magnitude.
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