Humans sleep roughly six to eight hours nightly, substantially less than our closest primate relatives. Chimpanzees and gorillas sleep nine to ten hours daily, while orangutans rest even longer. Evolutionary anthropologist David Samson of the University of Toronto investigated why our species abandoned the sleep patterns of other apes, tracing the shift through our ancestral history.
Samson's research suggests that reduced sleep emerged as humans began controlling fire and organizing nighttime activities around 1.5 million years ago. Artificial light extended waking hours, allowing our ancestors to forage longer, cook food more efficiently, and maintain social bonds through evening gatherings. These nighttime advantages offset sleep's biological costs, selecting for individuals who required less rest.
The transition involved metabolic tradeoffs. Cooking made food more digestible and energy-dense, reducing the calories needed for digestion and enabling shorter sleep periods. Larger brains demand substantial energy, but more efficient fuel from cooked meals freed resources previously allocated to sleep. Group living around fires also reduced predation risk, allowing humans to sleep in shorter bursts or lighter stages rather than the deep, prolonged sleep required by solitary primates.
Samson's work reveals counterintuitive benefits of our abbreviated sleep. Wakefulness at night improved vigilance, enabled tool-making by firelight, and strengthened social hierarchies through nocturnal interaction. These cognitive and social advantages compounded across generations, favoring genetic variants supporting reduced sleep needs while maintaining cognitive function.
However, modern sleep deprivation differs dramatically from ancestral patterns. Our ancestors likely slept in segmented chunks and napped throughout the day. Contemporary schedules force consolidated nighttime sleep with constant daytime obligations, straining circadian rhythms evolved for segmented rest. Samson's research underscores why contemporary humans report sleep troubles despite genetic adaptation to shorter rest.