Early human sleep was shaped by survival needs. Before permanent settlements and modern comforts, sleep presented unique challenges, influencing where and how ancestors rested. Understanding these adaptations provides insight into human behavior and biology. Strategies for safe slumber intertwined with social structures and technology, highlighting the interplay of biology, environment, and culture in human evolution.
Choosing a Safe Sleeping Place
Early humans prioritized locations offering natural protection from predators and elements. Caves and rock shelters provided immediate refuge, shielding from harsh weather and offering elevated vantage points. These natural formations acted as strategic strongholds, limiting approach paths for potential threats. Archaeological evidence from South Africa’s Border Cave indicates early humans utilized these spaces, creating rudimentary bedding from grass and ash to improve comfort and deter insects.
Beyond caves, elevated ground and dense tree cover were selected for defensive advantages. Sleeping in trees, a practice observed in earlier hominids, offered protection from ground-dwelling predators. As humans transitioned to terrestrial lifestyles, they sought locations with good visibility and escape routes for early danger detection. Temporary structures from branches and animal skins could be quickly assembled where natural shelters lacked, providing basic safety and comfort.
Strategies for Protection During Sleep
Active measures also enhanced security. Communal sleeping was a prevalent strategy, with groups resting together for collective vigilance and defense. This arrangement meant that not all individuals would be deeply asleep simultaneously, increasing the likelihood of detecting threats. This social sleep hypothesis suggests that sleeping in large groups allowed for shared responsibility.
Control of fire, a significant technological advancement, provided warmth, light, and a powerful deterrent against nocturnal predators. Fire allowed human activity to extend into the darker hours, making sleeping sites less vulnerable. This innovation enabled early hominids to engage in more rapid eye movement (REM) sleep, a deeper sleep stage, improving cognitive functions like learning.
The Nature of Ancient Human Sleep
Research into modern hunter-gatherer societies like the Hadza, San, and Tsimane offers insights into ancestral sleep patterns. These groups sleep for shorter durations than often assumed, averaging 5.7 to 7.1 hours nightly. They go to sleep several hours after sunset and awaken before sunrise, challenging the notion that pre-industrial humans slept immediately after dark. This sleep duration is at the lower end of what is observed in industrialized societies, suggesting that modern life has not necessarily reduced sleep time compared to our ancestors.
Ancient human sleep was likely monophasic, a single continuous period of rest, rather than a fragmented or biphasic pattern. While some historical evidence suggests biphasic sleep (two distinct sleep periods) was common in preindustrial Europe, studies of contemporary hunter-gatherers do not support this as a universal ancestral pattern. The ability to achieve relatively deep sleep within a shorter timeframe, including a higher proportion of REM sleep compared to other primates, may have been an evolutionary adaptation. This efficient sleep allowed more time for waking activities like social learning and strengthening community ties, which were beneficial for survival. Temperature appears to be a primary regulator of their sleep-wake cycles; individuals often fell asleep as ambient temperatures dropped and woke at their lowest point.