Nighttime cooling affects sleep

It was long believed that only light regulated our biological clock. However, the coolness of the night is equally important, and our overly cozy interiors have eliminated it. Deprived of this nighttime cooling, the body struggles to find sleep.

Study on natural sleep patterns

Neuroscientists Jerome Siegel and Gandhi Yetish established in a study published in 2015 in Current Biology that the sleep of peoples living without electricity follows the drop in temperature at night more than sunset. Modern homes, which are heated and insulated, maintain the same temperature day and night, erasing this signal the body expects.

Observations of traditional communities

For retracing the sleep habits of our ancestors, anthropologist Gandhi Yetish and neurobiologist Jerome Siegel studied three populations. The Tsimane of Bolivia, the Hadza of Tanzania, and the San of southern Africa still live without electricity. Their observations revealed an unexpected phenomenon.

Sleep follows temperature changes

Contrary to common beliefs, these communities did not fall asleep immediately after nightfall. Their sleep rhythm seemed to follow the variations in external temperature. Rest generally began when the air cooled, while waking occurred during the coldest hours.

Temperature regulates the biological clock

At this moment, the body constricts its blood vessels to better retain heat. Temperature thus played a major role in their sleep, more than the simple setting of the sun. It seemed to contribute to the regulation of their biological clock.

Insomnia is not a universal concept

Another surprising feature is that some of these populations do not even have a common word to denote insomnia.