A sleep study of three primitive tribes found that these groups slept between 5.7 and 7.1 hours at night, which is shorter than what many modern people consider the “ideal 8 hours”.
The study showed that on average, they went to sleep three hours after sunset and woke up before sunrise. The sleep period coincided with the drop in temperature at night, and waking up occurred near the lowest point of the temperature. This means that temperature change is more likely than light to be the natural regulator of sleep in primitive humans.
