Unbound: How Eight Technologies Made Us Human and Brought Our World to the Brink

by Richard L. Currier

When the emerging humans began to use fire to ward off predators after sunset, they created an artificial source of light that had the effect of suppressing the production of melatonin and delaying the onset of sleep. As a result, the adoption of fire freed the hominids from the ancient limitations of the twelve-hour tropical day and extended their normal waking hours well into the night. This is the point in human evolution when our ancestors began staying up late—extending the time of wakefulness well beyond the average period of daylight that governs the circadian rhythms of all other tropical animals. Staying up late gave the emerging humans unique new advantages. It provided additional time for eating, for making things, and for social life and communication. The human predilection to eat after the hours of darkness, to work on weaving, tool-making, and other tasks by the firelight, and to gossip, relate the events of the day, and recite folk tales and myths, represented unique behaviors that no other species could duplicate. All of these behaviors were made possible when the emerging humans first began building fires at night and staying up late, while lesser creatures slept or kept their distance.