Sleep Talking: On the Origin of Human Language

By 1.9 Ma, our ancestors were fully terrestrial. The predator guild of Pleistocene Africa was richer than any modern equivalent, and early humans were among its prey. No other African terrestrial prey animal of hominin size can stay asleep for long without a refuge. Our ancestors had lost the safety of the trees, but they had inherited the consolidated sleep of primates. In this paper, I ask how early humans survived the night on the ground, consider five possibilities, and find that only a sleepless sentinel could have kept the others alive. But one sentinel, or even two, would have been falling asleep on their feet within weeks. What sustained the watch across months and years was the nightly appointment of a rested individual, spoken aloud before the group. I propose that this is the origin of spoken language.