“Convinced that mankind had been on a journey of unrelenting progress since we emerged from the swamp, he believed the 15-hour week to be the culmination of hundreds of generations’ collective ingenuity and effort. Perhaps Keynes would have had a different view had he known that the 15-hour week was a reality for some of the handful of remaining tribes of autonomous hunter-gatherers, and that, in all probability, it was the norm for much of the history of modern Homo sapiens.”