Fifty thousand years ago, a woman stands and stretches her arms, looking over America’s open plains. In the distance, she sees thirty very hairy and practically naked people speaking a language that will never be heard on the planet again. She runs, careful not to jostle the baby in her arms, joining them at the crest of a small hill. She and the other mothers, who have survived predation and the dangers of pregnancy during this hostile era, work together, stopping occasionally to nurse their children. The milk produced with the help of her community’s collective labors offers her baby the promise of another day.