“Lizzie had once briefly toyed with the idea of studying developmental psychology—she’d never much liked children, but she did love the idea of them as natural-born physicists, the theory that babies began life as miniature Aristotelians and only by trial and error discovered Galilean inertia and Newtonian motion, every toddler a live-action Wile E. Coyote, running off the cliff and learning gravity on the way down. It occurred to her now to imagine a moral philosophy taking shape in the same way, baby Hobbeses and little Lockes bumping into sin and consequence.”