Two Victorian Era intellectual movements changed the course of American legal thought: Darwinian natural selection and marginalist economics. The two movements rested on fundamentally inconsistent premises. Darwinism emphasized instinct, random selection, and determinism; marginalism emphasized rational choice. American legal theory managed to accommodate both, although to different degrees in different disciplines. The two movements also developed mutually exclusive scientific methodologies. Darwinism emphasizing external indicators of welfare such as productivity, education or health, while...