Conservation depends upon getting the incentives right. This is not a new idea. Plato and the Bible both have it. It follows from modern economic theory. Yet the idea that self-interest motivates people to conserve, or abuse, resources gives rise to a great deal of heated controversy. Some ethical systems teach that self-interest is not a legitimate motive, presenting it instead as mean or dishonorable. 'Altruism," acting against one's own interest in order to benefit another, is held out as the ideal for ethical conduct. Exhortations to be altruistic discount human nature, that is, other players in the game are all too ready to take without giving back fair value. The argument about ethical conduct and human nature continues on many levels, and at least some of these bear on the environmentalist's incentive to conserve.