Abstract
Sympathy and other moral emotions described by David Hume (1740/1978) and Adam Smith (1759/1966) motivate people to incur a host of costs they could easily avoid. Such emotions pose a challenge to evolutionary biologists, who have long stressed the primacy of narrow self-interest in Darwinian selection. In earlier work, I argued (Frank, 1987, 1988) that natural selection might have favored moral sentiments because of their capacity to facilitate solutions to one-shot social dilemmas. Here, I present a capsule summary of the basic argument