Why do we volunteer time? Why do we contribute money? Why, even, do we vote, if the effect of a single vote is negligible? Rationality-based microeconomic models are hard-pressed to explain such social behavior, but Howard Margolis proposes a solution. He suggests that within each person there are two selves, one selfish and the other group-oriented, and that the individual follows a Darwinian rule for allocating resources between those two selves. "Howard Margolis's intriguing ideas . . . provide an alternative to the crude models of rational choice that have dominated economics and political science for too long."-Times Literary Supplement