The modern welfare state is a remarkable human achievement. In Europe and North America, a substantial fraction of total income is regularly transferred from the better-off to the less well-off, and the governments that preside over these transfers are regularly endorsed by publics (Atkinson 1999). The modern welfare state is thus the most significant case in human history of a voluntary egalitarian redistribution of income among total strangers. What accounts for its popular support?

A compelling case can be made that people support the welfare state because they think it is the right thing to do. It conforms to a behavioral schema which we call strong reciprocity. Strong reciprocity is a propensity to co-operate and share with others similarly disposed, even at personal cost, and a willingness to punish those who violate co-operative and other social norms, even when punishing is personally costly and cannot be expected to result in net personal gains in the future. Strong reciprocity goes beyond self-interested forms of co-operation, which include acting tit-for-tat and what biologists call reciprocal altruism (Trivers 1971), which is really just self-interest with a long time horizon. Genuine altruism, in the standard biological sense of the term, is what motivates actors to help others in situations where the actor would increase her payoffs by not helping (Kerr, Godfrey-Smith, and Feldman 2004).