Public goods, sharing genes, and the formation of large groups.

Humans exhibit intense attachments to very large groups, sometimes numbering in the millions. The author addresses the question of how inclinations to attach to large groups might have evolved and identifies the problem of collective action and free riding as the central obstacles to overcome. He argues that the nonsubtractibility feature of public goods and the inclusive fitness theory of W. D. Hamilton are key elements in the evolution of sharing behavior in large groups: a source of group attachments. The argument implies that the mix of goods available and produced in past and present environments impacts the configuration of different-sized groups found in human society.