Runaway social selection for displays of partner value and altruism

The discovery of evolutionary explanations for cooperation is one of the great achievements of late 20th century biology. As most readers know, benefits to the group rarely explain tendencies to help others (Williams, 1966; Dawkins, 1976), benefits to kin explain altruism in proportion to the coefficient of relatedness (Hamilton, 1964), and mutual benefits and reciprocal exchanges explain much cooperation between nonrelatives (Trivers, 1971). Subsequent theoretical and empirical studies have blossomed into a body of knowledge that can explain much social behavior (Wilson, 1975; Trivers, 1985; Dugatkin, 1997; Alcock, 2001; Hammerstein, 2003).