Runaway Social Selection for Displays of Partner Value and Altruism

Randolph M. Nesse Departments of Psychiatry, Psychology, and Research Center for Group Dynamics at the Institute for Social Research University of Michigan Ann Arbor, MI, USA [email protected] Abstract Runaway social selection resulting from partner choice may have shaped aspects of human cooperation and complex sociality that are otherwise hard to account for. Social selection is the subtype of natural selection that results from the social behaviors of other individuals. Competition to be chosen as a social partner can, like competition to be chosen as a mate, result in runaway selection that shapes extreme traits. People prefer partners who display valuable resources and bestow them selectively on close partners. The resulting phenotypic covariance between displays and preferences gives fitness advantages to both, creating runaway selection that could shape a whole suite of prosocial traits including altruism, moral capacities, empathy, and theory of mind. Even though they give a net fitness benefit, traits at the endpoint of runaway social selection can have substantial deleterious effects on other traits such as viability, ability to accumulate resources, or vulnerability to mental disorders. Social selection forces arising from self-interested partner choices may be an invisible hand that shaped capacities for commitment, altruism, and other prosocial capacities of the human social brain.