The value of a smile: Game theory with a human face

Many economists and biologists view cooperation as anomalous: animals (incl uding humans) that pursue their own self-interest have superior survival od ds to their altruistic or cooperative neighbors. However, in many situation s there are substantial gains to the group that can achieve cooperation amo ng its members, and to individuals who are members of those groups. For an individual, the key to successful cooperation is the ability to identify co operative partners. The ability to signal and detect the intention to coope rate would be a very valuable skill for humans to posses. Smiling is frequently observed in social interactions between humans, and m ay be used as a signal of the intention to cooperate. However, given that h umans have the ability to smile falsely, the ability to detect intentions m ay go far beyond the ability to recognize a smile. In the present study, we examine the value of a smile in a simple bargaining context. 120 subjects participate in a laboratory experiment consisting of a simple two-person, o ne-shot "trust" game with monetary payoffs. Each subject is shown a photogr aph of his partner prior to the game; the photograph is taken from a collec tion that includes one smiling and one non-smiling image for each of 60 ind ividuals. These photographs are also rated by a separate set of subjects wh o complete a semantic differential survey on affective and behavioral inter pretations of the images. Results lend some support to the prediction that smiles can elicit cooperat ion among strangers in a one-shot interaction. Other characteristics of fac es also appear to elicit cooperation. Factor analysis of the survey data re veals an important factor, termed "cooperation", which is strongly related to trusting behavior in the game. This factor is correlated with smiling, b ut is somewhat more strongly predictive of behavior than a smile alone. In addition, males are found to be more cooperative, especially towards female images, whereas females are least cooperative towards female images. (C) 2 001 Published by Elsevier Science B.V.