糖心原创

Do men have green beards?

Abstract: Green beards are a metaphor for any conspicuous trait that is strongly associated with an unobservable preference to behave prosocially. If such a trait exists, individuals bearing the trait will behave prosocially. If they also interact with others having the same trait, they can exclude less prosocial individuals from their social interactions. This will allow them to enjoy the benefits of mutually prosocial behavior without the costs of being exploited by defectors. The problem, however, is that known evolutionary mechanisms cannot plausibly produce and maintain the required association between the observable trait and the unobservable preference for prosocial behavior. Nonetheless, recent research has intriguingly suggested that facial width might serve as a green beard in human males, with narrow faces indi- cating prosocial tendencies. We tested this idea with a study involving two parts. In the first part, male subjects in one city played a two-person social dilemma game with no deception and real monetary stakes. In the second part, male and female raters in a different city viewed photographs of participants from the first part of the study and had to guess the behaviors of the people shown in the photographs. Raters received more money on average for accurate guesses than for inaccurate guesses. We found no evidence for facial width as a green beard. Measures of facial width from the first part of the study did not correlate with prosocial behavior, nor did they correlate with perceptions of prosocial behavior from the second part of the study. In addition, raters in the second part of the study could not predict actual cooperative behavior after viewing photographs of men’s faces. This result shows, in contrast to recent findings, that neither facial width nor any other observable trait was functioning as a green beard.