Dynamically engaged smiling predicts cooperation above and beyond average smiling levels

Abstract

Smiling has been conceptualized as a signal of cooperative intent, yet smiles are easy to fake. We suggest that contextually appropriate, dynamically engaged smiling imposes an attentional cost, thereby making engaged smiling a plausible “honest signal” of cooperative intent. To test this hypothesis, we analyzed data from 123 pairs of same-sex strangers having “getting-to-know-you” conversations who subsequently played a one-shot prisoner’s dilemma together. We calculated the strength of engagement in smiling using a cross-lagged auto-regressive model for dyadic data. We found that when an individual’s partner (the signaler) tended to smile in a more responsive way, that individual (the receiver) was more likely to cooperate. Conversely, when a signaler tended to smile in a less responsive way, the receiver was less likely to cooperate. These effects were present over- and-above the effects of average levels of smiling and self-reported liking, which also predicted likelihood of co- operation. However, dynamically engaged smiling did not predict cooperation on the part of the signaler, sug- gesting that receivers weight the importance of engagement more highly than they should, or even that engaged smiling might be a manipulative display. These results illustrate how conversational dynamics can influ- ence evolutionary signaling.