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Free keywords:
honest signaling; smiling; experiment; trust game; video
Abstract:
We test the hypothesis that smiles perceived as honest serve as a signal that has evolved to induce
cooperation in situations requiring mutual trust. Potential trustees (84 participants from Toulouse, France)
made two video clips averaging around 15 seconds for viewing by potential senders before the latter decided
whether to ‘send’ or ‘keep’ a lower stake (4 euros) or higher stake (8 euros). Senders (198 participants from
Lyon, France) made trust decisions with respect to the recorded clips. If money was sent to the trustee, stakes
were tripled and trustees could decide to keep all, two thirds or one half of the tripled stakes. Clips were
further rated concerning the genuineness of the displayed smiles. We observe that smiles rated as more
genuine strongly predict judgments about the trustworthiness of trustees, and willingness to send them
money. We observe a relation between costs and benefits: smiles from trustees playing for higher stakes are
rated as significantly more genuine. Finally, we show that those rated as smiling genuinely return more
money on average to senders. An increase of one standard deviation in rating of smile genuineness is
associated with an unconditional expected gain of about one dollar and thirty cents to senders in the two trials
of the experiment. Potential gains for senders could be significantly increased from taking smiles rated as
genuine into account
