Are there nonverbal cues to commitment? An exploratory study using the zero-acquaintance video presentation paradigm

From the book : Evolutionary Psychology 1: 42-69.
Altruism is difficult to explain evolutionarily if subtle cheaters exist in a population (Trivers, 1971).
 A pathway to the evolutionary maintenance of cooperation is nonverbal altruist-detection.
 One adaptive advantage of nonverbal altruist-detection is the formation of trustworthy division of labour partnerships (Frank, 1988).
 Three studies were designed to test a fundamental assumption behind altruistic partner preference models.
In the first experiment perceivers (blind with respect to target altruism level) made assessments of video-clips depicting self-reported altruists and self-reported non-altruists.
 Video-clips were designed with attempts to control for attractiveness, expressiveness, role-playing ability, and verbal content.
 Overall perceivers rated altruists as more “helpful” than non-altruists.
In a second experiment manipulating the payoffs for cooperation, perceivers (blind with respect to payoff condition and altruism level) assessed altruists who were  helping others as more  “concerned” and “attentive” than non-altruists.
 However perceivers assessed the same altruists as less “concerned” and “attentive” than non-altruists when the payoffs were for self.
 This finding suggests that perceivers are sensitive to nonverbal indicators of selfishness.
 Indeed the self-reported non-altruists were more likely than selfreported altruists to retain resources for  themselves in an objective measure of cooperative tendencies (i.e.
 a dictator game).
In a third study altruists and nonaltruists’ facial expressions were analyzed.
The smile emerged as a consistent cue to altruism.
 In addition, altruists exhibited more expressions that are under involuntary control (e.g.,  orbicularis oculi) compared to non-altruists.
Findings suggest that likelihood to cooperate is signaled nonverbally and the putative cues may be under involuntary control as predicted by Frank (1988).