Unconditional altruism is an enduring puzzle for evolutionary approaches to social behavior. In this paper we argue that costly signaling theory, a well-established framework in biology and economics, may be useful to shed light on the individual differences in human unconditional altruism....

We present the referral-backfire effect, reflecting the phenomenon that consumers become less susceptible to persuasive attempts when they experienced referral failure. In two lab studies and one field study, we provide evidence for the effect and for the hypothesis that the effect occurs...