Trustworthiness: an adaptationist account

Abstract

The concept of trustworthiness plays a role in the formation, maintenance, and dissolution of friendships, marriages, and cooperative relationships from small to large scales. Here, we analyze trustworthiness under the assumption that such concepts evolved to guide action adaptively. Intuition and research suggest that actors trust targets who have not engaged in betrayals. However, this perspective fails to capture certain real-world behaviors (e.g., when two people cheating on their spouses enter a relationship with each other and expect mutual fidelity). Evolutionary task analysis suggests that trustworthiness is structured to help actors address challenges of extending trust, where actors may gain or lose from doing so. In six experiments with American adults (N = 1718), we test the hypothesis that trustworthiness tracks not only (i) whether targets refrain from betraying trust when given opportunities, but also (ii) the impact of betrayal on the actor. Data generally support this hypothesis across relationships (friendships, romantic, professional): Actors deem non-betrayers more trustworthy than betrayers, but also deem betrayers more trustworthy when betrayals benefit actors. Trustworthiness may incline actors to trust to those who refrain from betraying others—a potent signal of reluctance to betray oneself—while also favoring those who betray others if it serves oneself.