Abstract
The community of Pygmies settled in Vyegwa-Gika provides an exceptional case study to test the role of trust in the evolution of altruism. The Vyegwa-Gika Pygmies were forced to migrate from rainforests to the savanna, changing quickly their environment, culture, and socio-economic situation. Despite the high level of poverty they suffer in this new settlement, we found evidence of strong altruistic attitudes toward trustees when playing an economic game. In addition, Vyegwa-Gika Pygmies keep small personal trust networks despite the fact they share frequent social interactions within the community. These results indicate the great effectiveness of personal trust in fostering altruism, even if the circumstances make it difficult to establish such kind of affective bonds. A theory of the evolution of altruism should therefore also account for the evolution of psychology of trust, as a key element in the process.
Highlights
Altruism is a striking feature in humans compared to other species
A proper explanation of the evolution of altruism should consider the evolution of the psychological mechanisms that may generate such behaviors [15]
For example, it has been proposed that cooperation by reciprocity requires a psychological mechanism to estimate similar exchanges
Summary
Altruism is a striking feature in humans compared to other species. Many of the explanations of its evolution focus on altruistic behaviors toward relatives–biological altruism [1, 2, 3]; toward group members–genetic [4] and cultural [5] group selection, parochial altruism [6]; or toward any other people by reciprocal cooperation–reciprocal altruism [7, 8], altruistic rewarding [9]–or indirect reciprocity–altruistic reputation [10, 11, 12], altruistic punishment [13, 14].a proper explanation of the evolution of altruism should consider the evolution of the psychological mechanisms that may generate such behaviors [15]. For example, it has been proposed that cooperation by reciprocity requires a psychological mechanism to estimate similar exchanges. This mechanism would give rise to the selection of reciprocating partners [16]. A different approach, the one we favor, focuses on personal trust, understood as the positive expectations about known people’s behavior, as a key psychological mechanism in this regard. Personal trust makes humans develop affective bonds beyond kin, and this feeling of affiliation toward trustees promotes to behave in favor of them, to expect them to do the same for us, and so to prefer them for reciprocal exchanges [17, 18]. Previous studies have shown that personal trust can extend cooperation beyond trustees within a group, in an emotion-driven, non-strategic way, which leads to higher levels of group cooperation and cohesion
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