Data from: Marmoset monkeys evaluate third-party reciprocity

Many non-human primates have been observed to reciprocate and to understand reciprocity in one-to-one social exchanges. A recent study demonstrated that capuchin monkeys are sensitive to both third-party reciprocity and violation of reciprocity; however, whether this sensitivity is a function of general intelligence, evidenced by their larger brain size relative to other primates, remains unclear. We hypothesized that highly pro-social primates, even with a relatively smaller brain, would be sensitive to others' reciprocity. Here, we show that common marmosets discriminated between human actors who reciprocated in social exchanges with others and those who did not. Monkeys accepted rewards less frequently from non-reciprocators than they did from reciprocators when the non-reciprocators had retained all food items, but they accepted rewards from both actors equally when they had observed reciprocal exchange between the actors. These results suggest that mechanisms to detect unfair reciprocity in third-party social exchanges do not require domain-general higher cognitive ability based on proportionally larger brains, but rather emerge from the cooperative and pro-social tendencies of species, and thereby suggest this ability evolved in multiple primate lineages.已有研究观测到，诸多非人灵长类动物可在一对一的社会互动中实施互惠行为，并理解互惠规则。近期一项研究表明，卷尾猴（capuchin monkeys）对第三方互惠（third-party reciprocity）及互惠违规均具备敏感性，但该敏感性是否由相较于其他灵长类更大的脑容量所体现的一般智力所介导，目前仍无定论。我们提出研究假设：即便脑容量相对较小的高度亲社会灵长类动物，也能够感知他人的互惠行为。本研究结果显示，普通狨猴（common marmosets）能够区分在社会互动中与他人实施互惠行为的人类行为者，与未实施互惠行为的人类行为者：当未实施互惠的行为者留存了全部食物时，狨猴从这类非互惠者处获取奖励的频率，显著低于从互惠者处获取奖励的频率；但当狨猴观察到行为者之间存在互惠互动时，二者获取奖励的频率并无显著差异。上述结果表明，用于检测第三方社会互动中不公平互惠行为的认知机制，并不依赖于以相对更大脑容量为基础的领域一般性高级认知能力，而是源于物种自身的合作与亲社会倾向；这一发现提示该能力在多个灵长类谱系中独立演化而来。