Anthropological Institute and Museum, University of Zurich, Zurich, Switzerland.
PLoS One. 2013 Jul 3;8(7):e68440. doi: 10.1371/journal.pone.0068440. Print 2013.
Various nonhuman primate species have been tested with prosocial games (i.e. derivates from dictator games) in order to better understand the evolutionary origin of proactive prosociality in humans. Results of these efforts are mixed, and it is difficult to disentangle true species differences from methodological artifacts. We tested 2- to 5-year-old children with a costly and a cost-free version of a prosocial game that differ with regard to the payoff distribution and are widely used with nonhuman primates. Simultaneously, we assessed the subjects' level of Theory of Mind understanding. Prosocial behavior was demonstrated with the prosocial game, and did not increase with more advanced Theory of Mind understanding. However, prosocial behavior could only be detected with the costly version of the game, whereas the children failed the cost-free version that is most commonly used with nonhuman primates. A detailed comparison of the children's behavior in the two versions of the game indicates that the failure was due to higher attentional demands of the cost-free version, rather than to a lack of prosociality per se. Our results thus show (i) that subtle differences in prosociality tasks can substantially bias the outcome and thus prevent meaningful species comparisons, and (ii) that like in nonhuman primates, prosocial behavior in human children does not require advanced Theory of Mind understanding in the present context. However, both developmental and comparative psychology accumulate increasing evidence for the multidimensionality of prosocial behaviors, suggesting that different forms of prosociality are also regulated differentially. For future efforts to understand the evolutionary origin of prosociality it is thus crucial to take this heterogeneity into account.
各种非人类灵长类动物已经通过亲社会游戏（即源自独裁者游戏的衍生物）进行了测试，以便更好地理解人类主动亲社会行为的进化起源。这些努力的结果喜忧参半，很难将真正的物种差异与方法学上的差异区分开来。我们用一种有代价和无代价的亲社会游戏测试了 2 至 5 岁的儿童，这两种游戏在收益分配上有所不同，并且广泛用于非人类灵长类动物。同时，我们评估了受试者的心理理论理解水平。亲社会行为是通过亲社会游戏表现出来的，而且不会随着心理理论理解的提高而增加。然而，只有在代价高昂的游戏版本中才能检测到亲社会行为，而儿童在非人类灵长类动物最常用的无代价版本中失败了。对儿童在两种游戏版本中的行为的详细比较表明，失败是由于无代价版本的注意力要求更高，而不是由于缺乏亲社会性本身。因此，我们的结果表明（i）亲社会行为任务中的细微差异会极大地影响结果，从而阻止有意义的物种比较，以及（ii）与非人类灵长类动物一样，在当前背景下，人类儿童的亲社会行为并不需要先进的心理理论理解。然而，发展心理学和比较心理学都积累了越来越多的证据表明，亲社会行为是多维度的，这表明不同形式的亲社会行为也受到不同的调节。因此，对于未来理解亲社会行为的进化起源的努力，将这种异质性考虑进去至关重要。
