Dufour V, Pelé M, Sterck E H M, Thierry B
Ethology Research, Animal Science Department, Biomedical Primate Research Centre, Rijswijk, Netherlands.
J Comp Psychol. 2007 May;121(2):145-55. doi: 10.1037/0735-7036.121.2.145.
Despite controversial expectations that animals achieve reciprocal altruism, it is unclear if nonhuman species possess the necessary cognitive abilities. For reciprocal altruism, individuals must anticipate the loss of a commodity and accept a delay before some return. The authors investigated the abilities of 5 chimpanzees (Pan troglodytes) to cope with increasing waiting duration in exchange tasks. Subjects had to keep a small cookie before returning it to a human partner to obtain a larger piece. For a piece 2, 4, or 8 times the size of the small piece, 3 of the 5 subjects waited for up to 4 min. For a piece 40 times larger, 4 of the 5 subjects waited up to 8 min. At long time lag, renouncement to wait occurred earlier than predicted by subjects' general waiting capacity, suggesting that the decision to wait was based on a trade-off between reward quantity and expected costs of the waiting duration. Chimpanzees could anticipate a delayed reward at a time scale of several minutes. If this reflects a cognitive limit in chimpanzees' anticipation capacity, reciprocal altruism by keeping track of costs and benefits over extended periods may be unlikely in chimpanzees.
尽管对于动物能够实现互惠利他行为存在争议性的预期，但尚不清楚非人类物种是否具备必要的认知能力。对于互惠利他行为而言，个体必须预期到一种商品的损失，并接受在获得回报之前的延迟。作者研究了5只黑猩猩（Pan troglodytes）在交换任务中应对等待时间增加的能力。受试者必须先保留一块小饼干，然后将其归还给人类伙伴，以换取更大的一块。对于大小为小块饼干2倍、4倍或8倍的一块饼干，5只受试者中有3只等待了长达4分钟。对于大40倍的一块饼干，5只受试者中有4只等待了长达8分钟。在长时间间隔时，放弃等待的时间比受试者的一般等待能力所预测的要早，这表明等待的决定是基于奖励数量与等待持续时间的预期成本之间的权衡。黑猩猩能够在几分钟的时间尺度上预期延迟奖励。如果这反映了黑猩猩预期能力的认知极限，那么通过在较长时期内跟踪成本和收益来实现互惠利他行为在黑猩猩中可能不太可能。
