Department of Comparative Cultural Psychology, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany.
Department of Cognitive Science, University of California San Diego, San Diego, CA, USA.
Proc Biol Sci. 2021 Nov 10;288(1962):20211937. doi: 10.1098/rspb.2021.1937. Epub 2021 Nov 3.
The ultimatum game (UG) is widely used to investigate our sense of fairness, a key characteristic that differentiates us from our closest living relatives, bonobos and chimpanzees. Previous studies found that, in general, great apes behave as rational maximizers in the UG. Proposers tend to choose self-maximizing offers, while responders accept most non-zero offers. These studies do not rule out the possibility that apes can behave prosocially to improve the returns for themselves and others. However, this has never been well studied. In this study, we offer chimpanzee and bonobo proposers the possibility of taking into account the leverage of responders over the offers they receive. This leverage takes the form of access to alternatives for responders. We find that proposers tend to propose fairer offers when responders have the option to access alternatives. Furthermore, we find that both species use their leverage to reject unequal offers. Our results suggest that great apes mostly act as rational maximizers in an UG, yet access to alternatives can lead them to change their strategies such as not choosing the self-maximizing offer as proposers and not accepting every offer higher than zero as responders.
最后通牒博弈（UG）被广泛用于研究我们的公平感，这是将我们与最亲近的亲属——黑猩猩和倭黑猩猩区分开来的关键特征。先前的研究发现，一般来说，类人猿在 UG 中表现为理性最大化者。提议者倾向于选择对自己最有利的报价，而响应者则接受大多数非零报价。这些研究并未排除类人猿可能表现出亲社会行为以提高自己和他人回报的可能性。然而，这一点从未得到很好的研究。在这项研究中，我们让黑猩猩和倭黑猩猩的提议者有机会考虑到响应者对他们收到的报价的影响力。这种影响力表现为响应者获得替代方案的机会。我们发现，当响应者有选择替代方案的机会时，提议者往往会提出更公平的报价。此外，我们发现这两个物种都利用自己的影响力来拒绝不平等的报价。我们的研究结果表明，类人猿在 UG 中大多表现为理性最大化者，但获得替代方案的机会可能会促使他们改变策略，例如提议者不选择对自己最有利的报价，而响应者不接受任何高于零的报价。
