Information transfer efficiency differs in wild chimpanzees and bonobos, but not social-cognition

Several theories have been generated to understand the socio-cognitive mechanisms underlying the unique cooperative abilities of humans. The “interdependence hypothesis” posits that the cognitive dimension of human cooperation evolved in contexts when several individuals needed to collaborate to achieve a common goal and that more interdependent individuals are more likely to cooperate (provide services to conspecifics) in non-collaborative contexts. Alternatively, the “social tolerance hypothesis” proposes that higher social tolerance allows conspecifics to cooperate more efficiently and with a wider range of partners. We conducted the first field experimental evaluation of both hypotheses in our closest living relatives by contrasting chimpanzees to the less interdependent but more tolerant bonobos. We compared each species’ performance during a non-collaborative cooperative task: informing conspecifics about a danger. We presented Gaboon viper models to 82 individuals from 5 wild communities. Chimpanzees arriving late at the snake were significantly more likely to have heard a call and less likely to startle, indicating that chimpanzees were better informed about the presence of the threat than bonobos. This stems from clear species differences in how individuals adjusted their calling decisions to the level of information already available. Chimpanzees were more likely to call and produced more alarm calls when they had not yet heard a call, whereas bonobos did so when they already heard a call. Our results confirm the link between interdependence and cooperation performance. These species differences were most likely driven by differences in motivation rather than in cognitive capacities since both species tended to consider audience knowledge in their decision to call. Our results inform theories on the evolution of human cooperation by linking inter-group competition pressure and in-group cooperative motivation and/or capability.

学界已提出多种理论，旨在解析人类独有的合作能力背后的社会认知机制。依存性假说（interdependence hypothesis）指出，人类合作的认知维度演化于多个个体需协同达成共同目标的场景中，且依存性更强的个体在非协作场景下更倾向于与同种个体开展合作（即为同种个体提供服务）。与之相对的社会容忍度假说（social tolerance hypothesis）则提出，更高的社会容忍度可使同种个体间的合作更为高效，且合作伙伴的选择范围更广。我们以现存与人类亲缘关系最近的灵长类为研究对象，通过对比依存性较弱但社会容忍度更高的倭黑猩猩与黑猩猩，首次对这两种假说开展了野外实验评估。我们对比了两个物种在一项非协作性合作任务中的表现：即向同种个体传递危险预警。我们向来自5个野生社群的82只个体展示了加蓬蝰蛇（Gaboon viper）模型。较晚抵达加蓬蝰蛇模型附近的黑猩猩，其听到叫声的概率显著更高，而受惊的概率则显著更低，这表明黑猩猩比倭黑猩猩更清楚威胁的存在。这一差异源于两个物种在根据已有信息调整叫声发出决策方面存在显著的物种特异性差异。黑猩猩在未听到其他个体叫声时，更有可能发出叫声且产生更多的警报叫声；而倭黑猩猩则是在已听到叫声时才会做出此类行为。我们的研究结果证实了依存性与合作表现之间的关联。这类物种间的差异极有可能源于动机层面的不同，而非认知能力的差异，因为两个物种在做出叫声发出的决策时，都会考量受众的已有认知水平。我们的研究结果通过关联群体间竞争压力与群体内合作动机及（或）合作能力，为人类合作演化的相关理论提供了新的实证依据。