The ontogeny of chimpanzee technological efficiency

Abstract

Primate extractive foraging requires years of dedicated learning. Throughout this period, learners peer at conspecifics engaging in the behaviour ("models"), interacting with the model and their tools, and sometimes stealing the freshly extracted resource. This also corresponds to an extended period of tolerance from the models. Yet the long-term effect of variation in experiences during this period on the technological efficiency of individuals is unknown for primate tool use, and no research has assessed the role of both the learner and the model(s) in generating individual differences. Using >680 hours of video spanning 25 years, we assessed whether experiences during the stone tool use social learning period ("early learning period"; ages 0-5) predicted the post-early learning period (ages 6+) technological efficiency in wild chimpanzees in Bossou, Guinea. We found that learners varied in how frequently they peered at the models whole nut-cracking bouts, how many learning opportunities their mothers presented, and the amount of tolerance and intolerance they experienced from all selected models. Learners who experienced more intolerance became less efficient tool users, whereas learners who were exposed to more social learning opportunities and tolerance became more efficient. Peering at the whole nut-cracking bout decreased subsequent efficiency, hinting at learners acquiring less efficient cultural components of the behaviour. Our findings highlight the role of social learning in the acquisition of stone tool use and support the view that social learning opportunities within a tolerant environment are key in explaining the emergence and maintenance of complex forms of primate technology. Significance StatementThe capacity and inclination to learn from others, along with social learning opportunities provided by tolerant groupmates, are thought to have enabled the evolution of technology in primates, including hominins. The influence of the learning period on long-term individual variation in technological efficiency remains unknown for non-human primates but has significant implications for cultural transmission and evolution. We provide longitudinal support for the hypothesis that exposure to social learning opportunities during development predicts subsequent technological efficiency. Moreover, we show that low amounts of intolerance, not just general tolerance, is key in the ontogeny of technological efficiency. Finally, we find aspects of behavioural acquisition relating to accurate transmission of cultural traits rather than to learning to use tools efficiently.