Implementing long-term baselines into primate tool-use studies

Naïve, adult, captive chimpanzees do not socially learn how to make and use sharp stone tools

Although once regarded as a unique human feature, tool-use is widespread in the animal kingdom. Some of the most proficient tool-users are our closest living relatives, chimpanzees. These repertoires however consist primarily of tool use, rather than tool manufacture (for later use). Furthermore, most populations of chimpanzees use organic materials, such as sticks and leaves, rather than stones as tools. This distinction may be partly ecological, but it is also important as chimpanzees are often used as models for the evolution of human material culture, the oldest traces of which consist of manufactured sharp stone tools (so-called "flakes"). Thus, examining the conditions (if any) under which chimpanzees may develop flake manufacture and use can provide insight into the drivers of these behaviours in our own lineage. Previous studies on non-human apes' ability to make and use flakes focused on enculturated apes, giving them full demonstrations of the behaviour immediately, without providing social information on the task in a stepwise manner. Here we tested naïve, captive chimpanzees (N = 4; three potentially enculturated and one unenculturated subject) in a social learning experimental paradigm to investigate whether enculturated and/or unenculturated chimpanzees would develop flake making and use after social information of various degrees (including a human demonstration) was provided in a scaffolded manner. Even though social learning opportunities were provided, neither the unenculturated subject nor any of the potentially enculturated subjects made or used flakes, in stark contrast to previous studies with enculturated apes. These data suggest that flake manufacture and use is outside of our tested group of captive chimpanzees' individual and social learning repertoires. It also suggests that high levels of enculturation alongside human demonstrations (and/or training) may be required before captive chimpanzees can develop this behaviour.

Captive great apes tend to innovate simple tool behaviors quickly

Recent studies have highlighted the important role that individual learning mechanisms and different forms of enhancenment play in the acquisition of novel behaviors by naïve individuals. A considerable subset of these studies has focused on tool innovation by our closest living relatives, the great apes, to better undestand the evolution of technology in our own lineage. To be able to isolate the role that individual learning plays in great ape tool innovation, researchers usually employ what are known as baseline tests. Although these baselines are commonly used in behavioral studies in captivity, the length of these tests in terms of number of trials and duration remains unstandarized across studies. To address this methodological issue, we conducted a literature review of great ape tool innovation studies conducted in zoological institutions and compiled various methodological data including the timing of innovation. Our literature review revealed an early innovation tendency in great apes, which was particularly pronounced when simple forms of tool use were investigated. In the majority of experiments where tool innovation took place, this occurred within the first trial and/or the first hour of testing. We discuss different possible sources of variation in the latency to innovate such as testing setup, species and task. We hope that our literature review helps researchers design more data-informed, resource-efficient experiments on tool innovation in our closest living relatives.