Travel fosters tool use in wild chimpanzees

Ecological variation influences the appearance and maintenance of tool use in animals, either due to necessity or opportunity, but little is known about the relative importance of these two factors. Here, we combined long-term behavioural data on feeding and travelling with six years of field experiments in a wild chimpanzee community. In the experiments, subjects engaged with natural logs, which contained energetically valuable honey that was only accessible through tool use. Engagement with the experiment was highest after periods of low fruit availability involving more travel between food patches, while instances of actual tool-using were significantly influenced by prior travel effort only. Additionally, combining data from the main chimpanzee study communities across Africa supported this result, insofar as groups with larger travel efforts had larger tool repertoires. Travel thus appears to foster tool use in wild chimpanzees and may also have been a driving force in early hominin technological evolution. DOI: http://dx.doi.org/10.7554/eLife.16371.001
eLife digest There is currently much debate about the origins of animal culture, including why some animals have acquired the ability to use tools. Ecological problems often lead to the innovation of new tools. For example, a particular desirable food item may not be reachable without using a tool, or environmental conditions may make it difficult for an animal to find food without help. Gruber et al. investigated how particular ecological factors influenced the use of tools in wild chimpanzees by combining controlled field experiments and observational data. When the ecological conditions were the most demanding, wild chimpanzees engaged most with the honey-trap experiment, an experiment where they had to use a tool to extract honey from a cavity dug in a log. Chimpanzees spent a longer time engaging with the apparatus when not much food was available and they had to travel more to obtain it. However, actual tool use during the experiments was only influenced by the travel effort made by the chimpanzees before they engaged with the log, not by how much fruit they had eaten beforehand. In a larger analysis that included data from all of the long-term field sites with habituated chimpanzees, Gruber et al. found that chimpanzee communities that travel further on a daily basis use a wider range of tools to acquire food. These results suggest that travel is an important factor to consider when studying how tool use evolved. Furthermore, these results can be extrapolated to humans, who both travel further and use a greater variety of tools than chimpanzees. Although innovation and culture are closely linked, innovation is mostly performed by individuals whereas culture is a social process. However, both are shaped by the environment. The next step will therefore be to disentangle and quantify the different contributions of environmental, individual and group factors in explaining how culture evolves. DOI: http://dx.doi.org/10.7554/eLife.16371.002