Chimpanzees act as 'engineers', choosing materials to make tools based on structural and mechanical properties

These findings, published in the journal iScience, have important implications for understanding the technical abilities associated with the making of perishable tools -- a topic which remains a highly unknown aspect of human technological evolution.

Termites are a good source of energy, fat, vitamins, minerals and protein for chimpanzees. To eat the insects, chimpanzees need to use relatively thin probes to fish the termites out of the mounds where they live. Given that the inside of the mounds is made up of winding tunnels, the scientists hypothesized that using flexible tools would be more effective for chimpanzees at fishing out the insects than using rigid sticks.

To test this, first author Alejandra Pascual-Garrido took a portable mechanical tester to Gombe and measured how much force it took to bend plant materials used by the apes compared to plant materials that were available but never used. Findings showed that plant species never used by chimpanzees were 175 percent more rigid than their preferred materials.

Furthermore, even among plants growing near termite mounds, those that showed obvious signs of regular use by the apes produced more flexible tools than nearby plants that showed no signs of use.

"This is the first comprehensive evidence that wild chimpanzees select tool materials for termite fishing based on specific mechanical properties," says Alejandra Pascual-Garrido, who has been studying the raw materials used in chimpanzee tools in Gombe for more than a decade.

Notably, certain plant species, such as Grewia spp., also constitute tool material for termite fishing chimpanzee communities living up to 5,000 kilometres away from Gombe, implying that the mechanics of these plant materials could be a foundation for such ubiquitous preferences, and that rudimentary engineering may be deeply rooted in chimpanzee tool-making culture.

Wild chimpanzees may therefore possess a kind of "folk physics" -- an intuitive comprehension of material properties that helps them choose the best tools for the job.

Their natural engineering ability is not just about using any stick or plant that is available; chimpanzees specifically select materials with mechanical properties that can make their foraging tools more effective.

Dr Alejandra Pascual-Garrido, Research Affiliate at the School of Anthropology and Museum Ethnography, University of Oxford, said: 'This novel approach, which combines biomechanics with animal behaviour, helps us better understand the cognitive processes behind chimpanzee tool construction and how they evaluate and select materials based on functional properties'.

The findings raise important questions about how this knowledge is learned, maintained and transmitted across generations, for example, by young chimpanzees observing and using their mothers' tools, and whether similar mechanical principles determine chimpanzees' selection of materials for making other foraging tools, such as those used for eating ants or harvesting honey.

'This finding has important implications for understanding how humans might have evolved their remarkable tool using abilities,' explains Adam van Casteren, Department of Human Origins, Max Planck Institute for Evolutionary Anthropology, a specialist in biomechanics and evolutionary biology. 'While perishable materials like wood rarely survive in the archaeological record, the mechanical principles behind effective tool construction and use remain constant across species and time'.

By studying how chimpanzees select materials based on specific structural and/or mechanical properties, we can better understand the physical constraints and requirements that would have applied to early human tool use. Using such a comparative functional framework provides new insights into aspects of early technology that are not preserved in the archaeological record.