Nut-cracking chimpanzees looked at the tools

Nut-cracking chimpanzees looked at the tools

Chimpanzee cracking nuts. © Liran Samuni/ Taï Chimpanzee Project

Sticks, stones, boulders: Chimpanzees use objects in their environment as tools to crack hard nuts. Which material and which technique they use can reveal something about the use of tools and cultural transmission among our early ancestors. Using groups of chimpanzees in the Ivory Coast and Guinea, biologists have now investigated which factors influence the great apes' nut-cracking technique.

Just as our ancestors did millions of years ago, some animals today use tools to augment their abilities. This, in turn, can also have an impact on their evolutionary development. "Tools used for cutting and hammering provided a competitive advantage in accessing diverse food sources, thereby influencing the cultural and biological evolution of our species," explain Tomos Proffitt of the Max Planck Institute for Evolutionary Anthropology in Leipzig and his colleagues.

Stone tool in check

It is all the more interesting to examine how our closest relatives use tools: the chimpanzee. It has long been known that these great apes developed special techniques, for example for cracking nuts. They do this by placing a nut on a hard surface and then hitting the nut with a tool such as a piece of wood or a stone to crack it open. Depending on the region and population, the chimpanzees use different objects as hammers and anvils.

Proffitt and his team have now investigated how the tools and nut-cracking techniques differ in different groups of free-living chimpanzees in West Africa in Tai National Park in the Ivory Coast and in Guinea. To do this, the researchers identified and scanned the hammer and anvil tools that the animals use to crack different types of nuts. By comparing the 3D models of these stone tools, they were able to determine how the tooling techniques of both chimpanzee populations differed.

Tools reflect nut type and material availability

The evaluation showed that the chimpanzees in the Tai forest looked for different stone hammers to crack depending on the type of nut: "The stone hammers used to process coula nuts are significantly smaller than those used to process panda and parinari nuts , while there are hardly any differences between the latter two,” report Proffitt and his team. The chimpanzees therefore recognize that they need large tools for the much harder panda and parinari nuts, while small stone hammers are sufficient for the softer coula nuts.

The analyzes also showed that the chimpanzees' nut-cracking leaves characteristic marks on their tools. Similar to the archaeological relics of our ancestors, these reflect their technique and choice of materials. For example, the stone hammers of the chimpanzees in the Tai National Park showed significantly fewer knocking surfaces than those of their relatives in Guinea. The biologists attribute this to the fact that the great apes in Guinea have fewer choices when it comes to material and therefore do not always find optimally hard stones as hammers. The boulders that both chimpanzee groups used as anvils, on the other hand, were very similar in the pattern of their traces of use. The anvil stones were mostly on larger boulders anchored in the ground, which were located near nut trees.

look into our past

According to the researchers, these insights into chimpanzee nut-cracking technology also shed light on how our ancestors developed tool techniques more than three million years ago. "By understanding what this simple stone tool technology looks like and how it varies between groups, we can begin to understand how we can better identify this signature in the earliest hominin archaeological record as well," explains Proffitt.

Source: Max Planck Institute for Evolutionary Anthropology, Article: Royal Society Open Science; doi: 10.1098/rsos.220826

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