An experimental study of modern chimpanzees has documented patterns of behavior that seemingly mirror those of our prehistoric human ancestors, casting light on how our predecessors may have utilized tools.

The study, published in the Journal of Human Evolution, demonstrates that the process used by a group of chimps to select stones for use as tools appear to resemble what is documented for Oldowan hominins.

This term refers to early human ancestors who are associated with the Oldowan stone tool industry. (Hominins are a group of species that includes modern humans plus all our extinct ancestors and relatives since the split from the common ancestor we share with chimpanzees.)

The Oldowan tools -- dated to between 2.9/2.6 million and 1.7 million years ago -- are among the first to be used by early hominins. There is evidence though for even earlier tool use stretching back more than 3 million years ago. The origins of this technology remain the subject of significant debate.

"Humans have been able to use technology to conquer virtually every terrestrial habitat on the planet. This is largely the result of our ability to use tools. However, we don't know when humans really became dependent on these tools," study author David Braun, with the Max Planck Institute for Evolutionary Anthropology in Germany, told Newsweek.

Recent research has indicated that tool use may have very deep roots among hominoids -- the group of primates that includes gorillas, chimpanzees, orangutans, gibbons, bonobos and humans. This is perhaps not surprising given that there are numerous examples of tool use as an adaptive strategy in the animal kingdom today, particularly among primates.

The use of tools is shared by humans and our closest relatives, chimpanzees, for example. There is also evidence to suggest that chimps have the ability to take into account certain physical properties of stones -- such as size and weight -- when selecting rocks for use as task-appropriate tools.

This raises intriguing parallels to studies of Oldowan technology, which have highlighted how modern human ancestors selected specific rocks for tool manufacture based on distinct properties of the rocks, such as their ability to fracture and be resistant to wear.

In the latest study, the researchers wanted to investigate the patterns of stone tool selection for the purposes of cracking nuts by wild chimpanzees at Bossou in Guinea -- a country in West Africa. This group of chimps are well-known for their diverse range of tool-use behaviors -- in particular, their distinctive utilization of moveable rocks as hammers and anvils to crack open oil palm nuts.

"[Study author Susana Carvalho] and I have been interested in the origins of technology for several decades. We have been able to show that humans over 2 million years ago could understand the differences in rock types and selected specific rock types. However, it was impossible to understand how they knew this," Braun said.

"We wanted to observe the decision-making. Since we knew that chimpanzees seem to understand rock mechanics we wanted to see if we could observe their decisions regarding rocks that they had never seen before."

In order to do this, the team collected rocks from western Kenya -- where there is a wide diversity of stones available -- and shipped them to Guinea, before carrying them out to the forest.

"We had already conducted extensive mechanical tests on these stones so we knew how they were different. We also knew that many of them looked alike even if they had different mechanical properties," Braun said.

The researchers then placed the stones out in a random order and waited for the chimpanzees to select rocks. Over the next six weeks, the team observed the chimps cracking nuts, documenting each each time they selected a stone, and how often they used different ones.

"In particular, we documented how often they used particular stones relative to how often that rock was available. We did this first with two rock types that were very different and then gradually introduced more rocks to see if the chimpanzees could identify subtler differences," Braun said.

One of the key findings was that the chimps were able to identify certain characteristics of the stones and use them for specific tasks. For example, they used softer stones as anvils because if they used harder rocks the nuts would slip off the anvils. And they used harder stones for hammers because this meant they could crack nuts more efficiently.

It became clear that over the course of the six weeks, the chimps had effectively figured out the best rocks to use for each task involved in nut-cracking.

"Sometimes they did this through trial and error. Sometimes they did this through using stones that other chimpanzees had used," Braun said.

The patterns of selection (i.e. how selective the chimpanzees were) is very similar to that which scholars have seen in the archaeological record for early humans more than 2 million years ago.

"This suggests that early humans may have been able to use similar trial and error as well to determine the best stones," Braun said.

"If this was combined with copying from the other individuals in their group then early humans [could] very quickly identify and use the best tools for certain tasks. In other words, all early humans don't need to understand mechanical properties. Only a few of them need to and then they could watch each other and determine the best options."

"This 'learning from others' capacity is one of the truly human superpowers. It appears that chimpanzees also learn key details of tool use from each other. This may mean that some of the underlying capacities of tool use are present in our closest living relatives (chimpanzees)," he said.

The results suggest that tool use -- as well as learning about tool use from other members of your group -- may be a feature of many different primate groups.

"We tend to think that tools separate us from other animals but in fact using tools and learning about tools from others seems to be a generalized trait of primates that we share with many other members of the primate order," Braun said.

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Braun, D. R., Carvalho, S., Kaplan, R. S., Beardmore-Herd, M., Plummer, T., Biro, D., & Matsuzawa, T. (2024). Stone selection by wild chimpanzees shares patterns with Oldowan hominins. Journal of Human Evolution, 199, 103625. https://doi.org/10.1016/j.jhevol.2024.103625