
The basic ability to understand language and develop technology may have evolved before humans and apes diverged millions of years ago, according to a study published in the journal PeerJ.
Most human behaviours are more complex than those of other animals, including the ability to use spoken language and make tools. These skills often involve a sequence of steps and the ability to understand relationships between different elements. For example, making a simple cup of tea consists of a sequence of steps in a particular order, such as boiling the kettle before pouring the water onto a cup. Humans organise their thoughts to solve each step in order: boil kettle, put tea bag in a cup, pour water, etc. Importantly, we can add separate actions if needed, such as cleaning up some spilled milk.
For a long time, it was believed that this ability to be flexible was unique to humans, but a new study shows that this may not be the case. In this new study, the team investigated the actions of wild chimpanzees—our closest relatives—while they were using tools. The aim was to see if these were organized into sequences with similar properties rather than just reflex responses.
Using video footage of chimpanzees in the Bossou forest, Guinea, the team watched the animals crack hard-shelled nuts using a hammer and anvil stones. This is one of the most complex tools any animal uses in the wild.
The team recorded the sequence of actions that chimps performed —grasp nut, pass through hands, place on anvil, crack nut —for over 300 nuts. Results showed that chimpanzees followed a sequence of actions similar to humans. About half of the chimpanzees used actions much further along the sequence than expected if actions were simply linked together one step at a time. This proves that chimpanzees not only plan their action sequences but can adjust their performance if needed to get the desired result.
“The ability to flexibly organise individual actions into tool use sequences has likely been key to humans’ global success. Our results suggest that the fundamental aspects of human sequential behaviours may have evolved prior to the last common ancestor of humans and chimpanzees, and then may have been further elaborated on during subsequent hominin evolution,” said Dr Elliot Howard-Spink from the Max Planck Institute of Animal Behavior.
“There is increasing recognition that preserving cultural behaviours in wild animals – such as stone-tool use in West-African chimpanzees – should be incorporated into conservation efforts. Wild chimpanzees and their cultures are critically endangered, yet our work highlights how much we can yet learn from our closest relative about our own evolutionary history,” added Professor Dora Biro from the University of Rochester.
The authors now want to understand how these sequences emerge, but they could involve behaviours such as chimpanzees pausing to think and readjust tools before continuing or collecting several nuts and then cracking them in one long sequence.
The results also suggest that although the majority of chimpanzees can organise actions similarly to humans, through the same repeatable steps, not all not all animals can achieve this. This variation between individuals may suggest that these strategies for organising behaviours may not be universal in the same way they are for humans.
“There has been a renewed interest in the co-evolution of language and stone tool use in human evolution, and our study contributes to this debate. While the connection between our results and early hominin stone tool use can be made more readily, how this connects with the evolution of other complex behaviours, like language, remains an exciting avenue of future research,” concluded Professor Thibaud Gruber from the University of Geneva.
Howard-Spink E, Hayashi M, Matsuzawa T, Schofield D, Gruber T, Biro D. 2024. Nonadjacent dependencies and sequential structure of chimpanzee action during a natural tool-use task. PeerJ 12:e18484 https://doi.org/10.7717/peerj.18484