A recent study led by the University of Oxford and the Max Planck Institute for Animal Behavior has revealed that wild chimpanzees are capable of organizing their actions into complex sequences similar to human behaviors. The research, published in the journal PeerJ, suggests that unique behavioral traits characteristic of humans, which are the basis of language and technological culture, may have formed before the divergence of humans and chimpanzees. "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, according to Science Daily.
The study focused on one of the most complex actions performed by primates: nut cracking using stone tools. In the forests of the village of Bossou in Guinea, chimpanzees form an isolated community and use stones as hammers and anvils to crack hard-shelled nuts, accessing the nutritious kernels inside. Over 25 years, the researchers observed 21 chimpanzees aged 6 to 60 years, analyzing 3,882 nut-cracking attempts and recording sequences totaling around 8,260 actions for over 300 nuts, which included actions like "grab," "pour," "turn," and "spill."
The analysis revealed that chimpanzees are capable of linking separate elements of their actions, even if time passes between them. For example, they may pause sequences to readjust tools before continuing the task. The researchers reported, "Half of the adult chimpanzees seemed to associate actions that were much further along in the sequence than expected." This suggests that the majority of chimpanzees organize actions similarly to humans through repeatable "chunks."
Using advanced statistical models, the researchers identified relationships between the sequential actions of chimpanzees that resemble those found in human behaviors. These sequences involve breaking down tasks into manageable blocks and recognizing connections between actions that are distant in the process, which are necessary for organizing actions into complex sequences. These observations challenge our understanding of animal cognitive abilities and indicate the primates' capacity for flexible thinking.
However, the results of the study do not apply to all observed chimpanzees, indicating that the skills for organizing actions into complex sequences are not universal among chimpanzees as they are among humans. This variability in behavior may indicate differences in cognitive abilities among chimpanzees. Some chimpanzees were more efficient at nut cracking than others, even when they were of the same age and sex. These differences between individual chimpanzees were consistent over time.
They found that older chimpanzees required more strikes and time to crack the shells than younger ones, possibly due to less strength and the need for more breaks. However, older chimpanzees less frequently let the object slip away during cracking attempts, which the research team suggests could be due to their years of experience with their cracking method.
"Being more efficient at cracking nuts has advantages for the chimpanzees: with less energy expenditure, they obtain more food, which may provide an evolutionary advantage," the researchers explained, as reported by Popular Science. They suspect that the different use of tools within a group could have evolutionary implications, and possible deficiencies in nutrient supply could lead some individuals to die earlier.
"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," said Professor Thibaud Gruber, according to Science Daily. The ability to flexibly organize individual actions into sequences that include the use of tools has probably been the key to human global success. Understanding how these relationships emerge during action organization will be a key goal for future research.
"It is increasingly recognized that the protection of cultural behaviors of wild animals—such as the use of stone tools by chimpanzees in West Africa—should be included in conservation efforts. Wild chimpanzees and their cultures are critically endangered, and our research highlights how much we can still learn from our closest relative about the history of our own evolution," added Professor Dora Biro, a co-author of the publication, according to Science Daily.
The researchers plan to investigate how actions are grouped into higher-order chunks by chimpanzees during tool use. They also want to explain the principles that guide chimpanzees when creating their tool-related behaviors. This research will aim to clarify the rules that chimpanzees follow when generating their tool-use behaviors, which could help the interdisciplinary field of primate archaeology understand the evolutionary role of tools in humans and non-human primates.
Since many great apes perform dexterous and technical foraging behaviors, it is plausible that the capacity for complex sequences is shared across ape species. Understanding how these structures emerge during development and are shaped across adult lives will be a key focus of future studies.
The article was written with the assistance of a news analysis system.