For decades, scientists have been studying the cognition of great apes to understand how our own complex cognitive abilities evolved. Much of the research is based on the idea that if a particular ability—like using gestures to communicate —is found only in species that are closely related to us, then it's likely that the trait appeared relatively late in our evolutionary history .
But these interpretations see cognition as static—and uniform within a particular species. In reality, great apes, like humans, have cognitive abilities that develop, wax, and wane throughout their lifetimes. These abilities also likely vary between individual apes as different personalities and life experiences shape cognitive ability.
"There's a lot of experiences that … contribute to the precise nature of how [an individual's] cognition is structured and organized," said Manuel Bohn, a developmental psychologist at Leuphana University of Lüneburg. "We very much have these kind of developmental and individual differences perspectives for humans. And so, we thought this was clearly missing in great apes."
In a new study published in Psychological Science , which builds upon a 2023 study by Bohn and his colleagues, researchers assessed how a range of cognitive abilities differed between individual great apes over an extended period of time. The research not only found that cognition consistently varied between individuals, it also revealed just how much researchers have yet to understand about the fundamental structure of great ape cognition.
To gain these conclusions, Bohn and colleagues studied 48 individual great apes. This sample comprised four species, ranging in age and sex: bonobos, chimpanzees, gorillas, and orangutans. The apes participated in a series of six cognitive tests over a period of a year and a half, including tasks like seeing if apes could follow the attention of a human experimenter, understand communicative cues, and remember where they searched for food. These tasks were based on past procedures that comparative psychologists have used in research to test for social cognition , reasoning , and executive function in great apes.
The study found that there was a substantial amount of variation between individual apes, even among the same species. Variables like what group an ape belongs to, its previous experience with research, sex, and rearing were strong predictors of performance. In addition, these individual differences in cognitive performance were relatively stable over the course of the study for most tasks.
"That's also often the way that we think about individual differences in humans, like they are stable traits or some property of an individual. And we find pretty good evidence that this is the case here in great apes as well," Bohn said.
Researchers also analyzed how performance on various tasks correlated with one another to understand how parts of ape cognition are related and structured. Interestingly, the results from tasks that relied on social cues (i.e., attention following) were not correlated with one another; high performance on one did not mean high performance on another. By contrast, most results from tasks that were nonsocial (i.e., reasoning) were solidly correlated.
This deviates from the cognitive structure that we know of in humans. "We do not find these clusters that we expect to be there from a human perspective, which I think is really interesting and thought-provoking," Bohn said. "If it's not this, then what is the structure of all of this?"
Bohn emphasized that though the sample size of the new research is small, it opens up questions that researchers could continue to investigate. He noted that future research could more rigorously assess the tools that researchers use to measure great ape cognition and seek to understand whether these tools are measuring the appropriate parts of cognition.
"We don't have assessment tools that have been particularly built to assess the different aspects of great ape cognition," Bohn said.
He also noted the need for longitudinal studies, although he acknowledged that these studies are often difficult to execute. But taking on the challenge could allow scientists to track and document cognitive development and how developmental progress varies between individuals. By comparing these findings with human development, it may be possible to understand the drivers behind great ape cognition and how it varies from our own.
"Think about these alternative structures of cognition," Bohn said. "What are the lines along which we can think about cognition being structured, other than the ones that we put in place for humans? [This study] is an invitation to think along those lines."
References
Bohn, M., Völter, C. J., Hanus. D., Eisbrenner, N., Eckert, J., Holtmann, J., & Haun, D. (2026). Individual differences in great ape cognition across time and domains: stability, structure, and predictability . Psychological Science, 37(5), 331–346.
Bohn, M., Eckert, J., Hanus, D., Lugauer, B., Holtmann, J., & Haun, D. B. M. (2023). Great ape cognition is structured by stable cognitive abilities and predicted by developmental conditions . Nature Ecology & Evolution, 7, 927–938.
