The human capacity for rational thinking makes us unique among the animal kingdom, according to wise, old Aristotle. However, an ever-growing body of research suggests that rationality might not be quite as distinctive a human quality as we might have thought.
In a study recently published in the journal Science, researchers at the Ngamba Island Chimpanzee Sanctuary in Uganda presented chimpanzees with two boxes: one with food and one without a snack. They were initially given a clue as to which one had food. The team then provided the chimps with sequential clues of varying strength about which one contained a snack.
“When the initial evidence was strong, the chimpanzees stuck with their original choice; when the new evidence clearly outweighed the first, they switched their choice,” Hanna Schleihauf, an assistant professor in developmental psychology at Utrecht University and co-author of the study, tells Popular Science.
Schleihauf and her colleagues also incorporated computer models to confirm that the chimpanzee’s responses matched up with rational strategies of belief revision. In other words, they made sure the primates were practicing genuine reasoning and not, for example, simply favoring the most recently presented evidence. Researchers typically associate this sort of reasoning with children around four-years-old.
“Most strikingly, the chimps also showed metacognitive sensitivity to evidence,” Schleihauf continued. Metacognition is awareness and understanding about our thinking processes.
“They not only adjusted their choices, but did so in ways that suggest they tracked the evidential basis of their beliefs: when earlier evidence was defeated, they revised their belief accordingly,” she explains. “This indicates that belief revision based on weighing evidence—a key hallmark of rationality long considered uniquely human—is also present in chimpanzees.”
The study also suggests that there isn’t as sharp a difference between human and animal cognition as we once believed. It’s more akin to a gradual continuum of rational reasoning, Schleihauf says.
However, this study provides more than just an interesting discovery about one of our closest primate relatives. According to the team, the results have several practical applications.
For example, “demonstrating rational belief revision in chimpanzees provides a powerful comparative baseline for understanding the evolution of human reasoning,” said Schleihauf. By identifying which aspects of rationality humans share with chimps versus which are unique to us, researchers can better recognize which, “develop early in children, which depend on culture, and which rely on uniquely human forms of social learning such as teaching or argumentation.”
She adds that the study is important for animal conservation and welfare because it further justifies the protection of great apes, the increased ethical norms in research and conservation, and the creation of more cognitively stimulating habitats in sanctuaries and zoos.
Ultimately, the paper joins a host of recent research suggesting that humans simply aren’t as unique as we thought.