When Aristotle suggested that humans are distinct from other animals due to their ability to be rational, he implied that humans can form and re-evaluate views and beliefs based on evidence. This concept of rationality is highlighted by Jan M. Engelmann, an evolutionary anthropologist at the University of California, Berkeley, who emphasizes the importance of critically assessing our beliefs in light of available evidence.
Traditionally, in Western intellectual circles, rationality has been considered a uniquely human trait. To challenge this notion, Engelmann conducted a study to explore the presence of rational thinking in chimpanzees, and discovered that they exhibit rational behavior comparable to humans.
Food Puzzles
Engelmann notes, "There was quite a bit of research showing that chimpanzees can form their beliefs in response to evidence." These studies often involved scenarios where chimpanzees chose between two boxes, one of which contained a snack. When researchers shook both boxes, the chimps consistently opted for the box that produced a rattling sound.
However, Engelmann points out that prior research hadn't thoroughly explored the ability of chimpanzees to revise beliefs rationally. He sees belief revision as a critical aspect of rationality, aligning with insights from philosophy, psychology, and cognitive science. "There are so many irrational ways of responding to counter evidence," notes Engelmann, referring to the tendency to stick with previously held beliefs.
In their study, Engelmann and his team tested whether chimpanzees could revise their beliefs based on further evidence. Using the same experimental setup where animals chose between two containers, the study found that, after initially basing their choice on available evidence, chimpanzees were able to change their decision when presented with new evidence.
Complicated Choices
The researchers began by categorizing the evidence given to the chimpanzees as either weak or strong. Weak evidence included minor clues like crumbs around a container, whereas strong evidence directly suggested the presence of food, such as the rattling noises from earlier studies. The initial experiments involved presenting weak evidence for one container and strong evidence for another, while varying the order of the evidence presented to the chimpanzees.