Bonobos can imagine and pretend, study finds by staging a tea party
Can animals play pretend? It took a snack with a bonobo to find out.
In a series of experiments, a team of researchers offered a bonobo named Kanzi invisible juice and grapes, presenting the tests as a kind of game, similar to an imaginary snack for a child.
The results, published Thursday in the journal Science, show that Kanzi could play the game. The researchers concluded that the primate could imagine and follow the invisible juice poured between a pitcher and bottles.
“It’s able to track and locate a fake object, but at the same time it understands that it’s not actually there,” said Chris Krupenye, study author and assistant professor of psychology and brain sciences at Johns Hopkins University.
In the past, scientists believed that the ability to pretend and consider multiple realities was unique to humans. But other observations of primates behaving as if they were pretending – young chimpanzees playing with a “log doll” or moving imaginary blocks – have called this idea into question. The new study provides the first evidence of an animal simulating a situation that researchers could control.
“We view our ability to imagine other worlds or other objects, or to imagine futures, as one of those rich features of human mental life that are presumed to be unique to our species,” Krupenye said. But apes “may share some of the fundamental cognitive machinery that will enable at least some degree of imagination.”
For the new study, the researchers modeled the experiences after common tests of childhood development.
“In the first years of life, you see children engaging in pretend play,” Krupenye said — behaviors like having imaginary friends or snacks with stuffed animals. “Many studies in child psychology have focused on these kinds of scenarios. »
The researchers set up three experiments for Kanzi. First, they took out an empty, transparent pitcher and two empty, transparent bottles. A researcher poured imaginary juice from the pitcher into the two glasses, then poured a glass of fake juice into the pitcher. Then they would ask Kanzi to point out where the juice was.
Kanzi pointed to the cup that would still have had juice in it, if it had been real, 34 times out of 50, or 68 percent of the time. This is a common “success rate” in cognitive tests in monkeys, according to Krupenye.
In the second experiment, the researchers presented Kanzi with a cup of real juice next to a cup of fake juice and asked him which one he wanted. He showed the glass of juice 14 out of 18 times, confirming that Kanzi could distinguish real juice from fake.
Ultimately, the researchers performed another version of the original test, but using imaginary grapes instead of juice, with similar results.
Taken together, the experiments suggest that Kanzi was able to distinguish an imagined scenario from current reality and keep both in mind.
“This is really a very important step in our understanding of how nonhuman primates think,” said Jan Engelmann, an associate professor of psychology at the University of California, Berkeley, who was not involved in the study.
Engelmann said the experiments strengthen evidence that monkeys can engage in “secondary representations” – cognitive processes in which the mind models multiple scenarios, including hypothetical scenarios – and conduct complex thought processes such as planning, reasoning and inferring cause and effect. Such behaviors provide an evolutionary advantage.
“You can then test things in imagination before you do them in real life,” said Kristin Andrews, a philosophy professor at the CUNY Graduate Center who studies animal minds. “You can determine whether you should do it or not.”
Andrews, who was not involved in the Kanzi study, said the results were compelling.
“If we did a study like this on human children, we would draw the same kinds of conclusions,” she said. “This is reminiscent of classic studies of human children, in which they use a banana as a telephone.”
Kanzi, who died last year at age 44, was a unique bonobo. Born in captivity, he was the first bonobo to understand certain elements of spoken English. He learned the language by learning symbols representing words, called lexigrams, which he used to communicate with his keepers.
Kanzi learned elements of the language from a young age.
“Kanzi, when he was a baby, was right on top of his mother, clinging to his mother’s body while she practiced these lexigrams, and she wasn’t doing very well,” Krupenye said. “He had absorbed all this knowledge from the beginning, and so they shifted the research program to Kanzi and another bonobo, Panbanisha.”
Later in his life, Kanzi was able to identify several hundred lexigram symbols, for objects like “egg” and activities like “pursuit”. He could respond to some English prompts by pointing to lexigrams.
Bonobos are humanity’s closest living genetic relative. Krupenye and his study co-authors therefore suggest that the ability to pretend and imagine was likely present 6 to 9 million years ago, when the two species diverged during evolutionary history.
However, it is not yet clear whether other non-human primate species, or even other bonobos, would perform as well as Kanzi on the tests. The new study notes that Kanzi’s lexigram training could have led him to better recognize symbols and that his language training could have changed his brain.
It’s possible that “we can only exploit this ability because Kanzi has language, but all monkeys have this ability” to pretend, Engelmann said. “Another option is that the language gives Kanzi a new ability.”
Overall, the more scientists study animals, the more they learn that many things once thought to make humans exceptional are more widely shared, Andrews said.
Some scientists are even putting forward a new hypothesis: that individual human cognition may not be significantly more powerful than that of chimpanzees, from an individual point of view. Instead, what might make humans special is their exceptional social skills and ability to collaborate.
“What humans are really good at is social rationality, social cognition and thinking with others,” Engelmann said. “Language is an adaptation that allows us to do this. »
