We are no longer the only animal known to think ahead and prepare for two possible futures: chimpanzees can do it too.
If you are not sure if it will be sunny or rainy later, you can take sunscreen and an umbrella before you leave the house. This ability to consider different eventualities, known as modal reasoning, is essential to human cognition.
Other animals were thought to be unable to accomplish the feat, including our closest living relatives, the chimpanzees. This is partly because a 2017 study found that primates lack the capacity to prepare for mutually exclusive outcomes.
However, the results were not accepted by everyone, because the study expected the chimpanzees to use behaviors that are not natural to them, he says. Jan Engelmann at the University of California, Berkeley.
“To demonstrate proficiency, they had to cover both outlets of a Y-shaped tube with the palms of their hands,” he says. “I have worked for 12 years with chimpanzees and I have never seen them display this behavior.”
Now Engelmann and his colleagues have tested an alternative method that relies on more natural behavior in animals.
Working in Ngamba Island Chimpanzee Sanctuary In Uganda, where the animals can roam 95 acres of forest, the researchers put individual chimpanzees in front of two tilting platforms, each with a piece of food on top. The first version of the experiment used an opaque cylindrical tube on one of the platforms, through which the team would drop a stone.
If the chimpanzee did not intervene, the food would fall off, but if he stabilized the platform with his hands, the food was given as a reward. In this scenario, the 15 chimpanzees only stabilized the platform they knew the rock would hit on.
The second experiment used an opaque tube in the shape of an inverted Y with an outlet above each platform. Not knowing which platform the rock was going to hit meant the chimpanzees behaved differently. Thirteen of the 15 were more likely to cover their bases and stabilize both platforms to protect both pieces of food.
“As far as I know, they are the first [non-human] animals that demonstrate competence in a task that measures the representation of alternative possibilities”, says Engelmann.
Some evidence suggests that children between the ages of 1 and 2.5 may consider outcomes mutually exclusive, says a member of the team Mariel Goddu at Harvard University. But some researchers argue that these skills don’t develop until age 4, when children can talk about multiple possibilities. The chimpanzee findings support the earlier age range, showing that this ability may not depend on language, she says.
“The representation of alternative possibilities is central to many cognitive abilities that humans are proud of, such as creativity and morality,” says Engelmann. “It’s quite exciting to think that there could be an evolutionary history for this ability as well.”
“I’m not at all surprised that chimpanzees are capable of modal reasoning, but it’s great to see confirmation of these abilities using non-invasive cognitive experiments,” he says. ammie kalan at the University of Victoria in Canada. This study shows how taking the time to appreciate the natural behavior of chimpanzees can help us challenge the results of captive animal studies, she says.
