Two chimpanzees that showed their skills on Ngamba Island, Uganda
Esther Herrmann
We are no longer the only animal known to think ahead and prepare for two possible futures – chimps can do it too.
If you are unsure whether it will be sunny or raining later, you might grab sunscreen and an umbrella before you leave home. This ability to consider different eventualities, known as modal reasoning, is essential to human cognition.
It was thought that other animals couldn’t manage the feat, including our closest living relatives, chimpanzees. This is in part because a 2017 study found that the primates lack the capacity to prepare for mutually exclusive outcomes.
The results weren’t accepted by all, though, because the study expected the chimpanzees to use behaviours that don’t come naturally to them, says Jan Engelmann at the University of California, Berkeley.
“To demonstrate competence, they had to cover both exits of a Y-shaped tube with the palms of their hands,” he says. “I’ve worked for 12 years with chimpanzees now, and I’ve never seen them show this behaviour.”
Now, Engelmann and his colleagues have tried an alternative method relying on behaviour that comes more naturally to the animals.
Working at Ngamba Island Chimpanzee Sanctuary in Uganda, where the animals can roam in 95 acres of forest, the researchers put individual chimps in front of two tilting platforms, each with a piece of food on it. The first version of the experiment used an opaque cylindrical tube above one of the platforms, through which the team would drop a rock.
If the chimpanzee didn’t intervene, the food would fall, but if it stabilised the platform with its hands, it was given the food as a reward. In this scenario, the 15 chimpanzees only stabilised the platform they knew the rock would hit.
The second experiment used an opaque inverted Y-shaped tube with an exit 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 steady both platforms to protect both pieces of food.
“To my knowledge, they’re the first [non-human] animals who demonstrate competence in a task measuring the representation of alternative possibilities,” says Engelmann.
Some evidence suggests that children aged between 1 and 2.5 years can consider mutually exclusive outcomes, says team member Mariel Goddu at Harvard University. But there are researchers who argue that these abilities don’t develop until the age of 4, when children are able to talk about multiple possibilities. The chimpanzee findings support the earlier age range, showing that this ability may not be dependent on language, she says.
“The representation of alternative possibilities is fundamental to many cognitive capacities that humans are proud of, like creativity and morality,” says Engelmann. “It’s quite exciting to think that there might be an evolutionary history to this ability as well.”
“I am not at all surprised that chimpanzees are capable of modal reasoning, but it is great to see confirmation of these abilities using non-invasive cognitive experiments,” says Ammie Kalan at the University of Victoria in Canada. This study shows how taking the time to appreciate chimpanzees’ natural behaviour can help us challenge results from studies in captive animals, she says.
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