Monkeys may not be very different from us at all (photo by Emma Tecwyn)

  • Study finds first evidence of monkeys capable of making decisions based on probabilities
  • Human infants use the same ability to understand other people’s goals and preferences

Monkey See, Monkey Talk?

By Peter Boisseau
The Freelance Bureau

It wasn’t exactly a Planet of the Apes moment, but when researchers proved monkeys can reason about proportions and ratios, it opened up the kind of possibilities that would tickle the fancy of any Hollywood scriptwriter.

The study on statistical reasoning among capuchin monkeys found the first evidence that a monkey species is capable of making decisions on the basis of probabilities. In other words, monkeys know how to play the odds.

Researchers tested the monkeys using jars of desirable peanuts and undesirable pellets in different ratios to prove they can reason about relative amounts, as opposed to just making straightforward comparisons about quantities.

The study also demonstrated that the monkeys – like great apes – share a capability once thought to be uniquely human.

“It might be that they are not that very different from us at all,” said Daphna Buchsbaum, an assistant professor of psychology at the University of Toronto, who authored the study published online in Animal Cognition with Emma Tecwyn, a postdoctoral researcher.

Monkey see, monkey talk?

While it still leaves capuchin monkeys a long way from the talking hero apes and monkeys in the popular movie series, the type of intuitive ability they demonstrated in the lab tests is a building block for complex thinking, such as understanding cause and effect, as well as language.

The researchers say infants use the same ability to understand other people’s goals and preferences.

“I think the fact that monkeys do share this ability would make us potentially more optimistic that they might also be capable of more sophisticated social inferences,” said Buchsbaum. “While I personally think monkeys are unlikely to be capable of learning language, the ability to track probabilities is absolutely related to language learning.”

From an evolutionary point of view, there are more important applications for this ability in monkeys other than learning language, such as how to forage and compete for food successfully, she added.

Monkeys, apes and infants

The statistical reasoning abilities shared by human infants and monkeys are part of a broader range of cognitive skills that encompass everything from predicting the behaviour of others to being able to reason about someone’s desires and mental state.

Until recently, the ability to make inferences using probabilities was thought to develop relatively late in childhood. But recent work revealed this ability in infants as young as 10 months old.

Other research suggests that great apes such as chimpanzees, gorillas and orangutans also share this intuitive statistical ability with human infants.

What’s intriguing about the monkey study is it suggests that this ability developed earlier on the ancestral tree before apes and humans branched off, Tecwyn says.

Humans shared a common ancestor with chimps about six million years ago. But we last shared a common ancestor with capuchin monkeys about 30 million years ago. “So we could make the inference that this ability is at least that ancient,” says Tecwyn.

What makes us unique?

It is possible that statistical reasoning is a trait capuchins evolved independently, and it is not shared by other monkey species, adds Buchsbaum.

“But given that humans, apes and capuchins all share the trait, it is more likely that it evolved once earlier rather than independently in these different groups.”

Researchers have long been on a quest to establish what makes humans unique from other animals and conversely, what cognitive abilities are shared. Like the ape studies before it, the capuchin research further lays to rest the idea that probabilistic reasoning is one of the traits that makes humans unique.

Buchsbaum says an exciting avenue for future research would be investigating whether animals other than primates also share this ability to make intuitive statistical inferences, and whether non-human animals are capable of more sophisticated social reasoning often thought to be unique to humans.

“But regardless, within the broader animal kingdom, I don’t think we can doubt monkeys are pretty sensitive and intelligent animals,” Buchsbaum says.

©2017 Peter Boisseau

In an interesting development, a recent study suggested apes and monkeys have the vocal anatomy to produce clearly intelligible human speech. You can read more here or watch a video about it. On a sad note, Koko the gorilla, who became world famous after mastering sign language, recently died. -- Ed

Please contact us if you want publicity and/or earned media, we're here to help. For blog on the power of storytelling, please go here. -- Ed  

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Related Links 

Monkeys Play the Odds - University of Toronto Arts and Science 

Capuchin monkeys capable of statistical reasoning - U of T News