Children and Monkeys Share a Common Understanding of Geometry

With their ability to use tools, remember faces and even learn how to communicate with humans through sign language, non-human primates are considered to be among the smartest creatures on earth. However, some concepts — geometry, for instance — have traditionally been thought of as beyond the abilities of humanity’s closest cousins.

But a new study published today in Proceedings of the National Academy of Sciences calls that prevailing notion into question.

“What surprised us wasn’t just that monkeys could do the task,” said Jessica Cantlon, a cognitive neuroscientist in Carnegie Mellon University’s Department of Psychology and Neuroscience Institute and senior author of the study. “It was that monkeys, children and adults seemed to think about geometric relationships in fundamentally the same way. That suggests these intuitions are part of the basic architecture of the primate mind.”

To come to this conclusion, Cantlon and her team offered olive baboons and Rhesus macaques nutritious fruit snacks in exchange for participation in a touch-screen matching game of two-dimensional geometric shapes.

“That might seem easy, but it’s actually pretty difficult, because there are no distinctive features among the objects, no major differences in color, or size or form,” said Cantlon, who is also the Ronald J. and Mary Ann Zdrojkowski Professor of Developmental Neuroscience/Psychology at CMU's Dietrich College of Humanities and Social Sciences.

Rather, the monkeys had to find the correct match based on geometric similarity alone.

“You’d get tripped up, too,” said Cantlon, when asked if an adult human would have trouble with the matching game.  

In fact, the researchers also performed the same experiment with dozens of preschoolers (ages 3 to 6) at CMU’s Children’s School, a laboratory school based in Dietrich College of Humanities and Social Sciences, as well as 79 adults from Bolivia’s indigenous Tsimane’ people. As a farmer-forager group, the Tsimane’ do not undergo the same sort of formal schooling found in the United States. Twenty-one American adults were also tested.

“That allowed us to sort of tease apart age and cultural experience,” said Cantlon. “Because sometimes when you’re trying to study something in children, it can be difficult to untangle whether their ability is developmental or something learned from education or experience.”

In the end, the researchers discovered that across all of the groups — two species of non-human primates, human children and adult humans — there was clear continuity in terms of how primates and humans thought about basic geometry.

“Geometric intuition is something humans eventually turn into mathematics and science,” said Cantlon. “So if we want to understand how children learn geometry, we need to understand what they bring to the table before formal instruction begins. This study suggests that children start with deep, evolutionarily ancient intuitions about shape and space. Education can build on those intuitions instead of treating geometry as something that has to be taught from scratch.”

The Primate Portal

The new study is only the most recent to come out of Cantlon’s lab in conjunction with what’s known as the Primate Portal.

Located at the Seneca Park Zoo in New York, the Primate Portal is collaborative project between a group of scientists at Carnegie Mellon University and the Rochester Institute of Technology who study the origins and nature of thought. It features an enclosed touchscreen that captive olive baboons have the option of interacting with while going about their normal daily activities.

“One of the baboons, named Kalamata, was the hardest working monkey that I’ve ever seen,” said Jialin Li, a second-year Ph.D. student at CMU's Dietrich College and lead author of the geometry study. “He would come up to the screen and wait for me to turn the computer on, and then he’d just sit there for two to three hours just doing all kinds of mathematical tasks.”

The Primate Portal offers open access to data, code and video of primates who are solving cognitive problems, with the goal that students everywhere can study animal minds.

Cantlon has also worked with another study coauthor, Caroline DeLong at the Rochester Institute of Technology, to bring the Primate Portal concept into elementary school classrooms by teaching young children how to code. The students then get to travel to the zoo to see the baboons play the games they have developed for them — an experience the researchers have linked with elevated math and science scores and an uptick in interest of STEM career paths.

The Origins of Human Thought

All of it leads back to a simple question, said Cantlon: “How did we come to think in the way that we think?”

From a 70,000-year-old stone etched with reoccurring parallel lines to a 35,000-year-old mammoth tusk full of 88 notches organized in rows, archaeology tells us that humans have been sensitive to Euclidean geometry for a very long time.

“It’s one of the first things that humans wanted to write down. And those kinds of intuitions feel automatic to us, because we’ve encoded them so deeply,” said Cantlon. “But even thinking about a two-dimensional shape and being able to understand the properties it shares with another object is a really abstract kind of cognition.”

A really abstract kind of cognition shared by monkeys, it turns out.