Monkeys are surprisingly good at geometry

Only a handful of species apart from humans are known to understand geometry. It’s considered so rare among other animals that most scientists have long assumed even our closest non-human primate relatives struggle to grasp the concept of shapes and space. But according to a new study published today in the journal Proceedings of the National Academy of Sciences, some monkeys may not only have a solid handle on geometrical ideas—they cognitively process them in the same way as humans.

“What surprised us wasn’t just that monkeys could do the task. It was that monkeys, children and adults seemed to think about geometric relationships in fundamentally the same way,” Jessica Cantlon, a study co-author, a cognitive neuroscientist at Carnegie Mellon University (CMU), explained in a statement. “That suggests these intuitions are part of the basic architecture of the primate mind.”

Canton and colleagues designed an experiment focusing on olive baboons (Papio anubis) and Rhesus macaques (Macaca mulatta) living at the New York’s Seneca Park Zoo’s Primate Portal, an ongoing project overseen by CMU researchers and the Rochester Institute of Technology. There, primates are allowed to freely interact with a touchscreen offering various customizable cognitive-based tasks. Data, code, and video of those results are then made publicly available as open access information.

In this case, the baboons and macaques were offered fruit for participating in a two-dimensional geometric shape matching game. Cantlon said that although the concept may sound simple, it’s deceptively more difficult because the objects don’t feature particularly distinct attributes across form, size, and color.

“You’d get tripped up, too,” she warned.

The Primate Portal Tests Monkey Math Skills and Teaches Kids to Code thumbnail

To measure the primates’ results, the team then offered the same game to preschoolers, 21 American adults, as well as nearly 80 adults from the Tsimane’ people. The Tsimane’ are an Indigenous subsistence agrarian group living in the tropical lowlands of Bolivia, and do not receive formal education like most other present-day societies. This helped Cantlon’s team to better separate factors like age and culture.

“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,” she explained. “So if we want to understand how children learn geometry, we need to understand what they bring to the table before formal instruction begins.”

Including the Tsimane’ proved crucial. The range stretching from the two primate species to human children and adults from different educational and cultural backgrounds showed a clear spectrum of understanding when it comes to basic geometry. The study results strongly imply that human children are born with evolutionary intuitions around space and shape. Instead of structured geometry education beginning from nothing, the lessons are built on those existing and innate principles.

Some of humanity’s most ancient artifacts support the argument that our species (and our evolutionary relatives) have long grasped Euclidean geometry. Inside the Blombos Cave in South Africa, paleoarchaeologists previously discovered a 70,000-year-old stone engraved with multiple parallel lines, as well as a 40,000-year-old mammoth tusk’s rows of notches in Germany.

“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,” Cantlon said.

However, it now appears that this encoding didn’t begin with us.

“One of the baboons, named Kalamata, was the hardest working monkey that I’ve ever seen,” added study co-author and CMU cognitive scientist Jialin Li. “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.”