Only a handful of species other than humans are known to understand geometry. It is considered so rare among other animals that most scientists have long assumed that even our closest non-human primate relatives struggle to understand the concept of shapes and space. But according to a new study published today in the journal Proceedings of the National Academy of SciencesIt is possible that some monkeys not only have a strong command of geometric ideas, but also process them cognitively in the same way as humans.

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

Canton and his colleagues designed an experiment focusing on olive baboons (papio anubis) and rhesus macaques (mulatto macaca) that lives in the Primate Portal at New York’s Seneca Park Zoo, an ongoing project overseen by researchers at CMU and the Rochester Institute of Technology. There, the primates are allowed to freely interact with a touch screen that offers various customizable cognitive tasks. The data, code and video of those results are made available to the public as open access information.

In this case, baboons and macaques were offered fruit for participating in a matching game of two-dimensional geometric shapes. Cantlon said that although the concept may seem simple, it is deceptively more difficult because the objects do not exhibit particularly distinct attributes in shape, size and color.

“You would trip yourself up too,” he warned.

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To measure the primates’ results, the team offered the same game to preschool children, 21 American adults, and nearly 80 adults from the Tsimane’ people. The Tsimane’ are an indigenous subsistence agrarian group that lives in the tropical lowlands of Bolivia and do not receive formal education like most societies today. This helped Cantlon’s team better separate factors such as age and culture.

“Sometimes when you try to study something in children, it can be difficult to tease out whether their ability is due to development or something learned through education or experience,” he 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 from the two primate species to human children and adults from different educational and cultural backgrounds showed a clear spectrum of understanding when it came to basic geometry. The study’s results strongly imply that human children are born with evolutionary intuitions about space and form. Instead of a structured geometry education that starts from scratch, lessons are based on those existing, innate principles.

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

“It’s one of the first things that humans wanted to write. And those kinds of intuitions seem automatic to us, because we have encoded them very deeply,” Cantlon said.

However, it now appears that this coding did not start with us.

“One of the baboons, named Kalamata, was the hardest-working monkey I’ve ever seen,” added study co-author and CMU cognitive scientist Jialin Li. “He would walk up to the screen and wait for the computer to turn on, and then he would sit there for two or three hours doing all kinds of math tasks.”

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