Monkeys Can Do math: A New Clue on Evolutionary Pattern in Primates' Brain

Author:  Phuongmai Truong
Institution:  UC Berkeley
Date:  February 2010

Mathematics has long been an advance branch of knowledge, even for humans, but recent research shows that rhesus monkeys can learn and apply basic mathematical concepts, such as the Greater-Than or Less-Than rules. Results from this study, done by researchers at the Institute of Neurobiology at University of Tubingen in Germany, was published in the online January 18 issue of Proceedings of the National Academy of Sciences.

Prior studies have shown that many animals, including certain species of fish, amphibians, and honeybees, have a sense of numbers. Evidence of the animals' counting abilities is particularly overwhelming for birds and monkeys. To push the subject further, German researchers Sylvia Bongard and Andreas Nieder focused on animals with higher degrees of brain structuring, such as rhesus monkeys. They wanted to see whether these primates could apply mathematical rules flexibly, a skill that was primarily associated only with humans.

Two rhesus monkeys were presented with groups of both ordered and random dots. These dots were shown in unrepeated combinations to ensure that the monkeys could not have simply memorized the pattern. In the test, the monkeys were instructed to raise or lower a lever to indicate whether each amount of dots shown was greater-than or less-than the amount on a fixed displayed image. The result was that they could apply the rules regardless of dot sizes and densities. In addition, the average number of correct responses for both monkeys was significantly higher than what would have risen from mere random chance. This indicated that the primates understood the mathematical rule and did not choose the answers through guesswork. In addition, the researchers investigated further by looking at the activity of randomly selected neurons in the lateral prefrontal cortexes of the monkeys. These regions of the brain have been found to contain high levels of activity in humans performing arithmetic. Results show that the majority of these neurons in the monkeys were indeed activated during the process of mathematical application.

This study provides further evidence for the activity of network models, which use specific "rule-coding" units to control the information flow between input, memory, and output layers of brain processing. Researchers now hypothesize that this kind of neuron wiring in monkeys was "adopted in the course of primate evolution for syntactic processing of numbers in formalized mathematical systems." In other words, the history of abstract math possibly dated further back than that of humankind. The finding is an early step in probing the evolutionary path to understand more about our own intricate psychology.

Author: Phuongmai Truong

Reviewed by: Brittany Raffa and Yangguang Ou

Published by: Yangguang Ou