Scientists from Yale University have found that monkeys make joint decisions much more “smartly” than previously thought. New research has shown that during cooperation, marmosets literally “read” each other’s gaze and body movements, and their brains gradually accumulate social information before taking action. The results of the study were published in the journal Neuron.

During the experiment, pairs of monkeys had to pull levers at the same time, but the time difference should not exceed one second, and only then would the animals receive a treat.

To complete the task, the marmosets had to carefully watch each other, catching the direction of their gaze, head movements, body position, and signs of readiness for action.

The researchers called this mechanism “social gaze.” In essence, the monkeys were constantly collecting signals from their partner and trying to predict when it would be better to act together. During this time, a part of their brains called the dorsomedial prefrontal cortex—a region associated with social thinking and decision-making—became more active. The scientists watched as the neurons’ activity gradually increased as the joint action approached.

What’s particularly interesting is that the monkeys’ brain used a mechanism that is very similar to the human decision-making process. The researchers compared it to the “accumulation of evidence” model: the brain gradually accumulates information until it comes to the conclusion that the moment for action has arrived. Until now, it was thought that this type of calculation is mainly associated with individual choices, but now it has been found that it also operates in social interactions.

The researchers believe that the results of this study help to better understand the origins of cooperation in primates and humans. According to them, such mechanisms could have played an important role in the evolution of communication, cooperation, and even empathy. In addition, the research could help study conditions associated with impaired social interactions, including autism spectrum disorders.

The scientists note one interesting detail: the better partners know each other, the less they need to actively “read” each other’s signals. Over time, the brain seems to build an internal model of another being’s behavior and begins to almost automatically predict their actions. Perhaps this is how strong social bonds are formed—not only in monkeys, but also in humans.