Science is beginning to entertain the idea that human hypocrisy may derive directly from primates. Knowing this does not make it better or worse, but it is worth keeping in mind that the brain arrives already equipped for it.

Facial expressions sit at the very center of social life, and yet scientists still do not fully understand how the brain produces them. For decades, a widely accepted theory has held that what appears on a person’s face largely reflects their emotions—an honest, automatic reading of what they feel. But this does not account for the fact that we routinely modulate our expressions and gestures depending on the situation in which we find ourselves. We have all smiled politely at someone we dislike, or tried not to smile when something suddenly places us in a position of advantage.

To determine what happens in the brain when facial expressions arise, a group of researchers recently turned to rhesus macaques—Old World monkeys whose facial musculature and neuroanatomy closely resemble our own. They recorded neural activity in the laboratory while the animals interacted with one another, with human experimenters, with digital avatars, and with videos of other macaques. The team’s results, recently published in Science, were rather unexpected. All of the monkeys’ expressions—from threatening displays to affiliative gestures—were generated by both the medial and the lateral cortex.

This is striking because, for a long time, these two regions of the frontal lobe were thought to operate independently. The medial cortex was believed to handle spontaneous emotional expressions, while the lateral cortex controlled voluntary ones. It would seem that this distinction was not especially well conceived, as the study shows that all regions participate in the production of all types of expression.