But our expressions are less a mirror of what’s going on inside than a signal we’re sending about what we want to happen next. Your best ‘disgusted’ face, for example, might show that you’re not happy with the way the conversation is going – and that you want it to take a different tack.

“It’s the only reason that makes sense for facial expression to have evolved,” says Bridget Waller, an evolutionary psychology professor at the University of Portsmouth. Faces, she says, are always “giving some sort of important and useful information both to the sender… and to the receiver.”

While it may seem sensible, this theory has been a long time coming.

The idea that emotions are fundamental, instinctive and expressed in our faces is deeply ingrained in Western culture. Ancient Greeks placed the ‘passions’ in opposition to reason; in the 17th Century, philosopher René Descartes laid out six basic passions which could interfere with rational thought. Artist Charles Le Brun then connected them to the face, laying out “the anatomically correct and appropriately nuanced facial configuration for each Cartesian passion”, write Crivelli and Fridlund.