You know what they say: when you’re smiling, the whole world smiles with you. As it turns out, there’s a reason for that. A study published today in the journal Trends in Cognitive Sciences shows that mirroring other people’s facial expressions helps us connect. 

Scientists have known for some time now that our facial expressions can actually change our moods. A 2012 study found that people who held chopsticks in their mouths lengthwise, forcing their faces into fake smiles, felt happier and less stressed than people who maintained neutral expressions. 

We have a lot to gain from connecting with and understanding other humans; at times, that can mean the difference between life and death. As a result, we have evolved mechanisms that make those connections easier.

“Most people are face perception experts,” the authors write. “Faces, especially those expressing emotion, automatically capture our attention, and we extract the emotional meaning of those faces in a matter of a few hundred milliseconds, even subconsciously. Expressions of intense emotion, such as a wide-eyed expression of fear or a toothy grin, may have evolved to be highly distinguishable signals, easily recognizable even from a distance.” 

This study found that humans subconsciously “try on” each other’s expressions in order to understand how others are feeling. The authors reviewed 15 recent journal articles on facial expression mimicking and the role of muscle movements in emotion. There, they found evidence for what they call the sensorimotor simulation model of emotion perception. In plain English, they’re suggesting that we move our facial muscles to mimic the face in front of us, and that this movement triggers the memory of associated emotions, which triggers real emotion in the moment. 

An example: You’re used to frowning when we feel sad or angry. If you’re sitting in a coffee shop with your friend and she is frowning, even a little bit, you might frown too, without even realizing it. As your brain recognizes the frown on your face, it calls up examples of frowning in your own life, and the feelings that went along with them. You begin to feel just a little bummed. Because this is how your friend is feeling, it helps you connect and relate to her. Voila: social success.

The authors note that this skill is dependent on having a clear view of someone else’s face and being able to replicate their expression. Many people with autism avoid making eye contact, which may contribute to their difficulty recognizing others’ emotions. People who have had strokes or experienced Bell’s palsy may have trouble moving their facial muscles, which limits how much they can mimic the faces in front of them. People who were born with facial paralysis, on the other hand, have often developed other ways to tap into that same empathy.

For their next project, the researchers intend to study how humans perceive and identify other people’s facial expressions.