Yawn. Stretch your arms into the air, close your eyes, and yawn audibly. Feel how it relaxes you. Yawn, yawn, yawn. Yaaaawn. You just yawned, right? The very word makes the action irresistible, somehow.

But are yawns really contagious? In order to find an answer to this question, it is important to first figure out what we’re really asking. Does yawning tend to make people around you yawn? Well, yeah — that’s sort of why we’re here. Does yawning actually compel a subconscious, biological response the way other contagions do? Do we “catch” it the way we catch colds and other infections?  Now we’re talking.

The short answer to this is “no” — people with developmental disorders like autism, for example, appear to be entirely immune to the yawn contagion. Instead, its contagiousness is more closely related to that of laughter and sadness. It is, according to Dr. Michael Campbell of Emory University, an exclusively social phenomenon.  

“Yawns are contagious for the same reason that smiles, frowns and other facial expressions are contagious," he said, speaking to Live Science. "The mechanism that allows someone to reflexively mimic a smile is thought to also allow for reflexive mimicry of yawns."

This implies that, in order to figure out why yawns are contagious, we should think less about its biological significance and more about its social significance. To do this, it is useful to invoke the wisdom of evolutionary psychology — a booming field of science where researchers start with the premise that nature is its own harshest critic. Evolutionary psychologists assume that, if a behavior doesn’t fulfill an important purpose, it will not endure across generations. The yawning contagion clearly did. Why?

One attempt to resolve this social significance of yawning is found in a 2007 study by Drs. Andrew C. Gallup and Gordon G. Gallup Jr. of the State University of New York at Albany. Published in the journal Evolutionary Psychology, the findings show that yawning may be a type of defense mechanism that cools the brain and increases group vigilance. This way, a population prone to yawning develops an evolutionary edge.  

That said, it could also be a type of social byproduct of other forms of interaction. Rather than a trait useful in its own right, yawning may have “piggybacked” on enduring mimicked behavior, such as smiling and crying. "It might be useful to coordinate the level of alertness within the group, but there is no evidence supporting it,” Campbell told reporters. “Or it could be a byproduct of empathy — closely attending to family and friends and [feeling] for them, which would help maintain relationship."

The yawning contagion may remain a mystery. Science, however, is often more interested in the questions themselves rather than answers that may or may not be forthcoming.