I propose a challenge: To find out how close you really are to your significant other, go out on a date together and yawn—that’s right, yawn. Sure, you’ll risk making your partner think that he or she is boring you, but don’t worry…there’s a method to my madness.

Of course you already know that yawns are “contagious”—when one person yawns, another person who notices the yawn is likely to follow suit—but a new study recently found that the more often and the sooner that someone else copies your yawns, the more emotionally close he or she feels to you.

To find out more about this phenomenon, I called study coauthor Elisabetta Palagi, PhD, a primatologist (yes, we humans are primates) and anthropologist at the Natural History Museum of the University of Pisa in Italy, whose research appeared in December 2011 in the journal PLoS ONE.

UNDERCOVER DETECTIVES

In the study, researchers didn’t tell participants that they were being observed, but sat down near different groups of them in offices, restaurants, waiting rooms and other public spaces to scrutinize their yawns. The researchers acted normally while secretly recording information, so the participants weren’t suspicious. Researchers either knew the participants (and therefore knew their relationships to each other) or were able to get the subjects to reveal that information during conversations later.

When an individual yawned, researchers noted who else in the group “copied” the yawn and the relationship of those people to the original yawner. Researchers also timed how soon after the original yawn others “copied” the yawn. Three minutes was considered to be the maximum amount of time that the yawns could verifiably “catch.” (For example, if Person A yawned and there were, say, three consecutive yawns by three other people within three minutes of Person A’s yawn, then those three people were considered to be “copying” Person A’s yawn, not each other’s.) Each of these group sessions lasted anywhere from 30 minutes to two hours.

The results: In the 480 bouts of yawning analyzed over one year, the researchers found that yawns were most contagious among relatives. For example, they discovered that about 50% of all yawns are contagious between relatives, compared with about 25% of those between friends, about 13% between acquaintances and less than 10% between strangers. Researchers also discovered that people related to the yawner and friends of the yawner “copied” the yawn more quickly—in other words, the contagion spread faster—compared with people who weren’t as emotionally close to the yawner. For instance, relatives of the first yawner who “copied” the yawn did so within just one minute two-thirds of the time. Friends did the same half the time. But most acquaintances of the yawner and those who didn’t know the yawner took as many as two or three minutes to copy a yawn.

WHAT YAWNING REVEALS ABOUT US

You might think that yawning is usually triggered by fatigue—but in fact, said Dr. Palagi, that is true only about half the time. The other half of all yawns, she said, are actually made in response to another yawn.

Why does seeing a yawn make you yawn? From a physiological standpoint, Dr. Palagi said, seeing a yawn activates a complex network of brain regions related to imitation, social behavior and empathy…and from a social standpoint, in those viewing the yawn of someone they care about, these brain regions may become so stimulated that they force a yawn to emerge as a signal—a signal that says, “I understand what you’re going through. I feel what you feel.” In other words, the research suggests that the closer you are to someone, the more likely you are to empathize with him or her—therefore, the more likely you are to copy a yawn quickly.

So, go ahead and take the Valentine’s Day yawn test. If your significant other doesn’t yawn immediately after you do, don’t get too worked up about it—it’s certainly not an infallible measure of how much he or she cares for you, said Dr. Palagi. It might just mean that the two of you have been spending too much time apart lately. Maybe the two of you could benefit from scheduling more quality time together and getting closer—no yawning required.