Ever wondered if someone you're attracted to likes you or not, whether someone is your friend or foe, or whether your employees respect you? There's an easy way to find out... try to make them laugh. If the laughter comes easy, the answer is likely yes. If it doesn't, the answer is likely no.

In my bachelor days, I spent many years slowly learning about the ins and outs of the market. Somewhere along the way, I noticed one fairly consistent dynamic: whenever a woman I recently met would say "You're really funny!" she would always be up for going out with me. In contrast, if I asked someone out who had not laughed at my ever-so-witty remarks, I would often hear about a mysterious boyfriend or busy schedule.

In my first corporate job, I was working on a project team for a few months where I didn't really like my two supervisors all that much. Although I never explicitly told them that, I may have nonetheless communicated my disdain: I didn't laugh at their jokes. To me, they were mostly lame, sometimes offensive. However, the other guys on the project team would always laugh as if the supervisors were highly skilled entertainers. The implications became clear on the day that we all received our performance reviews. While those other guys were smiling at their glowing reviews, I was left wondering whether my subpar appraisal might've been better had I laughed at any of those jokes.

Many years later in grad school (my advisor was Prof. Douglas Kenrick—now, there's a truly funny guy), I transformed these and many related observations into a psychological theory on . I proposed that humor may have evolved as a way to indicate interest in potential and existing relationships with romantic partners, friends, allies, family members, etc. That is, people initiate humor and gauge the reaction in order to test the social waters. And, just as you're more likely to dab your foot into the pool if you're actually contemplating a swim, you are more likely to be interested in some kind of relationship with a person if you initiate any kind of humor towards them. If the other person is also interested, they should be more likely to perceive you as humorous and respond favorably (laugh), even if you're objectively not all that funny. However, if they're really not interested, then they probably won't find humor in what you say, even if it's your best material.

When we meet new people, it may take a while to figure out whether a relationship (of any kind) is desirable. By initiating humor and responding to it, we can indicate the direction of our interest a little at a time. Similarly, for ongoing relationships, people may have a need to monitor how the relationships are going. Humorous exchange among existing partners or friends allows people to indicate whether they are satisfied or aligned with each other. For example, while working on this theory back in 2002, I noticed one day that my romantic partner was no longer at some of the silly little things that I said or did that used to make her laugh. I told her all about the theory but she insisted that her lack of laughter had nothing to do with dissatisfaction—she was just worried about other things. Well, a few months later, the relationship crumbled: we separated and never got back together. It turns out that the time when she started not laughing at my jokes was exactly when she started confiding in others.

Humor may serve many functions, but the "interest indicator" theory says that an important one is to indicate relationship interest, whether among potential or ongoing mates, friends, and allies, or among family members. In this way, a humorous exchange feels good because it indicates that the people who we like also like us. On the flipside, a failed humor attempt can sting not necessarily because our joke is being rejected but because we are being rejected.

My colleagues and I ran three studies to test this theory in the mating domain (Li, Griskevicius, Durante, Jonason, Pasisz, & Aumer, 2009). Take a look for more details or listen here. In the meantime, take notice of who makes you laugh and who you are able to make laugh. Just as importantly, beware of those who aren't laughing.