Maybe you have a good sob every week, or haven't shed a tear in years. Either way, if you're human, you've shed an emotional tear or two. That makes you unique among the world's species: though other creatures tear up because of physical pain or irritation, we are the only ones whose tears can be triggered by their emotions.
But why do we cry? That question has persisted for centuries (and is the subject of a recent feature article in TIME). Now, scientists are beginning to understand why humans shed tears—and why some don't. Find out how your crying habits compare to those of others by taking the survey below.