Michael Trimble, a behavioral neurologist with the unusual distinction of being one of the world’s leading experts on crying, was about to be interviewed on a BBC radio show when an assistant asked him a strange question: How come some people don’t cry at all?
The staffer went on to explain that a colleague of hers insisted he never cries. She’d even taken him to see Les Misérables, certain it would jerk a tear or two, but his eyes stayed dry. Trimble was stumped. He and the handful of other scientists who study human crying tend to focus their research on wet eyes, not dry ones, so before the broadcast began, he set up an email address—email@example.com—and on the air asked listeners who never cry to contact him. Within a few hours, Trimble had received hundreds of messages.
“We don’t know anything about people who don’t cry,” Trimble says now. In fact, there’s also a lot scientists don’t know—or can’t agree on—about people who do cry. Charles Darwin once declared emotional tears “purposeless,” and nearly 150 years later, emotional crying remains one of the human body’s more confounding mysteries. Though some other species shed tears reflexively as a result of pain or irritation, humans are the only creatures whose tears can be triggered by their feelings. In babies, tears have the obvious and crucial role of soliciting attention and care from adults. But what about in grownups? That’s less clear. It’s obvious that strong emotions trigger them, but why?
There’s a surprising dearth of hard facts about so fundamental a human experience. Scientific doubt that crying has any real benefit beyond the physiological—tears lubricate the eyes—has persisted for centuries. Beyond that, researchers have generally focused their attention more on emotions than on physiological processes that can appear to be their by-products: “Scientists are not interested in the butterflies in our stomach, but in love,” writes Ad Vingerhoets, a professor at Tilburg University in the Netherlands and the world’s foremost expert on crying, in his 2013 book, Why Only Humans Weep.
But crying is more than a symptom of sadness, as Vingerhoets and others are showing. It’s triggered by a range of feelings—from empathy and surprise to anger and grief—and unlike those butterflies that flap around invisibly when we’re in love, tears are a signal that others can see. That insight is central to the newest thinking about the science of crying.
Darwin wasn’t the only one with strong opinions about why humans cry. By some calculations, people have been speculating about where tears come from and why humans shed them since about 1,500 B.C. For centuries, people thought tears originated in the heart; the Old Testament describes tears as the by-product of when the heart’s material weakens and turns into water, says Vingerhoets. Later, in Hippocrates’ time, it was thought that the mind was the trigger for tears. A prevailing theory in the 1600s held that emotions—especially love—heated the heart, which generated water vapor in order to cool itself down. The heart vapor would then rise to the head, condense near the eyes and escape as tears.
Finally, in 1662, a Danish scientist named Niels Stensen discovered that the lacrimal gland was the proper origin point of tears. That’s when scientists began to unpack what possible evolutionary benefit could be conferred by fluid that springs from the eye. Stensen’s theory: Tears were simply a way to keep the eye moist.