Mark Van Vugt Ph.D.

Naturally Selected

Why We (and Only We) Cry

Three theories, one of them plausible.

Posted May 12, 2013

aastock/Shutterstock
Source: aastock/Shutterstock

It was a highly emotional moment. In the film Life of Pi, the main character had finally reached shore after a long ordeal at sea. So tired that he collapsed on the beach, he could only watch as his traveling companion, the Bengal tiger he called "Richard Parker," disappeared into the jungle—without once looking back at Pi, his savior.

I was surprised to find tears welling up in the eyes of my young son as we watched the scene. I wondered, why do humans shed tears of sorrow, joy, sadness or happiness? What is the ultimate explanation for the tears we shed when we experience something emotional? Are other animals capable of crying, too? And if not, why did we become the tearful animal?

According to researchers, crying is something humans share with other animals, notably the nonhuman primates. The infants of these species produce crying sounds when they experience something unpleasant, for example. But there are two main differences between us and them: Among humans, not just children but adults cry as well. And perhaps most significantly, when humans weep they actually produce tears. No other known animal produces tears in response to something unpleasant.

So why are we tearful?

The scientific debate about the origin of weeping goes back some time. Charles Darwin considered human crying to be quite insignificant: "We must look at weeping as an incidental result, as purposeless as the secretion of tears from a blow outside the eye," he wrote in 1872.

Yet in the past century or so a dozen theories have been proposed for why we cry, some quite imaginative. Let me share a few, from the ridiculous to the sublime:

  • One theory has to do with our evolutionary past as animals living near coastlines. The “aquatic ape” theory proposes that many of our unique adaptations, including why we are keen swimmers—unlike other primate—is because we evolved near the sea and needed to forage in the ocean. So why do we cry? The tears we produce are basically responses to living in a saline environment. (Think of the tears you produce when seawater gets into your eyes.)
     
  • A second, and fairly ridiculous, explanation is that when our ancestors started to build campfires and the smoke got in their eyes, they started to produce tears. Because fires were used in death rituals we came to associate—in some peculiar way—our tears with negative life-events and that is why we still weep when we watch a sad movie.
     
  • A third, and somewhat more plausible, set of theories for why we cry is that it has a signaling function. Weeping signals that we are defenseless and will not put up a fight when someone wants to harm us. As an extension of this, crying is perhaps a signal to others that we need their help in fighting off an aggressor. (Other social animals use cry vocalizations for this purpose.) When we cry we convey the impression that we are innocent and weak—like children—and need the protection of others.

    But we could cry for help without shedding any tears, couldn't we? Here is an interesting twist: Psychologist Ad Vingerhoets, a crying specialist at Tilburg University in the Netherlands, proposes that alarm cries can be dangerous in an environment teeming with predators, because it indicates your location. Better to sit quietly. Yet how do you let others know that you are in distress? By showing them the tears in your eyes.

    Is there any evidence for this cry-to-get-social-support hypothesis? First, children shed many more tears than adults do, which is what you'd expect if crying is really about wanting protection. Women also cry more—about four times more—than men; again, not surprising since women tend to be physically weaker and potentially more in need of defense. Finally, there is evidence that when we watch a sad movie in the presence of others, we produce many more tears than when we watch it by ourselves.

So, whenever we see someone being tearful in our presence, our automatic response is to offer support. That’s exactly what I did when I saw the tears in the eyes of my son after Richard Parker left Pi. And that is precisely why tigers do not weep.

Vingerhoets, A. (2013). Why Only Humans Weep: Unravelling the mysteries of the tears. Oxford University Press.

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