The Secret Reason Why We Cry

Tears as an honest signal of trustworthiness.

Posted Oct 07, 2019

Crying as an expression of emotion appears to be uniquely human behavior. Other animals may tear up because of irritants in their eyes, but only humans shed tears at times of extreme sadness or joy. There’s no clear answer to the question of why humans cry, but evolutionary psychologists have proposed a couple of explanations.

One possibility is that crying elicits helping behavior from others in times of need. It’s certainly true that we’re emotionally affected by the sight of another person crying in despair. We may even be more motivated to help out if we see tears than otherwise. In other words, tears are a solicitation for altruistic behaviors—that is, doing a good deed for another at a cost to oneself.

Another possibility is that crying is an honest signal of trustworthiness. Proponents support this view by citing two pieces of evidence. First, crying is a behavior largely outside of conscious control. We can easily fake a smile or a frown, but we can’t just shed a tear at will. Second, crying blurs vision, putting the person shedding tears at a disadvantage.

Humans cooperate with each other far more than other animal species. But to facilitate that cooperation, we need to provide others with honest signals of our trustworthiness. And tears bear all the hallmarks of an honest signal, in that they’re hard to fake, and they put the signaler at a disadvantage.

So perhaps we cry to signal that our emotional expressions—whether of sadness or joy—are sincere. In an article recently published in the journal Evolutionary Psychology, New York University psychologist Lawrence Reed and his colleagues described two experiments that pitted these two hypotheses against each other. They did this by creating laboratory scenarios in which altruism and trustworthiness could be separated.

In the first experiment, the researchers had participants engage in what’s known as the "Trust Game." To start, participants were given a sum of money, 10 cents in this case. They were then told that they could keep the money, but if they gave it to another person, called the “trustee,” that amount would be tripled to 30 cents.

The trustee could then either keep all the money for herself, or she could split it evenly with the participant. In other words, if the trustee is honest, you can increase your money by half (15 cents), but if she’s dishonest, you’ll lose everything. This task is commonly used to examine the personal and situational factors that influence people’s willingness to trust another person.

Before making their decision, the participants got to see a brief video of the trustee, who was always portrayed by the same woman actor. However, each participant got to see her in only one of four conditions: neutral expression without tears, neutral expression with tears, sad expression without tears, and sad expression with tears.

If tears signal a need for help, participants should be more likely to hand over their money to a trustee who’s crying, whether her emotional expression was neutral or sad. In contrast, if tears are an honest signal of trustworthiness, the participants should be more likely to give the trustee their money when she cried, regardless of her expression.

The results of the first experiment were ambiguous. When the participants saw the trustee cry, they were willing to trust her with the money around 85 percent of the time, whether she had a neutral or sad expression. However, the participants also trusted her with the money almost 80 percent of the time even when she had a sad expression without crying. In other words, trust was only low when the trustee had a neutral expression with no tears.

Thus, it could be the case in the first experiment that the participants handed over the money because they felt sorry for the trustee, either because she was crying or because she looked sad. However, the hypothesis that tears are an honest sign of trustworthiness cannot be discounted, since, after all, the participants were most likely to give the trustee their money when she was crying.

To address this issue, the researchers conducted a second experiment. This time, they employed what’s known as the "Dictator Game." In this exercise, participants can choose to either keep the money for themselves or else give it to the trustee, who will then keep the cash for herself. If tears signal a need for help that elicits an altruistic response from others, the participant should be more likely to surrender their earnings when they see the trustee cry.

In this second experiment, the researchers found that participants were most likely to give up their earnings when the trustee showed a neutral expression and no tears. Conversely, seeing tears or a sad expression made the participants less likely to engage in an altruistic act. Thus, these data suggest that the purpose of tears is not to elicit help from others.

Comparing the results from these two experiments, Reed and colleagues found that tears elicited trusting behaviors from the participants, but not helping behaviors. Therefore, the researchers concluded that the second hypothesis, namely that tears are an honest signal of trustworthiness, was supported by the data. Furthermore, they found little support for the first hypothesis that tears elicit altruistic acts.

As the researchers point out, there is hardly any research on the causes and consequences of crying. So this particular set of experiments needs to be interpreted as an initial foray into the field and not a definitive study of the phenomenon. Only humans cry, but now researchers are starting to unravel this evolutionary mystery.

Facebook image: Rachaphak/Shutterstock


Reed, L. I., Matari, Y., Wu, M., & Janaswamy, R. (2019). Emotional tears: An honest signal of trustworthiness increasing prosocial behavior? Evolutionary Psychology. Advance online publication.