United States President Barack Obama celebrated his November 2012 victory with a mix of cool eloquence and raw emotion rarely seen in public leaders. The emotion culminated in a teary moment during his speech thanking campaign workers.

Underneath the obvious reasons for celebration lay an ancient mechanism of stress release and interpersonal bonding found in tear production. Contrary to Western stereotypes about crying and weakness, Obama shared something with his audience that has served human needs throughout history.

What is the science behind tears? What is their purpose? Let’s find out…

The Science of Tears

While people feel a profound difference between happiness and sadness, the body often doesn’t make a distinction. Intense situations of any sort can provoke overwhelming reactions. Whether the trigger is a political victory or a crisis, the body produces more stress hormones as part of the preparation for the fight-or-flight response.

Tears act as a safety valve by releasing excess stress hormones such as cortisol. If left unchecked, chronic elevated levels of these hormones can cause physical ailments and play havoc with mood. As stress often precedes a good cry, the sense of calm often felt afterward is at least in part due to hormonal release.

Tears of Victory

The grueling presidential campaign meant months of high stress on top of existing pressures. Once the election results were clear, everyone involved likely felt a great sense of relief that the process was over. Biologically, both winners and losers had elevated levels of stress hormones that needed release. When President Obama gave his post-victory speech to his campaign staff, his body was primed for a heartfelt tear or two. The expression of emotion benefited his supporters as well by boosting a sense of bonding and attachment.

President Obama’s tears were spontaneous, and their genuineness moved his audience. Tears usually signal deep emotion and communicate that a person’s response to a situation is authentic. Nonverbal signs of honesty can be critical in many social situations. In fact, tear production may have evolved partly for this reason.

Raw Emotion Builds Unity

Studies in emotion research suggest that crying often signals vulnerability. By blurring vision, tears lessen a person’s ability to behave aggressively. According to Dr. Oren Hasson, an evolutionary psychologist at Tel Aviv University, crying signals submission to an attacker. It also promotes feelings of sympathy or unity in associates. By letting your guard down through tears, you tell your supporters that you trust and identify with them. Any political strategist can appreciate the value of this dynamic.

Why Fake Tears Don’t Work

Scientists have discovered that the chemical composition of emotional tears differs from those caused by external stimuli such as slicing onions. Emotional tears contain higher levels of certain stress hormones such as adrenocorticotropic hormone, prolactin and the painkiller leucine enkephalin. Adrenocorticotropic hormone and prolactin levels rise with stress. Emotional tears also contain more manganese than those from irritants, and manganese helps regulate mood. Chronically depressed people often have high levels of manganese in their systems.

A good cry from either happy or sad events releases high amounts of stress hormones, protein and manganese. Thanks to these chemicals leaving your body, you often feel relieved and relaxed. Crocodile tears don’t have the biochemical or psychic weight of deep emotion behind them, and an audience can usually tell.

Although President Obama did not plan his emotional display as a tribute to evolution, its effects were true to scientific prediction. His vulnerability sparked a different kind of attention. Much of the audience seemed to respond with sympathy and a sense that this world leader was more like them than perhaps thought. Such social mediation is exactly what tears were designed to do.

The Science of Tears