When Oren Hasson of the zoology department at Tel Aviv University sees a man or woman crying, he asks himself: What is the evolutionary benefit of crying?

Hasson does couples counseling, but is also an evolutionary psychologist, a field that looks at emotional and social phenomena through Charles Darwin's ideas about natural selection. "Our point of departure is the assumption that human beings have undergone an evolutionary process like all other creatures," Hasson says, adding that "they evolved in a manner in which more beneficial characteristics usually were more successful. That prompts us to ask why human behavior is the way it is. What advantage does it provide from an evolutionary standpoint?"

In an article in a recent issue of "Evolutionary Psychology," Hasson argues that crying enables human beings to create a semblance of helplessness while under attack and to convey a credible message of defenselessness. The Israeli zoologist explains that this state of being is created because tears obscure vision and prevent a person from fighting while he or she is crying. Tears prevent someone who is crying, Hasson contends, from effectively acting aggressively and sends the signal that someone who is crying has lowered his or her defenses.

Humans appear to be the only creatures that shed tears as an emotional reaction. Other animals excrete tears to clean their eyes following an injury or irritation from dust, but only human beings cry in social situations as an expression of sadness or excitement. Hasson says that in a setting in which someone is threatened, a crying person unconsciously increases survival prospects, because an attacker understands that someone who is crying is defenseless and there is no reason to continue to attack. In addition, he says, tears send a message of distress to potential allies in the vicinity and to those who are the enemies of the attacker.

Hasson adds that through crying, we are also capable of showing empathy and mutual emotion, creating a social connection and mutual trust. "We are presenting a kind of social display, expressing defenselessness. We lower everyone's defenses. In such a circumstance, the social connection is made stronger, because we are showing that we trust in one another."