Expert: John Locke - 8/25/2010

Question
Hello!
Why do we cry when we're sad or sometimes when we're happy?

Answer
Thanks for using AllExperts. Let's define some terms here first: crying, as we're talking about, refers to the shedding of tears in response to emotions without irritation of the eyes. Humans can shed tears in response to irritation of the eyes, of course, as can most other animals, but we are thought to be the only animal that actually cries. The explanations for crying at this point are incomplete, but they range across the spectrum.

The earliest theories suggested that tears were shed in response to pain--situations that were both very sad and very happy could produce the emotional pain required for crying. This idea and others like it suggest that crying is a primal phenomenon related to basic feelings like pain, hunger, thirst, fear, etc.

More recent theories have suggested an evolutionary reason for the development of crying. For example, Oren Hasson, an evolutionary biologist at Tel Aviv University in Israel, has proposed that crying serves as a signal for helplessness or lowered defenses, indicating a need for assistance or reassurance (see http://www.livescience.com/culture/080828-why-we-cry.html). Alternatively, a biochemical explanation has been suggested. Crying may reduce high levels of adrenocorticotropic hormones, which are released in response to stress; this would serve as a kind of check on the amount of stress hormones that could be released. You are likely familiar with the feeling of relief one experiences after crying--that is the mechanism suggested here.

It has also been suggested that crying is fundamentally a reflection of helplessness. That is, we cry when we find ourselves in situations that are beyond our control, either happy or sad (see Miceli, M., & Castelfranchi, C. (2003). Crying: discussing its basic reasons and uses. New Ideas in Psychology, 21(3), 247-273.)

In short,  there is no ultimate answer to this question, but the trend seems to be that crying is recognized as serving some evolutionary purpose and has persisted for that reason. You may wish to read some additional perspectives here:
http://www.npr.org/templates/story/story.php?storyId=129329054

Good luck.