"Crying is a highly evolved behavior," said researcher Oren Hasson, an evolutionary biologist at Tel Aviv University in Israel. "My analysis suggests that by blurring vision, tears lower defenses and reliably function as signals of submission, a cry for help, and even in a mutual display of attachment and as a group display of cohesion."
Crying as a social behavior? What do you think? Link -via Digg
Some people cry when happy , some when sad.Some people cries when they display emotion for others.Some times tears comes out when some obstacle is in eye.