It is firmly grounded in evolutionary development. It's something that Mother Nature provides to help us get along with each other. People can go anywhere and understand these signals, even if they don't know the spoken language. In fact, early courtship is almost entirely made up of nonverbal actions. Men and women unconsciously shrug their shoulders when they find each other attractive.
Early courtship is filled with shy, juvenile, awkward behavior between the man and the woman.
A woman attracted to a man will tilt her head down and to the side, then look in his direction in a coy or coquettish way. A man at a party or at a bar will stake out his territory by putting cigarettes or cash in front of him, t o show females his status relative to other men. A The simplest gesture is simply to turn her body away from him. It is really one of the kindest yet most effective ways to dampen someone's ardor. And men can use it, too.