Facial Expressions and Evolution

Darwin thought that our expressions showing emotion came from animal ancestors, but that is clearly ridiculous, since human facial expressions are extremely diverse and unique, far more so than any animals. Some animals show surprise, fear, and a few other basic emotions, but people often "see" an expression of emotion that is not necessarily there and give it a meaning. When Basement Cat gives me a look that my wife and I cannot fathom, I jokingly refer to it as her "I know what you did" look. Also, I've never seen an animal's expression when it smelled something either pleasant or awful. (I thought of this when I was in a corridor at the workplace and walked into an invisible fog of bad perfume, and made a face about it.)

Human facial expressions are far more diverse than those of animals, and many of them cross cultural boundaries for communication.
The Card Players, Paul Cezanne, 1892
Poker players learn to use a "poker face" where they try to be devoid of expressions so that other players can't tell whether or not someone has a good hand. Skilled players watch for "tells" that involve body language as well as facial expressions and head movements. There are times when I put on a poker face to avoid showing emotion, and sometimes people have wondered if I was angry or depressed. Maybe I was a mite troubled, or not. Sometimes, we give very subtle and quick changes that others may pick up on, even subconsciously. 

The many facial muscles that are used to show emotion often cross cultural boundaries, such as the smile, which requires fewer muscles than anger. Communication with our facial expressions seems to be another gift of our Creator.
Even before they can say a word, newborn babies can “talk” with their faces. In fact, every human being has the ability to communicate in this language, with a range of expressions no other creature can match.

When we think of muscles, we generally think of the big ones in our arms and legs—under our voluntary control—which are attached at both ends to our skeleton and allow body movement. But the skin on our face has over 40 voluntary muscles that, among other things, allow us to move our skin around to create an amazing variety of facial expressions. These facial muscles originate in the skull bones but attach to the skin of the scalp, ears, neck and face. All facial muscles are controlled by the facial nerves that emerge from the skull behind our ears and split into five branches on each side of our head.
To read the rest, click on "Facial Expressions—The Universal Language". Bonuses: look for the description of the "Elvis Muscle", and there's a short video at the end.