The Origin of the Human Smile

A colleague and grad student of mine, Rob, just sent me the following question, slightly edited here:

A student in my intro class asked me a good question the other day to which I had no answer. When did smiling cease to be a threat gesture? I have a couple of ideas. One is that with reduced canines, smiling became a way to say "look, I have small canines, I am not a threat to you." The other is that smiling is based more on a "fear-grin" than a threat. Under this idea, smiling might have been a way of showing deference to others. If everyone shows deference, it would be egalitarian, until the one guy comes along who never smiles. Maybe that's why bosses often don't smile. ... let me know when you have some free time to have lunch. Tuesdays and
Wed's probably work best for me.

Good question, and good ideas as to a possible answer. I have a couple of other ideas to contribute....

(a repost)

Dare I say "It's too bad that smiles don't fossilize..." But really, if we started digging up smiles, that might make palaeoanthropology too weird to contemplate and fewer people would go into the field.

Since primates seem to use facial gestures like smiles and yawns to communicate emotional state and to negotiate social status, a comparative approach is reasonable. However, human emotions have been incorporated into a set of social relations that are very derived so this is difficult.

In The Face: A Natural History, Daniel McNeil refers to a study that shows that while judges are as likely to convict (or not) smiling defendants, the ones who smile get lighter sentences.

Smiling is innate in infants, and has obvious social implications in humans, but the role and nature of the smile ... as far as what the mouth is doing while smiling ... seem to have culturally bound variation.

Have you seen the movie Platoon? For a few years, some time before that movie came out, I had the pleasure of working with a number of Viet Nam vets (doing archaeology and historical research). I heard a number of stories from them over the years, and Platoon, interestingly, seemed to me to be a catalog of horrors experienced by most of the ground troops who spent a fair amount of time in that conflict. One of the events that happens in the movie involves a raid on a village suspected of harboring "Viet Cong" or stashing weapons. The Marines corner a young man and insist that he tell them where the bad guys and/or weapons are hidden. The young man is totally freaked out, but appears to be smiling at the Marines. This enrages one of the Marines, who eventually kills him.

What the Marine missed is that in the culture of that region, there is a facial expression that Westerners will often interpret as as smile, but it is in fact a grimace. The corners of the mouth are turned up and the teeth are showing, but there is nothing happy going on at all. We do see this in Western settings as well, just not as often. My daughter was perplexed a few months back when one of her friends seemed to be smiling while talking about the death of her father a day or two earlier. The girl's emotions were clearly showing, but a negative expression appeared as a smile (at least that is what I think was happening).

The mouth-smile of primates is, in fact, usually a grimace and not a happy thing (as you point out). I think primates do different things to show that they are happy, and smiling may not be on the list.

A hard core evolutionary psychologists might suggest that s smile shows a state of health by showing a complete set of teeth, indicating normal development during childhood and that you have spent a life not making other people mad at you enough to knock out a few teeth.

I'm not sure I like the canine/no canine idea too much because that is a display that operates across broad phylogenetic differences. Consider analogues to this argument with other physical traits. Every time a whale pirouettes in the water it is demonstrating that it does not have those ancient land-mammal legs any more. I don't think the other whales would be impressed. (I admit that might be an extreme example).

But here is what I think is the most important point: An evolutionary theory about smiling has to take into account the whole face (and perhaps more) and not just the lips and teeth. Look at this picture:

You can tell that this person is smiling and you can't see her mouth. The eyes give it away. Meanwhile, you can tell that this person is not smiling:

By the way, the upper photo is a professional model. She is not necessarily happy, but she is really smiling. She is truly smiling because she is looking at something she truly loves (the camera). The ability to do this is what separates the professionals from the rest of us who always look like we are faking it when the person taking the picture with one of those horrid PHS digital cameras takes nine minutes to press the button while we stand there waiting.

Expressions can be important. They can even tell you what a member of another species is thinking, as has been demonstrated over and over again by the insightful LOL cat movement:

As for lunch, Wednesdays are good for me.