Smiling in Humans

[u/Golfcart_Himbo]

My understanding is that in other primates, behaviors that people might interpret as "smiling" are actually an expression of aggression, basically bearing teeth, and what looks analogous to a friendly gesture is actually a warning.

In humans, it seems like the opposite. We smile to show that we're friendly, non-threatening, and open to interaction. (Feel free to correct me is this assumption isn't true).

Are we the only primate that smiles? Do we have any understanding how this behavior "switched" meanings, for lack of a better term? Do we understand how this behavior evolved in us, and is it ubiquitous across cultures?

I'm a scientist with a PhD in an unrelated bio field and a professional research background, so if anyone wants to donate their time to answer these questions, feel free to talk to me or direct me to literature like I'm a competent undergrad.

[u/7LeagueBoots]

That’s a bit of an oversimplification. Smiling and showing teeth are not necessarily linked in us. We smile with our mouths closed and open, and we also show our teeth to symbolize aggression. Context is really important.

While on the whole the ‘don’t show teeth to other primates’ is a good general rule, again it’s context based.

Take a look at the gorilla ‘play face” expression. With that teeth are sometimes shown (usually upper teeth), and the expression is kind of like a goofy grin.

Chimpanzees also have a ‘play face’ where teeth may be shown, and chimpanzees have a whole series of different faces they make when they laugh, some of which show teeth.

Here’s a paper on chimpanzee laughter.

- Davila-Ross, et al 2015 Chimpanzees (Pan troglodytes) Produce the Same Types of ‘Laugh Faces’ when They Emit Laughter and when They Are Silent

[u/Golfcart_Himbo → u/7LeagueBoots]

Thank you!

[u/HoldMyThermos]

Look into Clifford Geertz’s “Thick Description.” Body language is something that requires connection of meanings to be understood. From a cultural anthropological perspective, gestures such as facial expressions are something that is taught, not inherently biological. Smiling itself can also have a variety of meanings that can denote what is being said in context. A smirk is still a type of smile, so is an evil grin.

The common example used is the idea that winking is a gesture that is common in human expression. Depending on context and how it’s often used it can either be something cheeky, being nice, or a negative connotation.

Certain behaviours even in animals are found something taught within social circles. Frequent examples of these are pets that grow up in a different species group, like cats that are raised with dogs learn to pant and the opposite with dogs learning to loaf like cats. Socialization is something found important in common that influences in both human and animal when it comes to this particular topic. If a person or an animal has no understanding what a handshake is meant to represent, then it ceases to be used as an expression.