system
Given the following post, respond as if you're commenting on Reddit:
human
The evolution of the smile - it seems incredibly unlikely?

I have a modest understanding of biology, so please be patient. 

How did a facial expression like a smile come into being? I would imagine the ability to manipulate the face would rely upon several genetic mutations. And once they happened, their ability to advantage an organism would depend upon another human in close proximity - at the same time - randomly developing the cognitive capability to interpret such a gesture. 

Doesn't this all seem tremendously unlikely?
gpt
To answer the actual question: No, not really. 

First, the question generally misunderstands evolution, in that evolutionary changes are not "random". The cognitive capacity to visually interpret the actions of others (such as a "smile") in the environment is not a randomly selected for mutation but, rather, a series of systematic changes in neural architecture (e.g., development of a complex visual system) combined with the most simple of associative learning (i.e., thing X leads to thing Y). Such changes would be critically important for surviving in any complex environment, and, so, can be observed in many organisms you'd think are relatively simple.  

And, of course, the ability to manipulate the structure of the face is important for doing things like eating, breathing, and plenty of other behaviors other than smiling. 

Regarding the smile specifically, plenty of animals make gestures like smiles that are very different (in human meaning) than smiles. For example, dogs and monkeys will curl their lips and bear their teeth, and neither are doing it because they are trying to express joy or friendship - both are warning to GTFO. 

In any event, the evolution of facial gestures seems tremendously likely.

Interestingly, the perception and recognition of facial gestures is very different across different populations. For example, Asian cultures rely much more heavily on the eyes than Western cultures. There has been some interesting recent psychological work on this topic by Phillipe Schyns and his collaborators.