Smiling might be universal across humanity but the emotional state and intent of the smile is not. For example, in some cultures, smiling/grinning is a response to embarrassment. When I was travelling in China I asked a old man for directions (in mandarin)...he was so shocked that a foreigner was speaking with him he couldn't speak back. He grinned from ear to ear though.

Also, in primates, smiling is very closely related to baring of teeth. Smiling = 'let's be friends'. Baring teeth = 'come any closer and I'll kill you'. I would not like to make that kind of miscalculation when meeting an alien for the first time....

> For example, in some cultures, smiling/grinning is a response to embarrassment.

I'd have to ask, then, where is that not true? I know that happens in the USA and a friend of mine from Japan also does that.

Everyone smiles, but for slightly different reasons. North Americans often smile to appear polite, which makes the rest of the world think we're weird (cause forced smiles never reach the eyes).

Spontaneous smiles activate the major cheek muscles (pulling the lips up), as well as the muscles just around the eye. Forced smiles only activate the cheek muscles (it's apparently nearly impossible to consciously activate those eye muscles).

There's also questions of degrees of smiling, as in amount of teeth.

It is not impossible, one just needs to actively learn to use the muscles around the eyes to make real-looking smiles. Takes a few years of sporadically applied effort though.

I had a Russian professor (teaching the language, and from the country) in college who mentioned one day in class (I forget how we got onto the subject) that Americans smile a lot more than Russian people, and that it generally seemed false and insincere to her. I've had other Russians confirm this, though they generally tend to be older.