Babies smile, laugh and cry without being taught. It seems likely that these reactions are inborn and universal.

The hardest part is to track down actual pictures, information, and footage of those who were raised from infancy by animals. I have this vague idea that, without reinforcement from human faces around them, the muscles for smiling will atrophy.

Blind people naturally smile and deaf people know how to laugh, so it's most likely that these are inherent behaviors, not learned.

Gorillas laugh, they probably didn’t learn that from humans. However some facial expressions are learned. In India the way they move their heads when talking is almost a language in itself. These head movements can vary region to region.

It's a mixture I think. There's a tribe which Malcolm gladwell talked about in his book talking to strangers which expressed themselves very differently facially to most in the west.

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Paul Ekman is a psychologist famous for his research on body language/nonverbal communication. He found that there are at least several "universal" emotions and corresponding facial expressions, like anger, sadness, joy, disgust, etc. However, there are thousands of expressions our facial muscles can produce, and it's probable that we learn at least a few of them from our environments and cultures.

yup my baby laughs when having fun but also laughs like a mad man when we laugh, i think its both natural and copy mechanics..

It's mostly genetic. Body language and facial expressions are largely programmed into our DNA and we are born with the knowledge of how to perform them and interpret them. This is unlike verbal language, which is 100% learned.

Have you ever noticed that no matter who the person is on this Earth, whether they be Chinese, African, Native American, European, etc, you can kind of tell if they are happy or sad from a picture or drawing without ever needing to learn anything about their language? This is pretty remarkable. We have a mechanism of communication amongst humans that is universal and belongs to us as a species.

Dogs and other social mammals also have body language cues they use to communicate with one another. You can look up a handbook of all the various dog body language meanings. Tail wagging indicates they are happy or anticipatory, raised teeth and ears back indicates aggression, etc.

Facts.

Came here to mention Ekman. I do CG facial animation for a living, and his work is one of the bibles of the craft. As a side effect, you learn too much about facial features and expressions, and you can read people through micro-expressions and subconscious communications which is a double edged sword. It's pretty dumbed down, but the show "Lie to Me" shows a lot of this.