Why are facial expressions internationally understood?

A smile is a smile in every country, and a laugh is a laugh in every country. A furrowed brow and tight lips is pretty well understood in any country... why are these all basically understood no matter what language is being spoken? Even across different species, we can tell dog emotions by posture and response... I suppose an exception might be fish, but most mammals we can understand basic body posture and emotion. Why?Why are facial expressions internationally understood?
Humans are born with at least 6 different facial expressions that are universally recognizable. These are anger, fear, disgust, happiness, surprise, sadness. Researchers also indicate that 'contempt' may be a possible 7th emotion that appear from birth.





There are many other facial expressions that we recognize too, but these seem to be the ones that appear across all cultures. Perhaps the reason we are so good at interpreting facial expressions is because the basic ones, at least, are ingrained in our genetic coding. Are we good at reading the signals of other animals? I guess so, for the most part - most people can tell if a dog or horse is about to play with them or about to attack them. Perhaps our knowledge of human expressions is extrapolated to other species to a certain extent, allowing us to visually determine the mood of other creatures.Why are facial expressions internationally understood?
E-dot is right.. but I don't really agree with the fact that we understand facial expressions no matter from what culture.. try to watch a chinese or japanese movie.. to me it's even a bit scary not to be able to ';read'; the body language.. to me it seems there sometimes is some sort of a conflict between the facial expression and the emotion conveyed by the (translated) text.. like people looking angry while making a joke, or being very upset while still having a smile on their face..
because we were all taught them when we were young children, so everyone understands them. It is a way we have of communicating with anyone, and a lot of other animals change the way they are looking to signify their emotions, so it must be partly natural to do these things to portray our emotions.
Because most non-verbal communication is universal.