The commonly-held belief is that certain facial muscle movements (called expressions) evolved to express certain mental states and prepare the body to react in stereotyped ways to certain situations.
For example, widening the eyes when you're scared might help you take in more information about the scene, while also signalling to the people around you that something dangerous is happening.
"What I decided to do in this paper is remind readers of the evidence that runs contrary to the view that certain emotions are biologically basic, so that people scowl only when they're angry or pout only when they're sad," says Lisa Feldman Barrett of Northeastern University, the author of the new paper.
"When do you ever see somebody pout in sadness? When it's a symbol."
"Like in cartoons or very bad movies. 'People pout when they want to look sad, not necessarily when they actually feel sad.'"
Some scientists have proposed that emotions regulate your physical response to a situation, but Barrett asserts that there is no evidence, for example, that a certain emotion usually produces the same physical changes each time it is experienced.
"There's tremendous variety in what people do and what their bodies and faces do in anger or sadness or in fear."
People do a lot of things when they are angry. Sometimes they yell while sometimes they smile.
Instead of stating that all emotions fall into a few categories, and everyone expresses them the same way, Barrett insists that psychologists should work on understanding how people vary in expressing their emotions.
"There's a lot of evidence that there is no signature for fear or anger or sadness that you could detect in another person. If you want to improve your accuracy in reading emotion in another person, you have to also take the context into account."
Incidentally, the theory that emotional expressions evolved for specific functions is normally attributed to Charles Darwin, in his book The Expression of the Emotions in Man and Animals. But Darwin did not write that emotional expressions are functional.
"If you're going to cite Darwin as evidence that you're right, you'd better cite him correctly," Barrett added.
Darwin thought that emotional expressions like smiles, frowns, and so on -were akin to the vestigial tailbone and occurred even though they are of no use.
The study has been published in Current Directions in Psychological Science.