Why do we even have artists? Do we really need them, from an evolutionary point of view?
Artists should have died off
Who needs artists, anyway?
Most of them, historically, are not very good at the productive stuff, which makes them a burden on society. The thing that they are good at is not very useful for society and all other animals have done well without pictures or stories or music. We don't really need movies or music or dancers or poets to survive, do we?
Not only that, artists are usually a destabilizing influence on society. They keep trying to break rules (usually), they keep living a wild and sordid life (overall), their art keeps pushing boundaries that disturb the careful balance of society (mostly).
It would seem to make sense that a society that succeeded in eliminating its artists would survive better and therefore have an evolutionary edge. Its people would work better and longer, would not dream of better things, and the rules of the society would be less threatened.
Why didn't artists die off and leave our societies more stable?
Art increases people's intelligence
Most stories are good for our intelligence. When small kids listen to stories, they experience in their minds situations they haven't been in and learn how to cope. They listen again and again to the same stories, and imagine what it feels like to be in that situation. The same is true with grownups. Some stories help us prepare for future situations and/or understand past situations better.
Imagination also helps increase people's ability to think, seeing as it breaks old forms and helps imagine new ones. Imagination is a very good surviving tool. The better your imagination, the better your ability to cope with change, to win wars, to advance in society, etc.
Being able to think outside the box promises a more intelligent society, even if the person who first thought outside the box was one of them artist types. Being forced to push back when somebody pushes your boundaries or buttons, magnifies your ability to justify the boundaries, and also helps you move them should the need for it arise. If change becomes necessary, the fact that your boundaries were already in question, makes it easier to change them. An ability to bend under changing circumstances is a mark of intelligence.
But these things don't exist in all pieces of good art.
Art crystallizes ideas and emotions
What every piece of good art does is crystallize ideas and emotions.
The better the art the more precise the expression of emotion. Artists make solid emotions that are fluid and that don't have a name. If you hear a piece of brilliant music and it captures the way you feel precisely, you are then able to look at some of your emotions in a more precise manner. If a painting captures a feeling you never knew you had, now you know you have it. Your emotional intelligence increased somewhat. If a brilliantly constructed building shows you a relationship of the spaces around you that you saw but couldn't place or that brings some enlightenment to a place in your mind you didn't know was there, you are now a slightly wiser person. If a dance tugs at your heart in a place that has no name, if a play makes you feel like you experienced something bigger than yourself, then your world is richer and your ability to handle it has marginally increased.
So. Turns out artists are good for us. Take two a day before each meal and you'll be fine.