So what evolved pleasure buttons does music press? One possibility considered by Pinker includes language, which shares with music the unusual property of being rule-based and recursive and with the power to take a limited stock of units (words of morphemes for language and notes for music) and combining them into a potentially infinite number of structured sequences. However, music gives pleasure through its sound, and language usually doesn't -we typically enjoy it due to what is said, not what it sounds like (On the other hand, there's a pleasure to singing, which has combined the best of music and language...).
But other scholars have proposed music as an adaptation, making the further claim that it exists because it was somehow reproductively advantageous to our ancestors (though the fact that it gives pleasure is not denied). Daniel Levitin, a prominent psychologist who supports this theory points to the idea that synchronous song and dance evolved as social adaptations, helping to establish community and aiding in certain forms of communication. He stresses the importance of music's role in movement, which backs up the theory that the genes of those who created and enjoyed music were able to outcompete the genes of those who couldn't.
Most languages have just one word for both singing and dancing -they aren't exclusive (much to the chagrin of Merce Cunningham, I'm sure). When people listen to music while sitting perfectly still, parts of the motor cortex and cerebellum -areas of the brain that control moving the body's ability to move around- are active. This is why we so often rock and sway to music, an impulse that can be somewhat irresistible, especially to small children. Thus, a theory of music that neglected its relation to movement would be a misstep.
Regarding natural selection, studies have produced evidence that if you move in synchrony with other people, you tend to liked them more, feel more connected to them, have a tendency to be more generous to them. In short, song and dance are the ultimate team-building exercises. This can very well explain the emotional rush that people get from going to a concert or being at a rave. This effect of music may explain why religion is so connected to dancing and music. It has the ability to establish, affirm and maintain a sense of community and solidarity.
All this considered, the potential evolutionary pattern would be that those individuals that could create and enjoy music hung out together, formed communities and cared for one another more easily and more often than those who couldn't. Consequently, the music lovers were more likely to prosper and reproduce. Suddenly, "survival of the fittest" becomes "survival of the musically-inclined."