Dunbar argues that music evolved, at least in part, as a way of strengthening societal bonds. As a 2010 study of preschoolers found, people who sing or move in rhythmic unison tend to work together more cooperatively afterwards. This explains the presence of music in church services and military ceremonies.
Dunbar and his colleagues argue that their results “at least provide prima facie evidence that music generates the kind of endorphin ‘highs’” that can trigger cooperation—the sort of behavior that was essential for human society to evolve.
Other explanations for the origins of music have been offered, including the notion that it grew out of either courtship rituals or the need to sooth infants. These ideas aren’t mutually exclusive, of course. When and why so many of us evolved into passive listeners is another question.
It would be interesting to experiment on people listening to music not through headphones, or as background sounds in a store, but rather in a concert hall, sitting in rapt concentration with hundreds of other like-minded fans. Could that sort of physically passive but focused attention on music produce the same physiological effect that the players experience? Further research awaits.