We think we understand why we are driven to eat, drink, have sex, talk and so forth, based on the uncontroversial adaptive functions of these urges. The drive to engage in music, a compulsion that is arguably just as pervasive in our species, has no such ready explanation. Music was one human behaviour that Charles Darwin was uncertain he could explain, writing in The Descent of Man, and Selection in Relation to Sex: "As neither the enjoyment nor the capacity of producing musical notes are faculties of the least use to man ... they must be ranked amongst the most mysterious with which he is endowed." Music's origins have remained puzzling in the years since, although there is no shortage of speculation on the subject. Some argue that music is merely a side effect of traits that evolved for other functions. Our perceptual and cognitive abilities may have accidentally resulted in a system that finds pleasure and interest in musical stimulation. This idea should perhaps be the null hypothesis, and is by no means implausible. Music's perceptual basis could derive from general-purpose auditory mechanisms, its syntactic components could be co-opted from language, and its effect on our emotions could be driven by the acoustic similarity of music to other sounds of greater biological relevance, such as speech or animal vocalizations.