Making or listening to music is pan-cultural, nearly universal, and highly valued. Musical behaviours probably appeared between 500,000 and 60,000 years ago. The more recent date captures the era when Homo sapiens spread globally from Africa. The older date corresponds with a time when song might have produced individual or social benefits and the physiological and cognitive conditions for its production were present (in our predecessor, Homo heidelbergensis). Music is so multifunctional, however, that it is not clear if it was an evolutionary adaptation (as opposed to a by-product or non-biological technology) or, if so, what it was an adaptation for. This chapter examines these issues with a particular focus on questions of musicality, fitness, language, and sound processing.