What was the role of music in the evolutionary history of human beings? We address this question from the point of view that musicality can be defined as a cognitive trait. Although it has been argued that we will never know how cognitive traits evolved (Lewontin, 1998), we argue that we may know the evolution of music by investigating the fundamental cognitive mechanisms of musicality, for example, relative pitch, tonal encoding of pitch, and beat induction. In addition, we show that (...) a nomological network of evidence (Schmitt & Pilcher, 2004) can be built around the hypothesis that musicality is a cognitive adaptation. Within this network, different modes of evidence are gathered to support a specific evolutionary hypothesis. We show that the combination of psychological, medical, physiological, genetic, phylogenetic, hunter–gatherer, and cross-cultural evidence indicates that musicality is a cognitive adaptation. (shrink)