Figure 7.

Music as a dual coordination system. Music evolved to be a dual coordination system, using both tonality and metric entrainment to engender integration. Scale structure (tonality) provides “pitch slots” for coordination, while metric structure provides “time slots” for coordination. As shown at the top, music inherited vocal learning from the musilangauge precursor, and achieved scale structure through a digitization of the levels-and-contours pitch system of that stage. Metrical structure is proposed to be a cross-modal system that originated as mutual entrainment of whole-body movement during group dancing. Music is able to co-opt this cross-modal system as its rhythmic mechanism.