In Darwinian evolution, a living population evolves when it is exposed to the selection pressures of a new biological medium. Analogously, in my chromatic evolution a chord "evolves" when it is exposed to a new chromatic medium, forcing it to adapt and harmonically modify its pitch content. This is a process by which a diatonic, consonant chord is progressively transformed into a chromatic substitute, over a span of several similar works, without losing or modifying the chord’s resolution tendencies, harmonic function, or formal location. From a Schenkerian perspective—and using Felix Mendelssohn’s Songs without Words as my corpus study—I will demonstrate how the pre-recapitulatory dominant (the root-position dominant that conventionally precedes the recapitulation) progressively evolves into a highly chromatic substitute: the dominant of the mediant.