Most contemporary research in sexual selection assumes that sexual display traits are honest indicators of mate quality or provide mate choice efficiency. I propose that these adaptive mate choice mechanisms are insufficient to explain the complexity and diversity of sexual ornaments in the natural world. I expand upon Darwin‘s original view of mate choice as a mechanism of aesthetic evolution, which requires sensory perception, sensory/cognitive evaluation, and choice. As Darwin hypothesized, aesthetic evolution places the explanation of the evolution of individual subjective preferences at the center of scientific inquiry. A fundamental feature of aesthetic evolution is the coevolution of ornament and the evaluations of them. In this context, beauty can be defined as the subjective experience of coevolved attraction. Aesthetic evolutionary process occurs in many contexts including mate choice, pollination, frugivory, aposematism, mimicry, and offspring ornaments. In mate choice, the fully aesthetic Fisherian mechanism of trait-preference coevolution, as modeled by Lande-Kirkpatrick, is the appropriate null model. The LK null model must be must be rejected before adaptive mate choice explanations can be accepted. Aesthetic coevolution is not limited to non-human animals. Rather, the intrinsically coevolutionary dynamics found in many natural systems also characterize the process of aesthetic change in the human arts.