All the hypotheses this chapter explains are exemplary for their naturalism and are either based on or incorporate self-referent models of consciousness. Those of Francis Crick (in collaboration with Christof Koch), Gerald Edelman, and Eugene d’Aquili (in collaboration with Charles D. Laughlin and John McManus) are explicitly self-referent. D’Aquili integrates’ a model of symbolic consciousness into his biological loop hypothesis in a way that brings us to one of the book’s core questions: Why does the human brain symbolize itself as it does?