Harris seems to presuppose the old Cartesian framework, with consciousness being that which is indubitable and which can in no way be reduced to matter. I wonder, though, what concept of matter Harris is working with here? That “matter” is a concept should go without saying, since on his Cartesian view of consciousness, we are locked in a mental prison with no way of perceiving anything outside our own minds. We can have knowledge of matter, but only as a mathematical abstraction (see my review of Latour’s Modes of Existence, where he deconstructs the modern “idea of matter”).
Harris admits that, from within the materialist ontological paradigm, consciousness may always appear to be a miracle, its origins a mystery. Rather than rest content with this sort of quasi-dualist materialist obscurantism, I’d rather follow the heretical panpsychist (broadly construed) stream dating back to Spinoza, Leibniz, and Schelling, later emerging in the organic realism of Whitehead. For a fuller treatment of why an evolutionary panpsychism provides a more coherent account of the place of consciousness in nature, see my article: “The Varieties of Physicalist Ontology: Whitehead’s Process-Relational Alternative” (2020).