My hypothesis (FWIW) is that consciousness is elemental, just like space-time, mass-energy, there is consciousness-information. That side steps the issue of how consciousness emerged from unconscious matter. But anyway, I won't try to prove it because it's just a crazy-ass hypothesis. But, suppose that consciousness can "occupy" any organism with a complex enough brain to support the "interface" between matter and consciousness. That implies two things: 1) Single-celled, or multi-cellular pre-chordates in general, do not have the hardware to support that interface. and 2) any sufficiently complex computer AI could act as a host to consciousness.
Anyway, as crazy-ass half-baked hypotheses goes, at least it has a certain consistency to it. 
For the most part, however, I don't take any of my crazy-ass hypotheses seriously enough to worry about such details. 
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