Consciousness, as the almost metaphysical experience that all humans including myself appear to feel, must have a physical basis. The rationale behind that statement is simple. Our neurons are able to retell that experience, which is the reason we are even able to discuss it.
They wouldn't be able to do that without a physical means of feeling not only the external stimuli and our internal state, but also the metaphysical phenomenon of consciousness that we happen to experience.
This means we should be able to identify the mechanism neurons use to detect it and eventually, once the device is reproduced, close the debate on whether AIs and animals are able to experience consciousness as we know it.
Until that device is discovered, I lean towards the idea of all encompassing consciousness experience(unrelated to thought and intelligence) in all matter and energy that neurons just happen to be able to detect and record. This doesn't advance the discussion as the evolution of conscious neurones cannot be pinpointed. It could be that all neurones are able to detect consciousness, but only brain neurones get the chance to tell anybody other than themselves. Then again, conscious neurones could be a uniquely human development.