Look, I don't want to get into the weeds of this because personally I don't think it's relevant to the issue of intelligence, but here's a list of things I think are evident about consciousness:
1. People have different kinds of conscious experience (just talk to other humans to get the picture).
2. Consciousness varies, and can be present or not-present at any given moment (sleep, death, hallucinogenic drugs, anaesthesia).
3. Many things don't have the properties of consciousness that I attribute to my subjective experience (rocks, maybe lifeforms that don't have nerve cells, lots of unknowns here).
Given this, it's obvious that consciousness can be created from non-consciousness, you need merely to have sex and wait 9 months. Add to that the fact that humans weren't a thing a million years ago, for instance, and you have to conclude that it's possible for an optimisation system to produce consciousness eventually (natural selection).