Evolution has brought about creatures that are more successful (in regard to survival and reproduction), the more predictive power they have about their environment[1]. One could say, the better a species can simulate it's environment, the more likely it will continue to exist and be part of the ongoing evolution. Our brains are of course also just products of this evolutionary process and meanwhile very good at simulating their environment.
Now if we think about Plato's cave we could say, that all our experience is just an illusion. It's all just a projection of reality, that our brain creates. I'd go a step further and say: Experience or qualia is what the process of simulation of reality feels like. Or to put it in another way: Conciousness is the process of simulation of reality. The "better" the simulation or the more complete and closer to "reality" it is (whatever that means) - the higher the form of conciousness.
Taking this definition one must also concede that even animals and "lower" life forms have some degree of conciousness. It probably feels like something to be a streptococcus.
Of course all this is just blind speculation - but it somehow feels right to me.
[1] https://www.quantamagazine.org/20151119-life-is-information-...