Why have humans evolved conciousness?

This is of course a very difficult question but in general if you're talking about consiousness, you have to define what exactly you're talking about in the first place. There are many definitions about what consciousness might be. In general, one might consider that consciousness is for some reason evolutionary advantageous to us and that is also why it evolved in the first place.

We do not know the answer to this yet. Most theorize that the high level of self awareness comes with the level of intelligence. We don't even know if consciousness is a result from evolution.