I believe nature is all there is. If we could replicate a human brain several times, and make each 'human brain' receive the exact same input data (sounds, sights, smells e.t.c.) from the moment they 'exist' until the end of their lifetime, I truly think that each of these brains will make precisely the same decisions (and each of these 'brains' would think they were conscious and in control of their lives).

In my eyes, consciousness is simply a natural phenomenon that can be explained but we just lack the understanding at this moment. Time and time again we have made this mistake of assuming there is something supernatural about the things we cannot comprehend and only a few centuries later it is completely understood scientifically. I think consciousness will be a similar case but will take more time.