No, we have much more than assumptions, much more than faith. We have evidence. The theory makes reliable, repeatable predictions about reality.
Much like the theory of gravity. Or do you find the theory of gravity lacks proof as well?
Theory of gravity? I thought it was a law. Look, we have never witnessed one species turn into another, therefore, yes, it is faith. Actually, NOTHING can be proven. God can't be proven. We can't prove that life evolved as you say it has. Transitional fossils, even evolutionists, agree that they are missing, tons of them are NOT there to see. We NEVER see half an alligator, or half a bird. Where are all the fossils? We've just gotten unlucky with our digging?