Maybe someone else already said this, but evolution doesn't state that chimps turned into humans. Evolution states that chimps and humans have a common ancestor. I didn't evolve into my sister. We both evolved from our common ancestors. (I actually don't have a sister, but we will pretend I do for the sake of argument.)

Here's a good analogy for you:

Some Catholics became Anglicans. Others became Lutherans. Yet we still have Catholics. Clearly some members of a population can change over time (I won't call the Protestant Reformation an evolution) while other members of the same population, influenced by the same stimuli, can stay the same.