Did Charles Darwin and other evolutionists question the theory of evolution?

In a way they did. Charles Darwin, when talking about the complexity of the eye in his Origin of The Species, said,"To suppose that the eye....could have been formed by natural selection, seems, I freely confess, absurd in the highest degree." Sir Arthur Keith, another evolutionist said,"Evolution is unproved and unprovable. We believe it because the only alternative is special creation, and that is unthinkable." There are other quotes like these; this must show that it is impossible for even the most knowledgeable evolutionists to prove that evolution actually occurred.