Darwin doubted his on theories late in his life, since he could never properly explain the origin of life through his own fossil record.
You can’t tell me scientifically how life was originated, either, nor can you replicate it in a lab. I’m not a creationist, by the way. I’m an agnostic on how life was formed.
Has nothing to do with evolution.
He doubted his own theories at the time. In fact he very helpfully included a list of possible objections to his theory in one of the later chapters of “Origin of species”.
That's precisely my take on it as well. Could evolution be a mechanism within the sphere of existence? Sure. Does it explain or prove the origin of life itself? No. Do I know the answer to this ultimate question? No.
I've taken an interest in the subject after recently being hassled about it by my liberal/confused mother. She asked do I "believe" in evolution." I said science is not about belief--it's about facts. And then explained my view on it, as I just did in the above paragraph.