it may well be a gradual process. But Darwin's book titled the ORIGIN of the Species is making an incorrect claim. in order for any process of evolution to begin, his theory had to appropriate (take) 'something' already in existence. As such, that 'something' possesses a PRIOR claim to the actual ORIGIN of the species. Darwin appropriated then built his theory upon that 'something'.
Darwin was quite guy, wasn't he?
Although I think it's a bit of an overstatement myself, philosopher Daniel Dennett called Darwin's idea the best idea man had ever had:
"If I were to give an award for the single best idea anyone has ever had, I'd give it to Darwin, ahead of Newton and Einstein and everyone else. In a single stroke, the idea of evolution by natural selection unifies the realm of life, meaning, and purpose with the realm of space and time, cause and effect, mechanism and physical law." - Daniel Dennett
Dawkins added, "We explain our existence by a combination of the anthropic principle and Darwin’s principle of natural selection. That combination provides a complete and deeply satisfying explanation for everything that we see and know." and "Although atheism might have been logically tenable before Darwin, Darwin made it possible to be an intellectually fulfilled atheist"
I'd say that ideas like justice and rational skepticism were greater ideas, but we're up in the stratosphere of man's greatest intellectual achievements however we rank them.