Not that I disagree with what he said as he was proven to be right, more surprised by his knowledge over a hundred years ago. How on earth did he know our early gorilla ancestors were not from Paris or Bosnia?
There was no evidence at the time. He put the pieces of the puzzle together through directly observing the world, extensive travelling and study, compiling ideas that were counter-intuitive, confusing, shouldn't fit but did, ideas that were even blasphemous, directly challenging the status quo and challenging his own faith.
It's what is most compelling about the work of Darwin. You can follow his journey, almost feel the moments of realisation as they arrive in his mind, gradually collecting and crystallising into solid theories.
And yeah, gorillas are not our ancestors, but I know what you meant.