Now we come to the elephant in the room. Darwin’s theory was incomplete. When the theory was completed, would natural selection prove to be that effective? Although he threw in a lot of assorted, presumed-relevant facts, no one, starting with Darwin, had much idea about the nature of variation – how it comes, what form it takes, how regular it is. And, without this knowledge, given that natural selection supposedly works on this variation, it is hard to make definite judgments about its effectiveness; especially since Darwin stressed that, although variation has causes, it is random in the sense of not appearing according to need. When he was not pushing the Lamarckian alternative, he was adamant that it is selection alone that is responsible for adaptation.