 John Maynard Smith attributed the phrase to Haldane in a conversation with Paul Harvey in the early 1970s.The philosopher Karl Popper held that any scientific proposition must be falsifiable, in other words it must at least be possible to imagine some reproducible experiment or observation whose outcome would disprove the hypothesis.Initially he thought that Charles Darwin's theory of natural selection (often summarized as "the survival of the fittest") was untestable in this sense, and therefore "almost tautological."