More than 40 years later, Sharpe can still recall the Darwinian analogy that Alchian used to convey the irrelevance of the verisimilitude of assumptions: `Assume that creatures crawled up from the primordial slime, looked around and decided that for maximum effect they should grow opposable thumbs." The assumption that anatomical change resulted from conscious judgment of usefulness was plainly absurd, but "the prediction of the model [the development of opposable thumbs] would be correct, even though the actual mechanism (evolution) was very different."

Donald MacKenzie, An Engine, Not a Camera, loc. 244