What the Argument from Design Had Been

To see what changed in 1859 it helps to know what was being taught before it. William Paley's Natural Theology of 1802 opens with a man crossing a heath who finds a watch and concludes, from the fitting of its parts to a purpose, that it had a maker. Paley then works through the eye, the ear, the joints and the circulation of the blood, arguing at every step that the same inference holds and holds more strongly. This was not a fringe position. It was a set text at Cambridge, where Darwin read it as an undergraduate preparing for ordination, and he said later that he had been charmed by its logic.

Natural selection removes the inference without denying the observation. Organisms really are fitted to their conditions, sometimes exquisitely, and the fitting is real and needs an explanation; but heritable variation plus differential survival, over enough time, will produce it with no aim in view and nobody choosing. Darwin was careful about how far he pushed this. On the Origin of Species closes with a sentence about life having been breathed into a few forms or into one, and the argument nowhere requires atheism. What it does require is that adaptation stop being evidence, and that took the strongest natural argument for God then available out of service.