Another characteristic of Darwin’s mental processes is his way of meeting difficulties. The born reasoner is apt to slur over obstacles and objections, to devote himself with endless ingenuity to eliminating them rather than facing them squarely. Darwin was ingenious enough, but he did not dodge difficulties. Instead of doing so, his propensity was, if anything, to make them and seek them. It was said of Pasteur, so like Darwin in many points: ‘No adversary of M. Pasteur had formulated this argument; but M. Pasteur, who had within himself an ever-present adversary, always on the watch and determined to yield only to the force of accumulated evidence, himself raised the objection.’[67] So Darwin. As he himself records, and no thinker ever laid down a more significant principle or one more revealing for his own mental constitution: ‘I had, also, during many years followed a golden rule, namely, that whenever a published fact, a new observation or thought came across me, which was opposed to my general results, to make a memorandum of it without fail and at once; for I had found by experience that such facts and thoughts were far more apt to escape from the memory than favorable ones.’[68] And the intense consciousness of objections and difficulties appears even more vividly in the sentence: ‘I cannot too strongly express my conviction of the general truth of my doctrines, and God knows I have never shirked a difficulty.’[69] The recognition of obstacles and complications constantly popping up from everywhere naturally necessitated endless revision and recasting. Here again, the habitual reasoner, having once set his mould is reluctant to alter it. Not so Darwin. There are indeed times when even he rebels and declares that it will be more fruitful to follow new paths than to be perpetually adjusting the old. But in general his readiness to alter and reconstruct is unlimited. He revises and works over his books. In doing so he showed his characteristic disposition to accept and defer to the judgment of others. How charming is his daughter’s account of this: ‘He was always so ready to be convinced that any suggested alteration was an improvement, and so full of gratitude for the trouble taken. I do not think that he ever used to forget to tell me what improvement he thought that I had made, and he used almost to excuse himself if he did not agree with any correction. I think I felt the singular modesty and graciousness of his nature through thus working for him in a way I never should otherwise have done.’[70] There is no better way to appreciate the extent and the persistence of Darwin’s revision than to make even a cursory comparison of the first and the last editions of the ‘Origin.’ Almost every page shows minor or considerable changes, and while some are no doubt mere matters of language, many have a bearing, however slight, on the trend of the reasoning, deepening, or strengthening, or clarifying it.