The great chapter on Natural Selection, or the preservation of favourable and the rejection of injurious variations, is crowded with striking passages. One of these vividly contrasts man's selection with nature's. "Man can act only on external and visible characters: nature cares nothing for appearances, except in so far as they may be useful to any being. She can act on every internal organ, on every shade of constitutional difference, on the whole machinery of life. Man selects only for his own good; nature only for that of the being she tends. Every selected character is fully exercised by her; and the being is placed under well-suited conditions of life.... Under nature, the slightest difference of structure or constitution may well turn the nicely-balanced scale in the struggle for life, and so be preserved. How fleeting are the wishes and efforts of man! how short his time! and consequently how poor will his products be, compared with those accumulated by nature during whole geological periods. Can we wonder, then, that nature's productions should be far 'truer' in character than man's productions; that they should be infinitely better adapted to the most complex conditions of life, and should _plainly bear the stamp of far higher workmanship_?" The words in italics certainly are a good answer to those who think Darwin had any tendency to depreciate the marvels of nature by bringing them under the law of natural selection. But we shall gain further light on this subject later on. The main argument may be summed up thus: if variations beneficial to any creature occur, which cannot be doubted, the individuals in whom they occur will have the best chance of surviving and transmitting their qualities to their offspring. This natural selection will tend to produce divergence of character among offspring, and to intensify differences until they equal those between species or even genera. The same tendency to improvement brings about the decay and ultimate extinction of many lower and unimproved forms of life.