To reach a definition that will include these {96} let us begin by fixing our attention on that order of facts which formed the special study of Darwin, and in connection with which the theory of evolution became first known to the world; and let us ask what was the greatest and the most notorious effect produced by Darwinism on human thought generally. Its greatest and most notorious effect was to disprove, or rather render superfluous, the old theory which explained the varieties of organic life by referring them to the design of some quasi-human intelligence. According to the old theory, every species of living thing, from the lowest to the highest, was produced by the power and purpose of one supreme Mind, who adapted the frame and faculties of each to a prearranged set of circumstances and the fulfilment of certain needs. According to the theory of evolution, associated with the name of Darwin, these results were accomplished by purpose and intelligent power likewise, only not by the power and purpose of one supreme external Mind, but by the power and purpose of the living things themselves. Each living thing chose its mates, reproduced its kind, hunted for food, fought with rivals, and either conquered or was conquered by them, in obedience to the promptings of its own instinctive purposes. These were the motive power of the whole evolutionary process. The variety and development of organic life, as we know it, did not result indeed from one great intention, but it did result from an infinity of little intentions. {97} Now so far the theory of design and the theory of evolution very closely resemble each other; but here we come to the point of essential difference between them. According to the theory of design, the varieties and gradations of organic life were not only the result of intention in the supreme Mind, but were also themselves the exact result intended. According to the evolutionary theory, although they were the result of an infinity of intentions, not one of the living things, from whose intention they resulted, intended them. They were the by-product of actions undertaken for entirely different ends—that is to say, for the benefit of the individual creatures who undertook them. This is the essential and this is the peculiar character with which the theory of evolution invested them. It presented to the mind the extraordinary phenomenon of a single series of actions producing a double series of results—the intended and the unintended, the latter of which, though entirely different from the former, was equally orderly, equally reasonable and coherent. Evolution, in fact, as revealed to us in the physiological world, is, for the philosopher, neither more nor less than this—the _reasonable sequence of the unintended_.