The modern vogue of Evolution is chiefly owing to Darwin’s investigations as to the origin of species. Darwin formed a strictly biological hypothesis as to the manner in which certain forms of animal life became established, while others died out and disappeared. His theory was that this might be accounted for, partly at least, in the following way. When certain varieties occurred (the cause of their occurrence is still, in the main, unknown), it might be that some of the points, in which they have varied from their parent species or from other species then existing, made them better able to persist in the environment in which they found themselves—less liable to be killed off. They might, for instance, be better able to endure the cold or heat or changes of the climate; better able to find nourishment from what surrounded them; better able to escape from or resist other species which fed upon them; better fitted to attract or master the other sex. Being thus liable to die, their numbers relatively to other species would increase; and that very increase in their numbers might tend towards the extinction of those other species. This theory, to which Darwin gave the name Natural Selection, was also called the theory of survival of the fittest. The natural process which it thus described was called evolution. It was very natural to suppose that evolution meant evolution from what was lower into what was higher; in fact it was observed that at least one species, commonly called higher—the species man—had so survived, and among men again it was supposed that the higher races, ourselves for example, had shewn a tendency to survive the lower, such as the North American Indians. We can kill them more easily than they can kill us. The doctrine of evolution was then represented as an explanation of how the higher species survives the lower. Spencer, for example, constantly uses more evolved as equivalent to higher. But it is to be noted that this forms no part of Darwin’s scientific theory. That theory will explain, equally well, how by an alteration in the environment (the gradual cooling of the earth, for example), quite a different species from man, a species which we think infinitely lower, might survive us. The survival of the fittest does not mean, as one might suppose, the survival of what is fittest to fulfil a good purpose—best adapted to a good end: at the last, it means merely the survival of the fittest to survive; and the value of the scientific theory, and it is a theory of great value, just consists in shewing what are the causes which produce certain biological effects. Whether these effects are good or bad, it cannot pretend to judge. (§ 30 ¶ 1)