2. All creatures tend in a general way to resemble their parents in appearance more closely than they resemble individuals not related to them. This may be termed the law of heredity. 3. Each pair of organisms produces in the course of a lifetime, on an average, many more than two young ones. 4. On an average the total number of each species remains stationary. From (3) and (4) follows the doctrine of Malthus, namely, that many more individuals are born than can reach maturity. Darwin applied this doctrine to the whole of the animal and the vegetable kingdoms. In his introduction to _The Origin of Species_ he writes:—“As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary, however slightly, in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.” In other words, the struggle for existence amongst all organic beings throughout the world, which inevitably follows from the high geometrical ratio of their increase, results in the survival of the fittest, that is to say, of those best adapted to cope with their enemies and to secure their food. Since organisms are thus naturally selected in nature, we may speak of a natural selection which acts in much the same way as the human breeder does. Darwin’s theory, then, is that all the variety of organisms which now exist have been evolved from one or more forms by this process of natural selection. Various Anti-Darwinian Views The objections which have been urged against the theory of natural selection fall into two classes. I. Those which strike at its root, which either deny that there is any natural selection, or declare that it is not capable of producing a new species. II. Those which are directed against the all-sufficiency of natural selection to account for organic evolution. Those of the first class need not detain us long, although among those who formulate them are to be found some eminent men of science. Delage alleges that selection is powerless to form species, its function is, according to him, limited to the suppression of variations radically bad, and to the maintaining of a species in its normal character. It is thus an inimical factor in evolution, a retarder rather than an accelerator of species-change. It merely acts by preserving the type at the expense of the variants, and so acts as a brake on evolution. Korschinsky, while possibly not denying that selection occurs in nature, declares that its influence on evolution is _nil_, or, if it has any influence, that it is a hindering one.