The new views that have thus arisen have been definitely summarised and clearly contrasted with Darwinism by the botanist Korschinsky. He died before completing his general work, “Heterogenesis und Evolution,” but he has elsewhere(55) given an excellent summary of his results, which we append in abstract.
DARWIN. (1) Everything organic is capable of variation. Variations arise in part from internal, in part from external causes. They are slight, inconspicuous, individual differences.
KORSCHINSKY AND THE MODERNS. (1) Everything organic is capable of variation. This capability is a fundamental, inherent character of living forms in general, and is independent of external conditions. It is usually kept latent by “heredity,” but occasionally breaks forth in sudden variations.
DARWIN. (2) The struggle for existence. This combines, increases, fixes useful variations, and eliminates the useless. All the characters and peculiarities of a finished species are the results of long-continued selection; they must therefore be adapted to the external conditions.
KORSCHINSKY AND THE MODERNS. (2) Saltatory variations.—These are, under favourable circumstances, the starting-point of new and constant races. The characters may sometimes be useful, sometimes quite indifferent, neither advantageous nor disadvantageous. Sometimes they are not in harmony with external circumstances.
DARWIN. (3) The species is subject to constant variation. It is continually subject to selection and augmentation of its characters. Hence again the origin of new species.
KORSCHINSKY AND THE MODERNS. (3) All fully developed species persist, but through heterogenesis a splitting up into new forms may take place, and this is accompanied by a disturbance of the vital equilibrium. The new state is at first insecure and fluctuating, and only gradually becomes stable. Thus new forms and races arise with gradual consolidation of their constitution.
DARWIN. (4) The sharper and more acute the effect of the environment, the keener is the struggle for existence, and the more rapidly and certainly do new forms arise.
KORSCHINSKY AND THE MODERNS. (4) Only in specially favourable conditions, only when the struggle for existence is weak, or when there is none, can new forms arise and become fixed. When the conditions are severe no new forms arise, or if they do they are speedily eliminated.
