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. DARWIN. (5) The chief condition of evolution is therefore the struggle for existence and the selection which this involves. KORSCHINSKY AND THE MODERNS. (5) The struggle for existence simply decimates the overwhelming abundance of possible forms. Where it occurs it prevents the establishment of new variations, and in reality stands in the way of new developments. It is rather an unfavourable than an advantageous factor. DARWIN. (6) If there were no struggle for existence there would be no adaptation, no perfecting. KORSCHINSKY AND THE MODERNS. (6) Were there no struggle for existence, there would be no destruction of new forms, or of forms in process of arising. The world of organisms would then be a colossal genealogical tree of enormous luxuriance, and with an incalculable wealth of forms. DARWIN. (7) Progress in nature, the “perfecting” of organisms, is only an increasingly complex and ever more perfect adaptation to the external circumstances. It is attained by purely mechanical methods, by an accumulation of the variations most useful at the time.