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 that of Darwin or as supplementary to it. Before doing this, however, it will be well briefly to summarise the facts and arguments already set forth, because it is only by a clear comprehension of these that the full importance of the theory can be appreciated and its further applications understood.

The theory itself is exceedingly simple, and the facts on which it rests—though excessively numerous individually, and coextensive with the entire organic world—yet come under a few simple and easily understood classes. These facts are,—first, the enormous powers of increase in geometrical progression possessed by all organisms, and the inevitable struggle for existence among them; and, in the second place, the occurrence of much individual variation combined with the hereditary transmission of such variations. From these two great classes of facts, which are universal and indisputable, there necessarily arises, as Darwin termed it, the "preservation of favoured races in the struggle for life," the continuous action of which, under the ever-changing conditions both of the inorganic and organic universe, necessarily leads to the formation or development of new species.

But, although this general statement is complete and indisputable, yet to see its applications under all the complex conditions that actually occur in nature, it is necessary always to bear in mind the tremendous power and universality of the agencies at work. We must never for an instant lose sight of the fact of the enormously rapid increase of all organisms, which has been illustrated by actual cases, given in our second chapter, no less than by calculations of the results of unchecked increase for a few years. Then, never forgetting that the animal and plant population of any country is, on the whole, stationary, we must be always trying to realise the ever-recurring destruction of the enormous annual increase, and asking ourselves what determines, in each individual case, the death of the many, the survival of the few. We must think over all the causes of destruction to each organism,—to the seed, the young shoot, the growing plant, the full-grown tree, or shrub, or herb, and again the fruit and seed; and among animals, to the egg or new-born young, to the youthful, and to the adults. Then, we must always bear in mind that what goes on in the case of the individual or family group we may