Page - 217 - in The Origin of Species

SUMMARY 217 In many cases we are far too ignorant to be enabled to assert that a part or organ is so unimportant for the welfare of a species, that modifications in its structure could not have been slowly accumulated by means of natural selection. In many other cases, modifications are probably the direct result of the laws of variation or of growth, independently of any good having been thus gained. But even such struc- tures have often, as we may feel assured, been subsequently taken advantage of, and still further modified, for the good of species under new conditions of life. We may, also, be- lieve that a part formerly of high importance has frequently been retained (as the tail of an aquatic animal by its terres- trial descendants), though it has become of such small im- portance that it could not, in its present state, have been acquired by means of natural selection. Natural selection can produce nothing in one species for the exclusive good or injury of another ; though it may well produce parts, organs, and excretions highly useful or even indispensable, or again highly injurious to another species, but in all cases at the same time useful to the possessor. In each well-stocked country natural selection acts through the competition of the inhabitants, and consequently leads to suc- cess in the battle for life, only in accordance with the standard of that particular country. Hence the inhabitants of one country, generally the smaller one, often yield to the inhabitants of another and generally the larger country. For in the larger country there will have existed more indi- viduals and more diversified forms, and the competition will have been severer, and thus the standard of perfection will have been rendered higher. Natural selection will not neces- sarily lead to absolute perfection ; nor, as far as we can judge by our limited faculties, can absolute perfection be every- where predicated. On the theory of natural selection we can clearly under- stand the full meaning of that old canon in natural history, "Natura non facit saltum." This canon, if we look to the present inhabitants alone of the world, is not strictly cor- rect; but if we include all those of past times, whether known or unknown, it must on this theory be strictly true. It is generally acknowledged that all organic beings have