A more ample discussion of the origin of species is not within the scope of this book. But I may say that until recently the conception that _every_ organ, part and feature of a plant and animal _must_ be explained, and can _only_ be explained, as being of life-saving value to its possessor, and accordingly "selected" and preserved in the struggle for existence, was held by many "Darwinians" in too uncompromising a spirit. This conception was, really from the first, qualified by the admission that the life-saving value and consequent preservation of a structure must undoubtedly in some cases have been in operation in ancestors of the existing species, and is no longer operative in their descendants although they inherit the structure which has now become useless. Moreover, the operation of those subtle laws of nutrition and of form which are spoken of as the "correlation of parts in growth and in variation" (mentioned on p. 119) was pointed out by Darwin himself as probably accounting for many remarkable growths, structures and colour-marks which we cannot imagine to be now, or ever to have been in past ancestry, of a life-saving value. Nevertheless, the old "teleology," according to which, in pre-Darwinian days, it was held that every part and feature of an animal or plant has been specially created to fulfil a definite pre-ordained function or useful purpose, still influenced the minds of many naturalists. Natural selection and survival of the fittest were reconciled with the old teleological scheme, and it was held that we must as good Darwinians account for every structure and distinctive feature in every animal and plant as due to its life-saving value. Herbert Spencer's term, "the survival of the _fittest_," conduced to the diffusion of this extreme view: Darwin's equivalent term, "the preservation of _favoured_ races," did not raise the question of greater or less fitness. The extreme view is now, however, giving place to the recognition of the fact that the actual tendencies to variation–accumulated in the living substance of the various stocks or lines of descent and handed on during an immense succession of ages of change by hereditary transmission–counts for more in the production of new species and strange, divergent, even grotesque forms of both animals and plants than had been supposed.