We have seen also that a marked tendency to reversion does exist, inasmuch as it sometimes takes place in a striking manner, as exemplified in the white silk fowl in England, in spite of careful selection in breeding.
Again, we have seen that a tendency exists in nature to eliminate hybrid races, by whatever means that elimination is effected, while no similar tendency bars the way to an indefinite blending of varieties. This has also been enforced by statements as to the prepotency of certain pollen of identical species, but of distinct races.
To all the preceding considerations have been added others derived from the relations of species to past time. It has been contended that we have as yet no evidence of minutely intermediate forms connecting uninterruptedly together undoubtedly distinct species. That while even "horse ancestry" fails to supply such a desideratum, in very strongly marked and exceptional kinds (such as the Ichthyosauria, Chelonia, and Anoura), the absence of links is very important and significant. For if
every species, without exception, has arisen by minute modifications, it seems incredible that a small percentage of such transitional forms should not have been preserved. This, of course, is especially the case as regards the marine Ichthyosauria and Plesiosauria, of which such numbers of remains have been discovered.
Sir William Thomson's great authority has been seen to oppose itself to "Natural Selection," by limiting, on astronomical and physical grounds, the duration of life on this planet to about one hundred million years. This period, it has been contended, is not nearly enough on the one hand for the evolution of all organic forms by the exclusive action of mere minute, fortuitous variations; on the other hand, for the deposition of all the strata which must have been deposited, if minute fortuitous variation was the manner of successive specific manifestation.
Again, the geographical distribution of existing animals has been seen to present difficulties which, though not themselves insurmountable, yet have a certain weight when taken in conjunction with all the other objections.
The facts of homology, serial, bilateral and vertical, have also been passed in review. Such facts, it has been contended, are not explicable without admitting the action of what may most conveniently be spoken of as an internal power, the existence of which is supported by facts not only of comparative anatomy but of teratology and pathology also. "Natural Selection" also has been shown to be impotent to explain these phenomena, while the existence of such an internal power of homologous evolution diminishes the a priori improbability of an analogous law of specific origination.
All these various considerations have been supplemented by an endeavour to show the utter inadequacy of Mr. Darwin's theory with regard to the higher psychical phenomena of man (especially the evolution of moral conceptions), and with regard to the evolution of individual organisms by the action of
Pangenesis. And it was implied that if Mr. Darwin's latter hypothesis can be shown to be untenable, an antecedent doubt is thus thrown upon his other conception, namely, the theory of "Natural Selection."
A cumulative argument thus arises against the prevalent action of "Natural Selection," which, to the mind of the Author, is conclusive. As before observed, he was not originally disposed to reject Mr. Darwin's fascinating theory. Reiterate endeavours to solve its difficulties have, however, had the effect of convincing him that that theory as the one or as the leading explanation of the successive evolution and manifestation of specific forms, is untenable. At the same time he admits fully that "Natural Selection" acts and must act, and that it plays in the organic world a certain though a secondary and subordinate part.