As to the sterility of hybrids, that can no longer be insisted upon as absolutely true, nor be practically used as a test between species and varieties, unless we allow that hares and rabbits are of one species. That it subserves a purpose in keeping species apart, and was so designed, we do not doubt. But the critics fail to perceive that this sterility proves nothing against the derivative origin of the actual species; for it may as well have been intended to keep separate those forms which have reached a certain amount of divergence as those which were always thus distinct.
The argument for the permanence of species, drawn from the identity with those now living of cats, birds, and other animals, preserved in Egyptian catacombs, was good enough as used by Cuvier against St. Hilaire, that is, against the supposition that time brings about a gradual alteration of whole species; but it goes for little against Darwin, unless it be proved that species never vary, or that the perpetuation of a variety necessitates the extinction of the parent breed. For Darwin clearly maintains—what the facts warrant—that the mass of a species remains fixed so long as it exists at all, though it may set off a variety now and then. The variety may finally supersede the parent form, but it may coexist with it; yet it does not in the least hinder the unvaried stock from continuing true to the breed, unless it crosses with it. The common law of inheritance may be expected to keep both the original and the variety mainly true as long as they last, and none the less so because they have given rise to occasional varieties. The tailless Manx cats, like the fox in the fable, have not induced the normal breeds to dispense with their tails, nor have the Dorkings (apparently known to Pliny) affected the permanence of the common sort of fowl.
As to the objection, that the lower forms of life ought, on Darwin's theory, to have been long ago improved out of existence, replaced by higher forms, the objectors forget what a vacuum that would leave below, and what a vast field there is to which a simple organization is best adapted, and where an advance would be no improvement, but the contrary. To accumulate the greatest amount of being upon a given space, and to provide as much enjoyment of life as can be under the conditions, seems to be aimed at, and this is effected by diversification.
Finally, we advise nobody to accept Darwin's, or any other derivative theory, as true. The time has not come for that, and perhaps never will. We also advise against a similar credulity on the other side, in a blind faith that species—that the manifold sorts and forms of existing animals and vegetables—"have no secondary cause." The contrary is already not unlikely, and we suppose will hereafter become more and more probable. But we are confident, that, if a derivative hypothesis ever is established, it will be so on a solid theistic ground.
Meanwhile an inevitable and legitimate hypothesis is on trial,—an hypothesis thus far not untenable,—a trial just now very useful to science, and, we conclude, not harmful to religion, unless injudicious assailants temporarily make it so.
One good effect is already manifest: its enabling the advocates of the hypothesis of a multiplicity of human species to perceive the double insecurity of their ground. When the races of men are admitted to be of one species, the corollary, that they are of one origin, may be expected to follow. Those who allow them to be of one species must admit an actual diversification into strongly marked and persistent varieties, and so admit the basis of fact upon which the Darwinian hypothesis is built; while those, on the other hand, who recognize a diversity of human species, will hardly be able to maintain that such species were primordial and supernatural in the common sense of the word.
The English mind is prone to positivism and kindred forms of materialistic philosophy, and we must expect the derivative theory to be taken up in that interest. We have no predilection for that school, but the contrary. If we had, we might have looked complacently upon a line of criticism which would indirectly, but effectively, play into the hands of positivists and materialistic atheists generally. The wiser and stronger ground to take is, that the derivative hypothesis leaves the argument for design, and therefore for a Designer, as valid as it ever was;—that to do any work by an instrument must require, and therefore presuppose, the exertion rather of more than of less power than to do it directly;—that whoever would be a consistent theist should believe that Design in the natural world is coextensive with Providence, and hold fully to the one as he does to the other, in spite of the wholly similar and apparently insuperable difficulties which the mind encounters whenever it endeavors to develop the idea into a complete system, either in the material and organic, or in the moral world. It is enough, in the way of obviating objections, to show that the philosophical difficulties of the one are the same, and only the same, as of the other.
[Footnote 1: Whatever it may be, it is not "the homoeopathic form of the transmutative hypothesis," as Darwin's is said to be, (p. 252, Amer. reprint,) so happily that the prescription is repeated in the second (p. 259) and third (p. 271) dilutions, no doubt, on Hahnemann's famous principle, with an increase of potency at each dilution. Probably the supposed transmutation is per saltus. "Homoeopathic doses of transmutation," indeed! Well, if we really must swallow transmutation in some form or other, as this reviewer intimates, we might prefer the mild homoeopathic doses of Darwin's formula to the allopathic bolus which the Edinburgh general practitioner appears to be compounding.]
[Footnote 2: Vide North American Review, for April, 1860, p. 475, and Christian Examiner, for May, p. 457.]
[Footnote 3: Page 188, English ed.]