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which as to details is of different kinds, and produced in different ways in different species. To develop “beauty and singularity of plumage ” is a character of the group, but not of any one definite kind, to be explained merely by inheritance.
Again, we have the very curious horned flies1 which agree indeed in a common peculiarity, but in one singularly different in detail in different species, and not known to have any protecting effect.
Amongst plants also we meet with similar resemblances. The great group of Orchids includes species which exhibit strange and bizarre approximations to different animal forms, and which have often the appearance of cases of inimicry, as it were in an incipient stage.
The number of similar instances which could be brought forward from amongst animals and plants is very great, but the examples given are, it is hoped, amply sufficient to point towards the conclusion which other facts will establish, viz. that there are causes operating in the evocation of these harmonious diverging resenıblances) other than “Natural Selection," or heredity, and other even than merely geographical, climatal, or any simply external conditions.
Many cases have been adduced of striking likenesses between different animals, not due to inheritance; but this should be the less surprising, in that the very same individual presents us with likenesses between different parts of its body (e.g. between the several joints of the backbone), which are certainly not explicable by inheritance. This, however, leads to a rather large subject, which will be treated of in the eighth chapter of the present work,
i Loc. cit. p. 314.
Here it will be enough to affirm (leaving the proof of the assertion till later) that parts are often homologous which have no direct genetic relationship-a fact which harmonizes well with the other facts here given, but which “Natural Selection,” pure and simple, seems unable to explain.
But surely the independent appearance of similar organic forms is what we might expect, a priori, from the independent appearance of similar inorganic ones. As Mr. G. H. Lewes well observes: 1 "We do not suppose the carbonates and phosphates found in various parts of the globe-we do not suppose that the families of alkaloids and salts have any nearer kinship than that which consists in the similarity of their elements, and the conditions of their combination. Hence, in organisms, as in salts, morphological identity may be due to a community of causal connexion, rather than community of descent.”
“ Mr. Darwin justly holds it to be incredible that individuals identically the same should have been produced through Natural Selection from parents specifically distinct; but he will not deny that identical forms may issue from parents genetically distinct, when these parent forms and the conditions of production are identical. To deny this would be to deny the law of causation.”
Professor Huxley has, however, suggested 2 that such mineral identity may be explained by applying also to minerals a law of descent; that is, by considering such similar forms as the descendants of atoms which inhabited one special part of the primitive nebular cosmos, each considerable space of which may be supposed to have been under the influence of somewhat different conditions.
Fortnightly Review, New Series, vol. iii. (April 1868), p. 372.
Surely, however, there can be no real parity between the relationship of existing minerals to nebular atoms, and the relationship of existing animals and plants to the earliest organisms. In the first place, the latter have produced others by generative multiplication, which mineral atoms never did. In the second, existing animals and plants spring from the living tissues of preceding animals and plants, while existing minerals spring from the chemical affinity of separate elements. Carbonate of soda is not formed, by a process of reproduction, from other carbonate of soda, but directly by the suitable juxtaposition of carbon, oxygen, and sodium.
Instead of approximating animals and minerals in the mode suggested, it may be that they are to be approximated in quite a contrary fashion ; namely, by attributing to mineral species an internal innate power. For, as we must attribute to each elementary atom an innate power and tendency to form (under the requisite external conditions) certain unions with other atoms, so we may attribute to certain mineral species—as crystals—an innate power and tendency to exhibit (the proper conditions being supplied) a definite and symmetrical external form. The distinction between animals and vegetables on the one hand, and minerals on the other, is that, while in the organic world close similarity is the result sometimes of inheritance, sometimes perhaps of direct production independently of parental action, in the inorganic world the latter is the constant and only mode in which such similarity is produced.
When we come to consider the relations of species to space--in other words, the geographical distribution of organisms—it will be necessary to return somewhat to the subject of the independent origin of closely similar forms,
in regard to which some additional remarks will be found towards the end of the seventh chapter.
In this third chapter an effort has been made to show that while on the Darwinian theory concordant variations are extremely improbable, yet Nature presents us with abundant examples of such; the most striking of which are, perhaps, the higher organs of sense. Also that an important influence is exercised by conditions connected with geographical distribution, but that a deeper-seated influence is at work, which is hinted at by those special tendencies in definite directions, which are the properties of certain groups. Finally, that these facts, when taken together, afford strong evidence that “Natural Selection” has not been the exclusive or predominant cause of the various organic structural peculiarities. This conclusion has also been re-enforced by the consideration of phenomena presented to us by the inorganic world.
MINUTE AND GRADUAL MODIFICATIONS.
There are difficulties as to minute modifications, even if not fortuitous.
Examples of sudden and considerable modifications of different kinds. -Professor Owen's view.-Mr. Wallace. – Professor Huxley.- Objections to sudden changes. - Labyrinthodont. - Potto.—Cetacea. -As to origin of bird's wing.-Tendrils of climbing plants.—Animals once supposed to be connecting links.—Early specialization of structure. – Macrauchenia. —Glyptodon.-Sabre-toothed tiger.—Conclusion.
Not only are there good reasons against the acceptance of the exclusive operation of “Natural Selection” as the one means of specific origination, but there are difficulties in the way of accounting for such origination by the sole action of modifications which are insignificant and minute whether fortuitous or not.
Arguments may yet be advanced in favour of the view that new species have from time to time manifested themselves with suddenness, and by modifications appearing at once (as great in degree as are those which separate Hipparion from Equus), the species remaining stable in the intervals of such modifications : by stable being meant that their variations only extend for a certain degree in various directions, like oscillations in a stable equilibrium. This is the conception of Mr. Galton, who compares the
1 “Hereditary Genius, an Inquiry into its Laws,” &c. By Francis Galton, F.R.S. (London : Macmillan.)