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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 toward 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 reënforced 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.-Prof. Owen's View.— Mr. Wallace—Prof. Huxley–Objections to Sudden Changes—LabyrinthodontPotto.—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 infinitesimal and minute, whether fortuitous or not. .
Arguments may yet be advanced in favor 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 development of species with a many-facetted spheroid tumbling over from one facet, or stable equilibrium, to another. The existence of internal conditions in animals corresponding with such facets is denied by pure Darwinians, but it is contended in this work, though not in this chapter, that something may also be said for their existence. The considerations brought forward in the last two chapters, namely, the difficulties with regard to incipient and closely-similar structures respectively, together with paleontological considerations to be noticed later, appear to point strongly in the direction of sudden and considerable changes. This is notably the case as regards the young oysters already mentioned, which were taken from the shores of England and placed in the Mediterranean, and at once altered their mode of growth and formed prominent diverging rays, like those of the proper MediterTanean oyster; as also the twenty-nine kinds of American trees, all differing from their nearest European allies similarly—“leaves less toothed, buds and seeds smaller, fewer branchlets,” etc. To these may be added other facts given by Mr. Darwin. Thus he says, that “climate, to a certain extent, directly modifies the form of dogs.”” The Rev. R. Everett found that setters at Delhi, though most carefully paired, yet had young with “nostrils more contracted, noses more pointed, size inferior, and limbs more slender.” Again, cats at Mombas, on the coast of Africa, have short, stiff hairs, instead of fur; and a cat at Algoa Bay, when left only eight weeks at Mombas, “underwent a complete metamorphosis, having parted with its sandy-colored fur.” The conditions of life seem to produce a considerable effect on horses, and instances are given by Mr. Darwin of pony breeds" having independently arisen in different parts of the world, possessing a certain similarity in their physical conditions. Also changes due to climate may be brought about at once in a second generation, though no appreciable modification is shown by the first. Thus “Sir Charles Lyell mentions that some Englishmen, engaged in conducting the Operations of the Real del Monte Company in Mexico, carried out with them some greyhounds, of the best breed, to hunt the hares which abound in that country. It was found that the greyhounds could not support the fatigues of a long chase in this attenuated atmosphere, and, before they could come up with their prey, they lay down gasping for breath; but these same animals have produced whelps, which have grown up, and are not in the least degree incommoded by the want of density in the air, but run down the hares with as much ease as do the fleetest of their race in this country.” " We have here no action of “Natural Selection; ” it was not that certain puppies happened accidentally to be capable of enduring more rarefied air, and so survived, but the offspring were directly modified by the action of surrounding conditions. Neither was the change elaborated by minute modifications in many successive generations, but appeared at once in the second. With regard once more to sudden alterations of form, Nathusius is said to state positively as to pigs," that the result of common experience and of his experiments was that rich and abundant food, given during youth, tends by some direct action to make the head broader and shorter. Curious jaw appendages often characterize Normandy pigs, according to M. Eudes Deslongchamps. Richardson figures these appendages on the old “Irish greyhound pig,” and they are said by Nathusius to appear occasionally in all the long-eared races. Mr. Darwin observes,” “As no wild pigs are known to have analogous appendages, we have at present no reason to suppose that their appearance is due to reversion; and if this be so, we are forced to admit tha
* “Psereditary Genius, an Inquiry into its Laws,” etc. By Francis Galton, F. R. S. (London: Macmillan.)
* Carpenter’s “Comparative Physiology,” p. 987, quoted by Mr. J. J.
Murphy, “Habit and Intelligence,” vol. i., p. 171.
somewhat complex, though apparently useless structures may be suddenly developed without the aid of selection.” Again, “Climate directly affects the thickness of the skin and hair” of cattle.” In the English climate an individual Porto Santo rabbit" recovered the proper color of its fur in rather less than four years. The effect of the climate of India on the turkey is considerable. Mr. Blyth "describes it as being much degenerated in size, “utterly incapable of rising on the wing,” of a black color, and “with long pendulous appendages over the beak enormously developed.” Mr. Darwin again tells us that there has suddenly appeared in a bed of common broccoli a peculiar variety, faithfully transmitting its newly-acquired and remarkable characters; ” also that there have been a rapid transformation and transplantation of American varieties of maize with a European variety; * that certainly “the Ancon and Manchamp breeds of sheep,” and that (all but certainly) Niata cattle, turnspit and pug dogs, jumper and frizzled fowls, short-faced tumbler pigeons, hook-billed ducks, etc., and a multitude of vegetable varieties, have suddenly appeared in nearly the same state as we now see them.” Lastly, Mr. Darwin tells us that there has been an occasional development (in five distinct cases) in England of the “japamned” or “black-shouldered peacock,” (Pavo nigripennis), a distinct species, according to Dr. Sclater,” yet arising in Sir J. Trevelyan's flock composed entirely of the common kind, and increasing, “to the eactinction of the previously-existing breed.”” Mr. Darwin’s only explanation of the phenomena (on the supposition of the
* “Animals and Plants under Domestication,” vol. i., p. 71. * Ibid., p. 114. 10 Quoted, ibid., p. 274. 11 Ibid., p. 324. 1° Ibid., p. 322. * Ibid., vol. ii., p. 414, * Proc. Zool. Soc. of London, April 24, 1860. * “Animals and Plants under Domestication,” vol. i., p. 291.