Here again the possible limit, compatible with a healthy existence, has probably been reached. In like manner, the differences in the size and form of the beak in the various breeds of the domestic pigeon is greater than that between the extreme forms of beak in the various genera and subfamilies of the whole pigeon tribe. From these facts, and many others of the same nature, we may fairly infer, that if rigid selection were applied to any organ, we could in a comparatively short time produce a much greater amount of change than that which occurs between species and species in a state of nature, since the differences which we do produce are often comparable with those which exist. between distinct genera or distinct families."

But in a domestic bird like the fantail where Natural Selection does not come into play, the tail-feathers could hardly be limited by "utility for flight," yet two more tailfeathers could certainly exist in a fancy breed if "utility for flight" were the only obstacle. It seems probable that the real barrier is an internal one in the nature of the organism, and the existence of such is just what is contended for in this chapter. As to the differences between domestic races being greater than those between species or even genera of wild animals, that is not enough for the argument. For upon the theory of "Natural Selection" all birds have a common origin, from which they diverged by insignificant modifications, so that we ought to meet with changes sufficient to warrant the belief that a hornbill could be produced from a creature as different from it as a humming-bird, proportionate time being allowed.

But not only does it appear that there are barriers which oppose change in certain directions, but that there are positive tendencies to development along certain special lines.

In a bird which has been kept and studied like the pigeon, it is difficult to believe that any remarkable spontaneous variations would pass unnoticed by breeders, or that they would fail to be attended to and developed by some one fancier or other. On the hypothesis of indefinite variability, it is then hard to say why pigeons with bills like toucans, or with certain feathers lengthened like those of trogans, or those of birds of paradise, have never been produced. This, however, is a question which may be settled by experiment. Let a pigeon be bred with a bill like a toucan's, and with the two middle tail-feathers lengthened like those of the king bird of paradise, or even let individuals be produced which exhibit any marked tendency of the kind, and the claim to indefinite variability shall be at once conceded.

As yet all the changes which have taken place in pigeons are of a few definite kinds only, such as may be well conceived to be compatible with a species possessed of a certain inherent capacity for considerable yet definite variation, a capacity for the ready production of certain degrees of abnormality which once attained cannot be further increased.

Mr. Darwin himself has already acquiesced in the proposition here maintained, inasmuch as he distinctly affirms the existence of a marked internal barrier to change in certain cases. And if this is admitted in one case, the principle1 is conceded, and it immediately becomes pro

1 Mr. Darwin, in his "Descent of Man," just published, distinctly admits the existence of such internal powers. Thus, in vol. i. p. 154, he says, of the exciting causes of modification, "they relate much more closely to the constitution of the varying organism, than to the nature of the conditions to which it has been subjected." In a note on page 223 he speaks of "incidental results of certain unknown differences in the con

bable that such internal barriers exist in all, although enclosing a much larger field for variation in some cases than in others. Mr. Darwin abundantly demonstrates the variability of dogs, horses, fowls, and pigeons, but he none the less shows clearly the very small extent to which the goose, the peacock, and the guinea-fowl have varied.1 Mr. Darwin attempts to explain this fact as regards the goose by the animal being valued only for food and feathers, and from no pleasure having been felt in it on other accounts. He adds, however, at the end the striking remark," which concedes the whole position, "but the goose seems to have a singularly inflexible organization." This is not the only place in which such expressions are used. He elsewhere makes use of phrases which quite harmonize with the conception of a normal specific constancy, but varying greatly and suddenly at intervals. Thus he speaks of a whole organization seeming to have become plastic, and tending to depart from the parental type. That different organisms should have different degrees of variability, is only what might have been expected a priori from the existence of parallel differences in inorganic species, some of these having but a single form, and others being polymorphic.

3

To return to the goose, however, it may be remarked that it is at least as probable that its fixity of character is

stitution of the reproductive system of the species crossed ;" and in vol. ii. at p. 388 may be read the following passage "In the greater number of cases we can only say that the cause of each slight variation and of each monstrosity lies much more in the nature or constitution of the organism than in the nature of the surrounding conditions; though new and changed conditions certainly play an important part in exciting organic changes of all kinds."

1 "Animals and Plants under Domestication," vol. i. pp. 289-295. 2 "Origin of Species," 5th edition, 1869, p. 45.

3 Ibid. p. 13.

the cause of the neglect, as the reverse. It is by no means unfair to assume that had the goose shown a tendency to vary similar in degree to the tendency to variation of the fowl or pigeon, it would have received attention at once on that account.

As to the peacock, it is excused on the pleas (1), that the individuals maintained are so few in number, and (2), that its beauty is so great it can hardly be improved. But the individuals maintained have not been too few for the independent origin of the black-shouldered form, or for the supplanting of the commoner one by it. As to any neglect in selection, it can hardly be imagined that with regard to this bird (kept as it is all but exclusively for its beauty), any spontaneous beautiful variation in colour or form would have been neglected. On the contrary, it

would have been seized upon with avidity and preserved with anxious care. Yet apart from the black-shouldered and white varieties, no tendency to change has been known to show itself. As to its being too beautiful for improvement, that is a proposition which can hardly be maintained. Many consider the Javan bird much handsomer than the common peacock, and it would be easy to suggest a score of improvements as regards either species.

The guinea-fowl is excused, as being "no general favourite, and scarcely more common than the peacock; but Mr. Darwin himself shows and admits that it is a noteworthy instance of constancy under very varied conditions.

These instances alone (and there are yet others) seem sufficient to establish the assertion that degree of change is different in different domestic animals. It is, then, somewhat unwarrantable in any Darwinian to assume that

all wild animals have a capacity for change similar to that existing in some of the domestic ones. It seems more reasonable to maintain the opposite, namely, that if, as Mr. Darwin says, the capacity for change is different in different domestic animals, it must surely be limited in those domestic animals which have it least, and a fortiori limited in wild animals.

Indeed, it cannot be reasonably maintained that wild species certainly vary as much as do domestic races; it is possible that they may do so, but at least this has not been yet shown. Indeed, the much greater degree of variation amongst domestic animals than amongst wild ones is asserted over and over again by Mr. Darwin, and his assertions are supported by an overwhelming mass of facts and instances.

Of course, it may be maintained that a tendency to indefinite change exists in all cases, and that it is only the circumstances and conditions of life which modify the effects of this tendency to change so as to produce such different results in different cases. But assertion is not proof, and this assertion has not been proved. Indeed, it may be equally asserted (and the statement is more consonant with some of the facts given), that domestication in certain animals induces and occasions a capacity for change which is wanting in wild animals the introduction of new causes occasioning new effects. For, though a certain degree of variability (normally, in all probability, only oscillation) exists in all organisms, yet domestic ones are exposed to new and different causes of variability, resulting in such striking divergencies as have been observed. Not even in this latter case, however, is it necessary to believe that the variability is indefinite, but only that the small oscillations become in certain instances intensified into