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want and ugliness. In other parts of the island, where the population has never undergone the influence of the same causes of physical degradation, it is well known that the same race furnishes the most perfect specimens of human beauty and vigour, both mental and bodily.'
18. Mr. Darwin's doctrine of successive accumulation is a marvellous stretch of that imaginative faculty which sits better on poets than on naturalists. It has been remarked that he "makes at any time but little use of the verb 'to prove' in any of its inflections," habitually preferring "I am convinced," "I believe." 23 Nowhere is this more manifest than in the failure to explain how one minute hypothetical acquisition in an individual animal is to survive undiluted through a thousand generations, to serve as a basis for the next. This is like saying that every specially tall, or specially gifted man, may expect on that account to confer on the indefinitely distant future a race of Shakespeares, or of giants fifty feet high. No such law of entail is seen anywhere in nature. Talk as we will of "elective affinities," the tall and the small among them restore the average, whether in physique or in intelligence. On a lesser scale, it is up to-day and down to-morrow, in the world of beasts as in the world of men.
19. Species, in its stubborn resistance to suppression -its existence as a fact in nature, and not merely as a classifying principle in the human mind-is no small trouble to Mr. Darwin. The discrimination of species resolves itself into three tests-diagnosis of Habitat, Structure, and Procreative Power. These tests may be styled respectively the aboriginal, the anatomical, and the physiological. Two living creatures, one in Jupiter, the other on the earth, cannot possibly be of the same species; and a like criterion may sometimes be applied to forms of life, separated by impassable barriers, at different points of the earth's surface-e. g. the eyeless beetles of Hungary and North America. 24 This is the test of Habitat. Next, anatomically, a species is that which presents to educated inspection certain decisive specialities of structure, dorsal, dental, digital, or functional, such as obviously seclude the form in which they unite from other forms in which they are wanting; constant characters which, in like colligation, are at once common to a certain group of animals, and peculiar to that group-found in all animals of that group, and found in no animal of any other. Lastly, there is the test of Reproductive Power. This depends on the axiom that animals incapable of common off
spring cannot have sprung from common ancestors. While mere varieties, as superficial excursions from type are technically termed, are never mutually infertile, 25 animals of different species are physiologically contrasted with such varieties by reciprocal repugnance or punitive sterility. The mastiff and the terrier freely inter-breed; not so the horse and the ass: the mongrel dog is a parent; the hybrid mule is not. Putting aside. the test of Habitat, we may say broadly, then, that the naturalness of the ultimate grouping of animals is proved by the coincidence of the morphological with the procreative test. Given mutual resemblance (whence species) in anatomical structure, there is also partnership in procreative power; given procreative power (whence genus) there is along with this fidelity to anatomical structure. 26 The application of these tests requires knowledge and care; and Mr. Darwin has dealt. to species-mongers a just rebuke.27 But the Linnæan maxim-Species naturæ opus-rests on foundations too broad and deep to be shaken by casual excess of statement or semblance of perplexity. This Mr. Darwin cannot help feeling to be a stumbling-block, on his ability to remove which the fate of his hypothesis depends. His first, and by far least formidable, task is
to find fertile hybrids. Great naturalists have maintained that none such can be found; but Cuvier declined to commit himself to this assertion. That all varieties are mutually fertile was clear; that almost all species are mutually sterile, if not in the first in the second degree, was clear also. Whether there were exceptions to this seemingly universal rule remained to be seen. Mr. Darwin, however, has found none. "It
is difficult," he admits, "perhaps impossible, to bring forward one case of the hybrid offspring of two animals clearly distinct, being themselves perfectly fertile." And again, "I doubt whether any case of a perfectly fertile hybrid animal can be considered as thoroughly well authenticated." 28 Should it ever be so authenticated, the result would be the establishment of an exception to an all but unrelaxing rule, and the failure in that particular case of a test all but universally available. Other tests might indeed remain. If a wolf-like animal from Jupiter were to inter-breed with a dog-like animal from Saturn, and produce a fertile hybrid race, it would not follow that the two parents had sprung from one stock. Our author's account of his poor success in this first and easiest of his quests may prepare us however for a still more signal failure in that far less hopeful
quest which is vital to his main doctrine. No trace, none, of infertile varieties. The boundary line will not shift; species stands forth an inflexible frontier which. no manipulation can "rectify." A prolific mule remains, as of old, a peg on which to hang a proverb for an impossibility; 29 nor will pouter and fan-tail, by refusing to breed, disown their common pigeonhood. The veto neither slackens nor spreads; nature keeps to her code of prohibited degrees, neither relaxing nor extending them. So huge is the difficulty that it earns for Mr. Darwin the special condolence of the Westminster Review. There is comfort, to be sure, and somewhat of compensation, in the thought that the ape is nearer man than the ape-like lemur is to the ape; but there is sadness, nevertheless, in the constrained confession that the facts of animal fertility and infertility cannot as yet be made to square with Mr. Darwin's scheme, or allow it to take rank as "the theory of species."30 So these gentlemen are meanwhile in the plight of that brace of philosophers, one of whom devoted his energies to the milking of a he-goat, while the other-held the pail.
20. As matters stand, then, the horse, e. g. no more. explains the origin of its near congener the ass, than either would explain an equine quadruped in Mars