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Permitted perturbation is kept in check by the over-ruling law of equilibrium and recovery. Man's experiments on the lower creatures, then, so far from yielding an analogy to the methods of nature, present the strongest possible contrast.
It is by suspending and crossing those methods that such experiments succeed. Man is a reformer, often a deformer,
, and his influence over animals is innovation ; it is the
l sole aim of nature to keep them up to the mark. She may be repulsed or counteracted, tamen usque recurret. We talk of the “unchanging east.” Nature, save by the Creative will and interference, is more changeless than the unchanging east of man.
17. If we must apply the same name, then, to quite distinct and antagonistic processes, let it not be forgotten that natural “ selection” is ever tending to efface such exceptional peculiarities in animal structure as human selection strives to cherish and perpetuate. All variation, moreover, howsoever brought about, is transacted within inflexible limits. Let the “ magician's wand” be waved ever su dexterously, a sheep is still a sheep. In six years, we are assured, 21 Sir John Sebright will undertake to modify to pattern the head and beak of a pigeon : in how many more will he engage to turn the
milk which it is the wonderful prerogative of this family to secrete in the “crop,” during the breeding season, for after mixture with the food of its young, into mammalian channels? For be it likewise carefully noted that such variation as is proved to be attainable, whether through human experiments, or under changed outward conditions, is not of the nature of ascensive development. To alter is not necessarily to elevate. To cultivate one point in an animal artificially, is to sacrifice another; and what the breeder calls “improvement” the naturalist deems deformity. Adaptive diversity may depress below the old level, but it will not promote to a new.
At best it imports a power of conforming without injury to altered circumstances; but much more frequently degradation under hardships. Take the most decisive of examples, that of man himself. No conceivable change in food or climate will materially improve a robust and well-fed race. On the other hand, stinted food brings stunted stature. In Sligo and northern Mayo ;—“Five feet two inches upon an average, pot-bellied, bow-legged, abortively featured, their clothing a wisp of rags ; these spectres of a people that two centuries ago were wellgrown, able-bodied and comely, stalk abroad into the daylight of civilization, the annual apparitions of Irish
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." 22
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
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 offspring 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
1 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 naturce 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