In all the discussions on close interbreeding, no case meets with such frequent mention as that of the pig. Those who endeavor to gainsay the conclusion that evil is attendant on in-and-in breeding, signally fail to invalidate the fact that pigs die out altogether after being bred in-and-in for several generations. Those persons are the exceptions, however, who consider the fact as questionable. On page 121, vol. ii., Darwin says, "With pigs there is more unanimity among breeders on the evil effects of close interbreeding than, perhaps, with any other large animal." He then gives quite a number of facts, which we will not quote, as they are indisputable.
Close interbreeding being attended, in pigs, by evil effects is, at first sight, at variance with our doctrine. For, not only does utility guide the selection of pigs, but they are, as Darwin has informed us, the most striking instance of convergence of character. We have seen the greatest evil effects of in-and-in breeding in those species in which selection is guided by fancy, and of which the varieties were the most divergent in character. A superficial consideration, then, would lead one to expect that, where the converse obtained—where utility was the motive in selection, and where the varieties were convergent in character—interbreeding would entail little or no evil effects. But the incongruity between the facts and the doctrine is only apparent, not real. There is presence of evil effects, because, in this case, the motive of utility and convergence of character also involve disproportionate development. Disproportionate development is the only never-failing criterion. In our last article we showed that, while divergence of character is solely caused by disproportionate development, convergence of character may be induced by either proportionate or disproportionate development. We further showed that the pig's convergence of character is caused by disproportionate development, and that the pig has many characters either wholly or partially suppressed. Its coat of bristles is greatly diminished, and its tusks are wholly reduced. Owing to a misguided policy, its legs are of the smallest possible size, and, by correlation, the front of the head is remarkably short and concave. Being, then, thus disproportionately developed, the pig, of all large animals, must be, upon our doctrine, the most susceptible of evil from close interbreeding. Allow the legs to be of proportionate size, and a marked decrease in the evil entailed by interbreeding will be observable. So impressed are we with the idea of the truth of our doctrine, that we will stake its validity upon the result, confident that, in doing so, we venture nothing.
That the cause assigned for the lessened fertility and delicacy of constitution of pigs is a true one, is placed beyond all doubt by the fact that, with those members of the species of which but little care is taken, there is comparatively very little evil entailed by close interbreeding. The reason lies in the circumstance that, in these animals, the legs are far more proportionately developed than in well-bred pigs; and that there is absent the shortness and concavity of the front of the head. The more well-bred the animals, the greater are the injurious effects of in-and-in breeding. This fact needs not proof; it is too well known. Care in breeding pigs almost invariably induces the small development of the legs and of the front of the head. A case somewhat analogous is presented by the fowl and pigeon. With them, the more careful the selection, the greater are the evil effects of interbreeding. With cattle, sheep, and horses, however, good breeding is a condition sine qua non of their exemption from the evil generally consequent on close interbreeding. Why care should be attended by different results in different species, is at first not clear. But this is the explanation. In fowls and pigeons, care in the formation of varieties induces greater disproportionate development by augmenting the divergence of character. In cattle, sheep, and horses, on the contrary, care, by inducing greater convergence, causes increased proportionate development. This convergence, be it remembered, is attributable to a cause other than that which creates the convergence of character of the breeds of well-bred pigs.
We incline to believe that the extremely small amount of evil attendant on reduced size never manifests itself by close interbreeding. That some evil, though inappreciably small, does result from reduced size, may reasonably be inferred from the fact that, where animals disproportionately developed are crossed, increase in size follows, and that, where those animals are closely interbred, decrease in size results.
We are assured that there are cases in which crossing, instead of resulting in good, induces evil effects. Darwin says he has not met with any well-established case, with animals, in which this occurs. Now, our theory contemplates such evil effects under the following circumstances. The varieties crossed must each be distinguished from other varieties by a negative feature. In addition to this, they must lack features in common. The evil resulting would then be attributable to the same cause which induces the evil consequent on close interbreeding.
It is now clear that these phenomena of crossing and close interbreeding tell a tale the direct converse and refutation of that which Darwin would have us believe. They are manifestly, grossly, absolutely, and irreconcilably at variance with the doctrine of evolution. They show conclusively that no divergence of character is normally possible; that all the characters of the species are alone susceptible of perfect coördination; that the exclusive possession of any positive character by any variety is to the detriment of the other varieties; that the possession of any negative feature is deleterious to the organism; and that there can normally exist but one variety—the perfect type, that variety in which all the positive features are fully and proportionately developed. These conclusions cannot be gainsaid; for they irresistibly force themselves upon one by observation of the phenomena of crossing and close interbreeding, furnished by Darwin.
We have now propounded a counter-theory and a refutation of Darwinism. In doing so, we have introduced no new factors. We have used only those with which Darwin has furnished us. There are, however, three factors recognized by Darwin which we have eliminated. These are an innate tendency in organisms to vary, evolution, and the law of compensation of growth. Of these, the first is confessedly unscientific; the second, irrespective of the well-founded doubt as to whether it obtains or not, must share in the same discredit which is accorded to the first; and the third is viewed with distrust even by Darwin himself. The factors, however, which we have retained must be conceded to be immeasurably more amenable to the canons of scientific research, upon the theory of reversion, than when they are adduced to subserve the hypothesis of evolution. In our treatment of them they have fulfilled the highest requirements of logic. Take, for example, the four principal laws involved in the controversy—variation, correlation, crossing, and close interbreeding. These we found ultimate or empirical laws, and left them derivative laws. The law of variation we resolved into the law of reversion; and the laws of correlation, crossing, and close interbreeding we resolved into the law of proportionate development. Now, it is not possible for a theory to be capable of all this, and yet to be false. If the laws upon which we based our theory were merely empirical, a doubt of its validity might reasonably be entertained. But, as the case stands, it cannot.
But—may exclaim a tyro who affects a love for science, and whose conception of biology is limited to protoplasm and cells—assuming that the hypothesis of reversion is vastly more conformable to the phenomena of variation than the hypothesis of evolution, yet your theory fails to supply the greatest requirement of biologic science. It fails to satisfy our yearnings after a knowledge of the development of the species. Darwin starts with cells, the lowest congregations of organic matter. Because he does this his theory is, at least philosophically, the more scientific.
But, even in this respect, our theory is more philosophical than that of Darwin. Darwin assumes three or four cells, and intrusts spontaneity or chance with the development of the species. We assume, not "a myriad supernatural impulses" going to the formation of each species, not the creation of each species in its maturity, but one cell alone for each species, (or, perhaps, one cell for each sex of each species.) For evidence of the fact that the assumption of a multiplicity of cells is more philosophical than the assumption of only three or four, we appeal to an article in the North American Review for October, 1868, entitled "Philosophical Biology," of which the writer is a professed Darwinian, and to G. H. Lewes's articles in the Fortnightly Review. Given, then, these cells, we intrust the development of the species, not to spontaneity or chance, but to the operation of laws similar to those obtaining in the crystal. The forces implied in the creation, formation, or existence of each cell determine, as in the case of the crystal, the whole form and structure of the species. The process of development is that predetermined, from which no departure is normally possible. Time, however, is an unimportant element. This kind of evolution of the species we concede. That which we deny is the evolution of the species one from another.
In conclusion, we cannot refrain from stating that our views are quite consistent with a high admiration of the great ingenuity and vast research displayed by Mr. Darwin. His desire to be frank and candid none can gainsay. For the ability of Mr. Spencer, who is somewhat less candid, but immeasurably more so than the petty retailers of his conceptions, we have the deepest respect. His exquisitely constructed mind we ever delight to study. Both Mr. Darwin and Mr. Spencer have rendered great services to the cause of science. And we must in candor admit that the British "infidels" generally present their theories in a form which admits of their eventual confirmation, or their eventual refutation. As we are confident that their refutation will follow whenever they are really at variance with religion, we anticipate with pleasure many a warm but amicable controversy within the next half-century.