On page 61, Vol. II., he says, "It is probable that hardly a change of any kind affects either parent without some mark being left on the germ. But on the doctrine of reversion, as given in this chapter, the germ becomes a far more marvellous object; for besides the visible changes to which it is subjected, we must believe that it is crowded with invisible characters, proper to both sexes, to both the right and left side of the body, and to a long line of male and female ancestors, separated by hundreds or even thousands of generations from the present time; and these characters, like those written on paper with invisible ink, all lie ready to be evolved (!!!) under certain known or unknown conditions." If this is the case, is not the scope of reversion sufficiently wide to cover every favorable modification which has arisen, or may arise, under domestication?
But these extracts from Darwin's Animals and Plants under Domestication, strongly confirmatory as they are of our hypothesis, ill sustain a comparison with the last we shall adduce. Fuller concession no one could reasonably desire.
"With species in a state of nature," says Darwin, on page 317, "rudimentary organs are so extremely common that scarcely one can be mentioned which is wholly free from a blemish of this nature." Stronger confirmation of our hypothesis, short of a full and unequivocal confession of its validity, we are utterly unable to conceive. Are we not, after this, justified in ascribing to reversion every favorable modification which has arisen or may arise?
Having thus furnished full warrant for assuming degeneration and subsequent favorable reversion, and for alleging the complete gratuitousness of the converse assumption of evolution, let us turn our attention to the grand principle of natural selection.
It is scarcely possible to read Darwin's graphic description of the struggle for existence among animals and plants, and not marvel at their survival. Creatures under nature are subjected to the greatest vicissitudes of climate. Thousands are born into the world with delicate constitutions, inherited from their progenitors. These enter into competition with their fellows for the means of subsistence; and although they eventually succumb, they have, during their short lives, by this competition, induced the deterioration of their stronger companions. All without exception have to struggle, from the hour of their birth to the hour of their death, for existence. Natural extinction carries off those whose impaired constitutions are inconsistent with prolonged existence. Consequent upon natural extinction is the survival of the fittest and strongest. Darwin avers that the weaker portion of the species having been carried off by natural extinction, the next generation, having been derived only from the stronger portion of the race, will be of a still stronger constitution. This is not the case. Natural extinction does not arbitrarily carry off the weak, but merely those whose extremely impaired constitutions are incompatible with life. Many survive between which and the conditions there is little compatibility. And even the offspring of those which are the strongest are subjected in their turn to the same if not worse conditions, and to the same if not severer competition; for the probability is, that the increase in the number of animals and plants has been great. Thus degeneration is ever active. If the climate fails to entail deterioration, and becomes favorable, the same result is produced by the severe competition consequent upon "an astonishingly rapid increase in numbers."
Darwin implies that natural selection is something more than the correlative of natural extinction. That it is, he has not shown. All the facts show that the one is merely the correlative of the other. The semblance of the converse being the case is given, we conceive, by the constant use, when speaking of those preserved by natural selection, of the superlative, as strongest, fittest, most vigorous. Under nature, unfavorable modifications are ever arising, and those animals and plants which possess them in a marked degree are carried off by natural extinction. Natural selection, in its turn, operates merely by the preservation of those organisms which have undergone little or no modification. The two factors are only different aspects of the same process. One necessitates the other. More than this, natural selection is not. That it acts by the preservation of successive favorable modifications, Darwin has signally failed to adduce a single instance to prove. Instances of adaptation he has adduced, but they are invariably, except where man has intervened, those of degeneration. A description of the process of natural selection is always accompanied with an account of the incessant war waging throughout nature, resulting in natural extinction. Following this is natural selection, preserving the fitter, stronger, and more vigorous. Now, a tolerably clear conception of our view may be gained by considering that, although those preserved may be the fitter, stronger, and more vigorous, in comparison with their brothers or contemporaries, they may be—and the vast majority of the instances adduced by Darwin show this to be the case—less fit, less strong, and less vigorous than their progenitors. Those instances adduced which do not imply this, show no advance on the progenitors, but merely a struggle against degeneration and a continuance in the same state. For animals and plants under nature can scarcely hold their own. Many of them are reduced to the lowest condition compatible with life. If they do not remain stationary, their movement is in the direction of degeneration. Does not Darwin's assertion, before adverted to, that rudimentary organs are so extremely common that scarcely a single species can be mentioned which does not possess such a blemish, imply the preëxistence of conditions sufficiently adverse to entail unfavorable changes in almost every point or character in an organism? It is not a little amusing to see that, in numbers of the exemplifications of the process of natural selection given by Darwin, the animals and plants are subjected to extreme vicissitudes of climate, the severest competition, and other unfavorably modifying influences, and although deterioration is acknowledged to result, and it is manifest that all are unfavorably modified, he invariably concludes with the assertion that the strongest and most vigorous survive. This assertion is true in one sense, but is false when viewed with reference to the inference intended to be drawn. It will be seen that the more correct assertion would be, those survive which have undergone less modification or none.
But independently of these considerations; even upon the supposition that natural selection was equally powerful with man's selection in the formation of varieties or races, that as strongly pronounced and as widely divergent modifications as those observable under domestication had arisen under nature, the efficiency of natural selection is a matter of no moment. For the argument therefrom begs the whole question. It takes for granted the whole point really in controversy. It assumes that those modifications which may arise, or which have arisen, are due to evolution. It is not in the least inconsistent with our views that favorable varieties or races should arise under nature. As a matter of fact, we deny their ever having arisen. But we are not by this denial estopped from believing it possible for them to arise in the future. For were the conditions to change, and to become as favorable as those to which animals and plants are subjected under domestication, races would then arise. They would probably be fewer in number, but a nearer approach to perfection could be attained, the conditions admitting; for man's improvement of the animals and plants under his care is retarded, owing to his not being as yet perfectly conversant with the conditions requisite for their full development. But the modifications which may arise under nature will be due to reversion. The improvement of natural species will imply their previous degeneration. Darwin conceives variations to arise by evolution, and concession of this is essential to the validity of his argument. The question then recurs, Are the favorable modifications which have arisen, or which may arise, due to evolution or to reversion? Until this point is settled in favor of the ascription to evolution, Darwin's argument from natural selection is wholly irrelevant.
An illustration may perhaps conduce to a clearer conception of the relation in which the theories of evolution and reversion stand to each other. The following will, we believe, fully serve this purpose.
Conceive a glass tube, bent into the shape of the letter V, of which the left leg alone is clearly visible. In this, water is seen slowly ascending by a succession of apparently spontaneous impulses. "Now," argue a certain class of philosophers, "this is a peculiar case. The water here manifestly does not acknowledge the law of gravitation. It must, then, conform to a law sui generis; a law of which we are wholly ignorant; a law which transcends the scope of our intelligence. This law, be it what it may, we will term evolution. Now, as this name, given arbitrarily, is the only explanation of which the singular ascent of the water will admit, we are forced to conclude that the water will, if similarly confined above as here below, continue to rise for ever. Any theory other than this is inconceivable. The assumption of a limit to the ascent of the water is manifestly wholly gratuitous. What evidence is there to induce the belief that there exists such a limit?" But would not the calculations of these philosophers be signally confounded by the removal of the covering of the right leg of the tube, disclosing the downward course of the water from a certain height? The analogy, we presume, is clear to all. The ascent of the water in the left leg answers to the appearance of the profitable modifications under domestication, the apex of the tube to the existing state of nature, and the descent of the water in the right leg answers to degeneration under nature; while the height from which the water has descended in the right leg, and to which in the left leg it is ascending in conformity to the rule that water always seeks its own level, in like manner answers to the perfect type of the species from which the animal or plant has degenerated, and to which it is reverting.
But, even assuming that the argument from the gratuitousness of the assumption of varietal evolution, together with that from the explanation afforded by the theory of reversion, is inconclusive, there is yet another which may be adduced.