Darwin now examined the question whether there were not in nature causes—which without the conscious intention of the breeder—might in the course of time, by means of heredity, produce changes in the living animal analogous to those produced by scientific breeding. These causes he found in the disproportion between the enormous number of germs made by nature and the small number of beings which actually come to maturity. But as the germ struggles for its own development there is of necessity a consequent struggle for existence, which not only shows itself directly in the wear and tear of the body, but also as a struggle for space and light, as in the case of plants. And it is evident that in this fight those individuals have the best prospect of coming to maturity and reproducing themselves which possess certain qualities, perhaps insignificant, but advantageous in their fight for existence. There is a tendency towards the inheritance of these individual properties, and if they occur in several individuals of the same species towards development in the direction once taken, by virtue of the accumulated heredity, while the individuals which are not possessed of these qualities succumb more easily and little by little disappear in the struggle for existence. Thus a species naturally changes by the survival of the fittest.
Against this theory of Darwin Herr Duehring urges that the origin of the idea of the struggle for existence is, as Darwin himself confessed, based on the views of the political economist and theorist, Malthus, on the population question, and he covers it with all the abuse appropriate to the clerical Malthusian views on keeping down the population. Now it happens that Darwin never said that the cause of the struggle for existence theory was to be sought from Malthus. He only said that his theories respecting the struggle for existence are the theories of Malthus applied to the entire vegetable and animal world. How great a blunder Darwin made when he so naively accepted the teachings of Malthus without examination may be seen from the fact that there is no need to employ the spectacles of Malthus in order to detect the struggle for existence in nature,—the contradiction between the innumerable mass of germs which nature produces in such prodigality and the slight number which can manage to reach maturity, a contradiction which resolves itself into an apparently grim fight for existence. And with regard to the law of wages the Malthusian doctrines are widely advertised and Ricardo based his contentions upon them,—so the struggle for existence in nature may find a standing even without the Malthusian interpretation. Besides the organisms of nature have their law of population, the establishment of which would decide the theories of the development of species. And who gave the decisive impetus in that direction? Nobody but Darwin.
Herr Duehring is on his guard against entering upon the positive side of this question. Instead he must again find fault with the struggle for existence. There can be no argument about a struggle for existence between plants and the genial eaters of plants "in a sufficiently accurate sense the struggle for existence only occurs within the sphere of brutality, in so far as nourishment depends upon robbery and consumption." And after he has reduced the concept struggle for existence to these narrow limits he gives his wrath free play as regards the brutality of this conception which he himself has narrowed down to a brutal conception. But this moral wrath simply reacts on Herr Duehring himself, the inventor of this sort of struggle for existence. It is not Darwin therefore who seeks among the lower animals the "conditions of the operations of nature" (as a matter of fact Darwin would have included the whole of organic nature in the struggle), but one of Herr Duehring's bugaboos. The expression "struggle for existence" in particular excites Herr Duehring's lofty moral scorn. That this actually exists among plants every meadow, every cornfield and every wood can show him. We need not trouble about the name, whether one call it "struggle for existence" or "lack of the conditions of existence and want of mechanical realisation," but as to how this fact operates as regards the maintenance or transformation of species. With regard to this Herr Duehring persists in a characteristically stubborn silence. We cannot trouble ourselves any more about natural selection.
But "Darwinism produces its changes and differentiations out of nothing." Darwin thoroughly understands that he is engaged with the causes which have produced changes in individuals and in the second place he is engaged with the mode in which such individual differentiations tend to mark off a race, a genus, or a species. Darwin moreover was less occupied in discovering these causes, which up to the present are either entirely unknown or on which there is only general information, than in discovering a rational form in which to establish their reality, to embrace their permanent significance. But Darwin ascribed too wide a reach to his discovery in this that he made it an exclusive means of variation in species and neglected the causes of individual differentiations from the general form. This mistake however is common to most people who make a step forwards. Next, if Darwin produces his changes in individual types out of nothing and thereby excludes the wisdom of the breeder, the breeder on his part must not only display his wisdom but he must produce out of nothing real changes in plant and animal forms. But who has given the impetus to the investigation as to whence these variations and differentiations proceed? It is again no one but Darwin.
Lately the conception of natural selection has been broadened, by Haeckel, in particular, and the variation of species has been shown to be the result of actual change owing to adaptation and inheritance, whereby adaptation is considered as the source of variations and heredity as the conserving element in the process. Even this is not correct in Herr Duehring's eyes. "Peculiar adaptation to the circumstances of life as they are offered or withheld by nature supposes impulses and facts which answer to the conception. Hence adaptation is only apparent and actual causality does not elevate itself above the lowest steps of physical, chemical and plant physiology." It is again the name which provokes Herr Duehring. But how does he deal with the matter? The question is if such changes do take place in the species of organic beings or not. And again Herr Duehring has no reply.
"If a plant in the course of its growth takes a direction by which it gets the most light the result is nothing but a combination of physical forces and chemical agents, and if we are to call it an adaptation, not metaphorically but strictly, confusion is certain to arise in the motion." This man is so exacting with other people because he is quite well acquainted with the intentions of nature and speaks of the subtlety of nature, even of its will. There is confusion, indeed, but with whom, with Haeckel or with Herr Duehring?
And the confusion is not only spiritual but logical. We have seen that Herr Duehring put forth all his efforts to make the purpose idea in nature real. "The relation of means and end does not by any means show a conscious intention." But what is adaptation without conscious intention, without any intrusion of design of which he complains so loudly, but an unconscious teleology?
If the color of tree frogs and leaf eating insects is as a rule green and that of beasts that inhabit the desert sandy-yellow, and that of polar animals white, they have certainly not come into possession of this coloring intentionally or through any kind of mental process, on the contrary the coloring can only be explained by means of the operation of physical substances and chemical agents. And yet it cannot be denied that by these colors these animals are particularly adapted to the conditions in which they are and it is certain that they are by their means rendered less visible to their enemies. Just of a similar nature are the organs by which certain plants seize and consume certain insects (the means being on their under side, suited to this purpose and adapted to this end). Now if Herr Duehring insists that the adaptation must be realised through the operation of thought, he only says that the purpose must be carried out through mental operation, must be conscious and intentional. Thus again, just as in the philosophy of realism we arrive at the Creator with a purpose, at God. Formerly this kind of declaration was called "deism" and Herr Duehring says that we had not much regard for it, but it now appears that the world has gone backwards in this respect also.
From adaptation we come to heredity and here according to Herr Duehring Darwinism is quite out. "The whole organic world, Darwin explained, came from a single germ, is, so to speak, the brood of a single being. Independent similar products of nature according to Darwin do not exist without heredity and his retrogressive philosophy must come to a full stop when the end of the thread of ancestry is reached, or the original vegetable form."
The statement that Darwin traced all existing organisms from one original germ is to put it politely a piece of pure imagination on the part of Herr Duehring. Darwin says distinctly on the last page of the Origin of Species, Sixth Edition, that he regards all living beings not as separate creations but as the descendants in a direct line from some fewer beings and Haeckel makes a distinct advance on this ascribes "an entirely distinct source for plants and another for the animal kingdom" and on and between both of them "a number of original stems each of which has developed independently from one single primary monistic form." (History of Creation page 397.) This original form of life Herr Duehring discovers solely to bring it into contempt by paralleling it with the first man according to Jewish tradition, Adam. Here, unfortunately for Herr Duehring, he does not know how this original Jew turns out, according to Smith's Assyrian discoveries to have been the original Semite, and that the entire Biblical story of the Creation and the Flood has been shown to have been taken from a legendary store common to the Jews, Babylonians, Chaldeans, and Assyrians.