Morality, whether we take it in the narrower or broader sense, can always be traced to the physiological function of adaptation, which is closely connected through nutrition with the self-maintenance of the organism. The change in the plasm which adaptation brings about is always based on the chemical energy of metabolism (chapter ix.). Hence it will be as well to have a clear idea of the nature of adaptation. I defined it as follows in my General Morphology:
Adaptation or variation is a general physiological function of organisms, closely connected with their radical function of nutrition. It expresses itself in the fact that every organism may be modified by the influence of the environment, and may acquire characters which were wanting in its ancestors. The causes of this variability are chiefly found in a material correlation between parts of the organism and the outer world. Variability or adaptability is not, therefore, a special organic function, but depends on the material, physico-chemical process of nutrition.
I have developed this conception of adaptation in the tenth chapter of the History of Creation.
The nature of the adaptation and its relation to variation are often conceived in different ways from that I have defined. Quite recently Ludwig Plate has restricted the idea, and understood by adaptation only variations that are useful to the organism. He severely criticises my broader definition, and calls it "a palpable error," suggesting that I only retain it because I am not open to conviction. If I wanted to return this grave charge, I might point to Plate's one-sided and perverse treatment of my biogenetic law. Instead of doing this I will only observe that I think the restriction of adaptation to useful variations is untenable and misleading. There are in the life of man and of other organisms thousands of habits and instincts that are not useful, but either indifferent or injurious to the organism, yet certainly come under the head of adaptation, are maintained by heredity, and modify the form. We find adaptations of all sorts—partly useful, partly indifferent, partly injurious (the result of education, training, distortion, etc.)—in the life of man, and the domestic animals and plants. I need only refer to the influence of fashion and the school. Even the origin of the useless (and often injurious) rudimentary organs depends on adaptation.
Habit is a second nature, says an old proverb. This is a profound truth, the full appreciation of which came to us through Lamarck's theory of descent. The formation of a habit consists in the frequent repetition of one physiological act, and so is in principle reducible to cumulative or functional adaptation. Through this frequent repetition of one and the same act, which is closely connected with the memory of the plasm, a permanent modification is caused, either in a positive or a negative sense; positively the organ is developed and strengthened by exercise, negatively it is atrophied or enfeebled by disuse. When this accumulation of slight changes continues, the effect of adaptation goes so far in time as to produce new organs by progressive modification, or to cause actual organs to become useless and rudimentary, and finally disappear, owing to regressive metamorphosis.
When we make a careful study of the simpler processes of habit in the lower organisms, we see that they depend, like all other adaptations, on chemical changes in the plasm, and that these are provoked by trophic stimuli—that is to say, by external action on the metabolism. As Ostwald rightly says: "The most important function of organisms is the conversion of the various chemical energies into each other. The chemical energy that is taken into the organism as food is not generally capable of being applied directly to its purposes, but needs some further preparation. Every cell is a chemical laboratory, in which the most varied reactions take place without fires and retorts. The most frequently employed means in this is probably the catalytic acceleration of the usable and the catalytic retardation of the useless reactions. As a proof of this we have the regular presence of these enzyma in all organisms." In this the greatest importance attaches to memory, which I regard with Hering as a general property of living substance, "in virtue of which certain processes in the living being leave effects behind them that facilitate the repetition of the processes." I agree with Ostwald that "the importance of this property cannot be exaggerated. In its more general forms it effects adaptation and heredity, in its highest development the conscious memory." While the latter, and consciousness in general, reach the highest stage in the mental life of civilized man, the adaptation of the monera remains at the lowest stage. Among the latter the bacteria especially, which have assumed the most varied and important relations to other organisms in spite of the simplicity of their structure, show that this manifold adaptation depends on the formation of habits in the plasm, and is solely based on their chemical energy, or their invisible molecular structure. Once more the monera form a connecting link between the organic and inorganic; they fill up the deep gulf, from the point of view of energy, that seems to yawn between "animated" organisms and "lifeless" bodies.
According to the prevailing view, habit is a purely biological process, but there are processes even in inorganic nature which come under this head in the broader sense. Ostwald gives the following illustration:
If we take two equal tubes of thin nitric acid and dissolve a little metallic copper in one of them, the liquid will acquire the power to dissolve a second piece of the same metal more quickly than the one that remains unchanged. The cause of this phenomenon—which may be observed in the same way with mercury or silver and nitric acid—is that the lower oxydes of nitrogen that are formed in dissolving the metal accelerate the action of the nitric acid catalytically on the fresh metal. The same effect is produced if you put part of these oxydes in the acid; it then acts much more rapidly than pure acid. The formation of a habit consists, therefore, in the production of a catalytic acceleration during the reaction.
We may not only compare inorganic habit with organic adaptation, which we call habit or practice, but also with "imitation," which implies a catalytic transfer of habits to socially united living beings.
By instincts were formerly understood, as a rule, the unconscious impulses of animals which led to purposive actions, and it was believed that every species of animal had special instincts implanted in it by the Creator. Animals were thought, according to Descartes's view, to be unconscious machines whose actions proceed with unvarying constancy in the particular form that God had ordained. Although this antiquated theory of instinct is still taught by many dualistic metaphysicians and theologians, it has long since been demolished by the monistic theory of evolution. Lamarck had observed that most instincts are formed by habit and adaptation, and then transmitted by heredity. Darwin and Romanes especially showed afterwards that these inherited habits are subject to the same laws of variation as other physiological functions. However, Weismann has recently taken great pains in his Lectures on the Theory of Descent (xxiii.) to refute this idea, and in general the hypothesis of an inheritance of acquired characters, because it will not harmonize with his theory of the germ-plasm. Ernst Heinrich Ziegler, who has recently (1904) published a subtle analysis of former and present ideas of instinct, agrees with Weismann that "all instincts are due to selection, and that they have their roots not in the practice of the individual life, but in the variations of the germ." But where else can we find the cause of these "germ-variations" except in the laws of direct and indirect adaptation? In my opinion, it is just the reverse; the remarkable phenomena of instinct yield a mass of evidence of progressive heredity, completely in the sense of Lamarck and Darwin.