On the other hand, we must not take our idea of tameness merely from the domesticated animals. These have been bred for many generations, and those that were most wild and that showed any resistance to man were killed or allowed to escape. Dogs are always taken as the supreme example of tameness, and sentimentalists have almost exhausted the resources of language in praising them. Like most people, I am very fond of dogs, but it is an affection without respect. Dogs breed freely in captivity, and in the enormous period of time that has elapsed since the first hunters adopted wild puppies there has been a constant selection by man, and every dog that showed any independence of spirit has been killed off. Man has tried to produce a purely subservient creature, and has succeeded in his task. No doubt a dog is faithful and affectionate, but he would be shot or drowned or ordered to be destroyed by the local magistrate if he were otherwise. A small vestige of the original spirit has been left in him, merely from the ambition of his owners to possess an animal that will not bite them, but will bite anyone else. And even this watch-dog trait is mechanical, for the guardian of the house will worry the harmless, necessary postman, and welcome the bold burglar with fawning delight. The dog is a slave, and the crowning evidence of his docility, that he will fawn on the person who has beaten him, is the result of his character having been bred out of him. The dog is an engaging companion, an animated toy more diverting than the cleverest piece of clockwork, but it is only our colossal vanity that makes us take credit for the affection and faithfulness of our own particular animal. The poor beast cannot help it; all else has been bred out of him generations ago.
When wild animals become tame, they are really extending or transferring to human beings the confidence and affection they naturally give their mothers, and this view will be found to explain more facts about tameness than any other. Every creature that would naturally enjoy maternal, or it would be better to say parental, care, as the father sometimes shares in or takes upon himself the duty of guarding the young, is ready to transfer its devotion to other animals or to human beings, if the way be made easy for it, and if it be treated without too great violation of its natural instincts. The capacity to be tamed is greatest in those animals that remain longest with their parents and that are most intimately associated with them. The capacity to learn new habits is greatest in those animals which naturally learn most from their parents, and in which the period of youth is not merely a period of growing, a period of the awakening of instincts, but a time in which a real education takes place. These capacities of being tamed and of learning new habits are greater in the higher mammals than in the lower mammals, in mammals than in birds, and in birds than in reptiles. They are very much greater in very young animals, where dependence on the parents is greatest, than in older animals, and they gradually fade away as the animal grows up, and are least of all in fully grown and independent creatures of high intelligence.
Young animals born in captivity are no more easy to tame than those which have been taken from the mother in her native haunts. If they remain with the mother, they very often grow up even shyer and more intolerant of man than the mothers themselves. There is no inherited docility or tameness, and a general survey of the facts fully bears out my belief that the process of taming is almost entirely a transference to human beings of the confidence and affection that a young animal would naturally give its mother. The process of domestication is different, and requires breeding a race of animals in captivity for many generations and gradually weeding out those in which youthful tameness is replaced by the wild instinct of adult life, and so creating a strain with new and abnormal instincts.
B. PLANT COMMUNITIES AND ANIMAL SOCIETIES
1. Plant Communities[84]
Certain species group themselves into natural associations, that is to say, into communities which we meet with more or less frequently and which exhibit the same combination of growth-forms and the same facies. As examples in northern Europe may be cited a meadow with its grasses and perennial herbs, or a beech forest with its beech trees and all the species usually accompanying these. Species that form a community must either practice the same economy, making approximately the same demands on its environment (as regards nourishment, light, moisture, and so forth), or one species present must be dependent for its existence upon another species, sometimes to such an extent that the latter provides it with what is necessary or even best suited to it (Oxalis Acetosella and saprophytes which profit from the shade of the beech and from its humus soil); a kind of symbiosis seems to prevail between such species. In fact, one often finds, as in beech forests, that the plants growing under the shade and protection of other species, and belonging to the most diverse families, assume growth-forms that are very similar to one another, but essentially different from those of the forest trees, which, in their turn, often agree with one another.
The ecological analysis of a plant-community leads to the recognition of the growth-forms composing it as its ultimate units. From what has just been said in regard to growth-forms it follows that species of very diverse physiognomy can very easily occur together in the same natural community. But beyond this, as already indicated, species differing widely, not only in physiognomy but also in their whole economy, may be associated. We may therefore expect to find both great variety of form and complexity of interrelations among the species composing a natural community; as an example we may cite the richest of all types of communities—the tropical rain-forest. It may also be noted that the physiognomy of a community is not necessarily the same at all times of the year, the distinction sometimes being caused by a rotation of species.
The different communities, it need hardly be stated, are scarcely ever sharply marked off from one another. Just as soil, moisture, and other external conditions are connected by the most gradual transitions, so likewise are the plant-communities, especially in cultivated lands. In addition, the same species often occur in several widely different communities; for example, Linnaea borealis grows not only in coniferous forests, but also in birch woods, and even high above the tree limit on the mountains of Norway and on the fell-fields of Greenland. It appears that different combinations of external factors can replace one another and bring into existence approximately the same community, or at least can satisfy equally well one and the same species, and that, for instance, a moist climate often completely replaces the forest shade of dry climates.
The term "community" implies a diversity but at the same time a certain organized uniformity in the units. The units are the many individual plants that occur in every community, whether this be a beech forest, a meadow, or a heath. Uniformity is established when certain atmospheric, terrestrial, and other factors are co-operative, and appears either because a certain defined economy makes its impress on the community as a whole, or because a number of different growth-forms are combined to form a single aggregate which has a definite and constant guise.
The analysis of a plant-community usually reveals one or more of the kinds of symbiosis as illustrated by parasites, saprophytes, epiphytes, and the like. There is scarce a forest or a bushland where examples of these forms of symbiosis are lacking; if, for instance, we investigate the tropical rain-forest we are certain to find in it all conceivable kinds of symbiosis. But the majority of individuals of a plant-community are linked by bonds other than those mentioned—bonds that are best described as commensal. The term commensalism is due to Van Beneden, who wrote, "Le commensal est simplement un compagnon de table"; but we employ it in a somewhat different sense to denote the relationship subsisting between species which share with one another the supply of food-material contained in soil and air, and thus feed at the same table.