In neither of the two first cases is there any scope for the idea of purpose; in the third, purpose must be present immediately before the action. In the two first cases, action is supposed to be brought about by means of an initial arrangement, either of bodily or mental mechanism, purpose being conceived of as existing on a single occasion only—that is to say, in the determination of the initial arrangement. In the third, purpose is conceived as present in every individual instance. Let us proceed to the consideration of these three cases.
Instinct is not a mere consequence of bodily organisation; for—
(a.) Bodies may be alike, yet they may be endowed with different instincts.
All spiders have the same spinning apparatus, but one kind weaves radiating webs, another irregular ones, while a third makes none at all, but lives in holes, whose walls it overspins, and whose entrance it closes with a door. Almost all birds have a like organisation for the construction of their nests (a beak and feet), but how infinitely do their nests vary in appearance, mode of construction, attachment to surrounding objects (they stand, are glued on, hang, &c.), selection of site (caves, holes, corners, forks of trees, shrubs, the ground), and excellence of workmanship; how often, too, are they not varied in the species of a single genus, as of parus. Many birds, moreover, build no nest at all. The difference in the songs of birds are in like manner independent of the special construction of their voice apparatus, nor do the modes of nest construction that obtain among ants and bees depend upon their bodily organisation. Organisation, as a general rule, only renders the bird capable of singing, as giving it an apparatus with which to sing at all, but it has nothing to do with the specific character of the execution . . . The nursing, defence, and education of offspring cannot be considered as in any way more dependent upon bodily organisation; nor yet the sites which insects choose for the laying of their eggs; nor, again, the selection of deposits of spawn, of their own species, by male fish for impregnation. The rabbit burrows, the hare does not, though both have the same burrowing apparatus. The hare, however, has less need of a subterranean place of refuge by reason of its greater swiftness. Some birds, with excellent powers of flight, are nevertheless stationary in their habits, as the secretary falcon and certain other birds of prey; while even such moderate fliers as quails are sometimes known to make very distant migrations.
(b.) Like instincts may be found associated with unlike organs.
Birds with and without feet adapted for climbing live in trees; so also do monkeys with and without flexible tails, squirrels, sloths, pumas, &c. Mole-crickets dig with a well-pronounced spade upon their fore-feet, while the burying-beetle does the same thing though it has no special apparatus whatever. The mole conveys its winter provender in pockets, an inch wide, long and half an inch wide within its cheeks; the field-mouse does so without the help of any such contrivance. The migratory instinct displays itself with equal strength in animals of widely different form, by whatever means they may pursue their journey, whether by water, land, or air.
It is clear, therefore, that instinct is in great measure independent of bodily organisation. Granted, indeed, that a certain amount of bodily apparatus is a sine quâ non for any power of execution at all—as, for example, that there would be no ingenious nest without organs more or less adapted for its construction, no spinning of a web without spinning glands—nevertheless, it is impossible to maintain that instinct is a consequence of organisation. The mere existence of the organ does not constitute even the smallest incentive to any corresponding habitual activity. A sensation of pleasure must at least accompany the use of the organ before its existence can incite to its employment. And even so when a sensation of pleasure has given the impulse which is to render it active, it is only the fact of there being activity at all, and not the special characteristics of the activity, that can be due to organisation. The reason for the special mode of the activity is the very problem that we have to solve. No one will call the action of the spider instinctive in voiding the fluid from her spinning gland when it is too full, and therefore painful to her; nor that of the male fish when it does what amounts to much the same thing as this. The instinct and the marvel lie in the fact that the spider spins threads, and proceeds to weave her web with them, and that the male fish will only impregnate ova of his own species.
Another proof that the pleasure felt in the employment of an organ is wholly inadequate to account for this employment is to be found in the fact that the moral greatness of instinct, the point in respect of which it most commands our admiration, consists in the obedience paid to its behests, to the postponement of all personal well-being, and at the cost, it may be, of life itself. If the mere pleasure of relieving certain glands from overfulness were the reason why caterpillars generally spin webs, they would go on spinning until they had relieved these glands, but they would not repair their work as often as any one destroyed it, and do this again and again until they die of exhaustion. The same holds good with the other instincts that at first sight appear to be inspired only by a sensation of pleasure; for if we change the circumstances, so as to put self-sacrifice in the place of self-interest, it becomes at once apparent that they have a higher source than this. We think, for example, that birds pair for the sake of mere sexual gratification; why, then, do they leave off pairing as soon as they have laid the requisite number of eggs? That there is a reproductive instinct over and above the desire for sexual gratification appears from the fact that if a man takes an egg out of the nest, the birds will come together again and the hen will lay another egg; or, if they belong to some of the more wary species, they will desert their nest, and make preparation for an entirely new brood. A female wryneck, whose nest was daily robbed of the egg she laid in it, continued to lay a new one, which grew smaller and smaller, till, when she had laid her twenty-ninth egg, she was found dead upon her nest. If an instinct cannot stand the test of self-sacrifice—if it is the simple outcome of a desire for bodily gratification—then it is no true instinct, and is only so called erroneously.
Instinct is not a mechanism of brain or mind implanted in living beings by nature; for, if it were, then instinctive action without any, even unconscious, activity of mind, and with no conception concerning the purpose of the action, would be executed mechanically, the purpose having been once for all thought out by Nature or Providence, which has so organised the individual that it acts henceforth as a purely mechanical medium. We are now dealing with a psychical organisation as the cause instinct, as we were above dealing with a physical. A psychical organisation would be a conceivable explanation and we need look no farther if every instinct once belonging to an animal discharged its functions in an unvarying manner. But this is never found to be the case, for instincts vary when there arises a sufficient motive for varying them. This proves that special exterior circumstances enter into the matter, and that these circumstances are the very things that render the attainment of the purpose possible through means selected by the instinct. Here first do we find instinct acting as though it were actually design with action following at its heels, for until the arrival of the motive, the instinct remains late and discharges no function whatever. The motive enters by way of an idea received into the mind through the instrumentality of the senses, and there is a constant connection between instinct in action and all sensual images which give information that an opportunity has arisen for attaining the ends proposed to itself by the instinct.
The psychical mechanism of this constant connection must also be looked for. It may help us here to turn to the piano for an illustration. The struck keys are the motives, the notes that sound in consequence are the instincts in action. This illustration might perhaps be allowed to pass (if we also suppose that entirely different keys can give out the same sound) if instincts could only be compared with distinctly tuned notes, so that one and the same instinct acted always in the same manner on the rising of the motive which should set it in action. This, however, is not so; for it is the blind unconscious purpose of the instinct that is alone constant, the instinct itself—that is to say, the will to make use of certain means—varying as the means that can be most suitably employed vary under varying circumstances.