It has often been maintained that the existence of animal instincts is in itself enough to prove that the Lamarckian principle is operative. In one of the earlier lectures I showed that at least the greater number of instincts must have originated in purely reflex actions, and therefore, like these actions themselves, can only be explained through natural selection. A reflex action, such as coughing, sneezing, shutting of the eyelids, and so on, differs from an instinctive action in the lesser complexity and shorter duration of the series of movements liberated by a sense-impression, and also in that it does not require to enter into consciousness at all; but no very precise boundary can be drawn between the two, and, in any case, both depend, as we have already seen, on a quite analogous anatomical basis. It is only a difference in degree whether, at the sight of a rapidly approaching object, the muscles of the eyelids contract, and by shutting the lids, protect the eye, or whether the fly, which we intend to seize with our hand, is impelled by the sight of the rapidly approaching shadow of the hand to fly quickly up. The action of the fly may be regarded as reflex, or equally well as instinctive. But there is also only a difference in degree, not in kind, between this simple action and the complex and protracted behaviour of a mason-bee, the sight of whose colony impels her to fly out and fetch clay, with it gradually to build a neat cell, to fill this with honey, to lay an egg in it, and finally to furnish the cell with a roof of clay. Since all reflex mechanisms, and all the natural instincts of animals, contribute to the maintenance of the species, and are therefore useful, their origins must be referable to natural selection, and we have only to ask whether they must be referred to it always, and to it alone.
It cannot be doubted that, in Man, and in the higher animals voluntary actions which are often repeated gradually acquire the character of instinctive actions. The individual movements pertaining to the particular action are no longer each guided by the will, but a single exercise of will is enough to liberate the whole complex action, such as writing, speaking, walking, or the playing of a whole piece of music; frequently the will-impulse may be absent altogether, and the action be set going simply by an adequate external stimulus, as in the case of sleep-walking, which is observed in fatigued children and soldiers, and in somnambulists. The external stimulus is transmitted to the proper group of muscles as unfailingly as in the case of true instincts, and this happens not only in regard to actions which, like walking, are essential to the life of the species, but also in regard to those which have arisen from chance habits or exercises. Often a short practice is sufficient to make an action in this sense instinctive, and the complexity of the instinct-mechanism gained by such practice is often astounding. Under some circumstances a person may play a piece on the piano from the score, and yet be thinking intently of other things, and be quite unconscious of what is played. In the same way it may happen that a person dominated by violent emotion, when trying to free himself from it by reading, may read a whole page, line by line, without understanding in the least what has been read. In the last case it is not directly demonstrable that the reader has made all the complex delicate eye-movements which would be liberated by the sight of the words, but in the case of playing, the listeners can perceive that the piece is correctly played, and thus that the stimulus exercised by each note on the retina of the eye is translated into the complex muscular movement of arm and finger, corresponding both to the pitch and the duration of the note, and to the simultaneousness of several notes.
In all these cases it is probably not always quite new paths which are established in the brain, but use is made of particular tracks in the innumerable nerve-paths already existing in the nerve-cells (neurons) which are 'more thoroughly trodden' by practice, so that the distribution of the nerve-current takes place more easily along them than along others[13]. This much-used metaphor does not indicate the actual structural changes which have taken place, but it serves at least to indicate that we have to do with material changes in the ultimate living elements of the nerve-substance (nerve-biophors) whether these changes be in position or in quality. Now, if such brain-structures and mechanisms acquired through exercise in the individual life could be transmitted, new instincts would certainly arise in this way, and many naturalists hold this view still.
[13] This, however, is by no means intended to cast doubt on the possibility that quite new paths may arise during the individual life, as is made probable by the recent investigations of Apáthy, Bethe, and others.
If the inheritance of acquired characters had already been proved in other ways, we could not refuse to admit that it might play a part in the higher animals in the modification and new formation of instincts. We should then have to admit that habits can be inherited, and that instincts actually are or may be, as they have often been said to be, inherited habits. But to make the converse conclusion, and to infer from the result of the brain-exercise in the individual life and its similarity to inborn instincts that the latter also depend on inherited exercise, and that there must therefore be inheritance of acquired characters, is hardly admissible.
It might be all very well if there were no other explanation! But as instincts depend on material brain-mechanisms which are variable, like every other part of the body, and as, furthermore, they are essential to the existence of the species, and, down to the minutest detail, are adapted to the circumstances of life, there is no obstacle in the way of referring their origin and transformation to processes of selection.
It has been asserted that the results of training, for instance in dogs, can be inherited, since the untaught young pointer points at the game, and the young sheep-dog runs round and barks at the flock of sheep without biting them. It is, however, often forgotten that, not only have these breeds arisen under the influence of artificial selection by Man, but that they are even now strictly selected. My colleague and friend, Dr. Otto vom Rath, who unhappily died all too soon for Science, and who was not only a capable investigator, but an experienced sportsman, told me that huntsmen distinguish very carefully between the better and the inferior young in a litter, and that by no means every whelp of a pair of pointers can be used for hunting game-birds. Lloyd Morgan points out the same thing, and he is undoubtedly a competent judge in the domain of instinct; he confirms the statement that the pointer 'often points at the quarry, it may be a lark's nest, without instruction,' but he says at the same time, that the power is inborn in very varying degrees, and that, in his opinion, selection undoubtedly plays a part.
It must not, therefore, be believed that the habit of the pointer depends on training; it is only strengthened in each individual by training, but it depends on an innate predisposition to creep up to the game, and is thus a form of the hunting instinct. Man has taken advantage of this, and has increased it, but has certainly not ingrafted it into the breed by whipping. And something similar will be found to be true in all cases of so-called inheritance of the effects of training. It must not be forgotten what astounding results can be achieved in the individual by training. The elephant is the best example of this, for it only exceptionally breeds in captivity, and all the thousands of 'domesticated' elephants in India are tamed wild elephants. Yet they are as gentle and docile as the horse, which has been domesticated for thousands of years; they perform all kinds of tasks with the greatest patience and carefulness, in many cases without being under constant superintendence. They are indeed animals of great intelligence; they understand what is required of them, and they accommodate themselves readily to new conditions of life.
The attachment of the dog to its master and to Man generally has often been cited as a proof of the origin of a new instinct by the inheritance of acquired habitude; but the dog is a sociable animal even in a wild state, and by living in co-operative association with Man it has transferred its sociable affections to him. We find exactly the same thing in the elephant which has been caught wild and tamed. It is particularly emphasized by those who have accompanied animal transports in Africa that the young elephants are wild and malicious towards the blacks who teased and maltreated them, but complaisant and harmless towards the whites who treated them kindly. The attachment of elephants to their keepers and to every one who shows them kindness is familiar enough; it does not depend on a newly acquired impulse, but on the sociable impulse inherent in the species, which, in the wild state, causes them to live in fairly large companies, and on their inoffensive, timid, and, we may almost say, affectionate disposition.
Of course it is easy enough to give an imaginative theoretical interpretation of the origin of a new instinct from a newly acquired habit. We have often heard that sailors have found the birds in distant uninhabited islands quite free from fear; they let themselves be struck down with cudgels without attempting to escape. The extermination of the Dodo three centuries ago is a well-known example of this. Chun, in his magnificent work on the German Deep Sea Expedition of 1898, has recently communicated numerous interesting examples of the indifference of birds towards Man when they have not learned what his presence means: thus the sea-birds of Kerguelen, penguins, cormorants, gulls, 'kelp-pigeons' (Chionis), and others, behaved towards Man very much like the tame geese of our poultry yards. Even enormous mammals like the 'sea-elephant,' a seal with a proboscis-like prolongation of the nose, neither attempted to escape nor showed any hostility to man, but quietly let itself be caught. Similar tales were told by Steller in 1799, after he had been obliged to pass a winter with his sailors on an island in the Behring Straits. The numerous gigantic sea-cows (Rhytina stelleri) which lived there were so confiding that they allowed the boat to come quite up to them, and the sailors were able to kill many of them from time to time, using their flesh for food. But towards the end of the winter the animals began to be shy, and, in the following winter, when other sailors to the polar regions endeavoured to hunt them too, it was very difficult to secure them; they had recognized man as an enemy, and fled from him when they saw him from afar. Thus the same individuals which had earlier carelessly allowed man to come up to them now avoided him as an enemy. This was not instinct, it was a behaviour controlled by the will and founded on experience. But it would soon become 'instinctive' if the meeting with the enemy were often repeated, just like the winding-up of a watch, which is often done at a wrong time, for instance, on changing clothes during the day, and thus without reflection. It is quite easy to conceive that if the material brain-adaptation which causes flight without reflection at the sight of man were transmissible, the flight-instinct might become a congenital instinct in the species in question. But this assumption is unfounded; for, as is shown by the case of the sea-cow, we do not require it where the animal is of sufficient intelligence to perform by its own discernment the action necessary to its existence. The action may thus become 'instinctive' through exercise and imitation in the individual life, without however attaining to transmissibility.