Instincts must have been either
1) Each specially created in complete form, or
2) Gradually evolved.
As the first alternative is nowadays obsolete, I proceed directly to the second. The two most prominent suggestions as to the way in which instincts may have been evolved are associated with the names of Lamarck and Darwin.
Lamarck's statement is that animals have wants, and contract, to satisfy them, habits which transform themselves gradually into so many propensities which they can neither resist nor change. These propensities, once acquired, propagate themselves by way of transmission to the young, so that they come to exist in new individuals, anteriorly to all exercise. Thus are the same emotions, the same habits, the same instincts, perpetuated without variation from one generation to another, so long as the outward conditions of existence remain the same.[562] Mr. Lewes calls this the theory of 'lapsed intelligence.' Mr. Spencer's words are clearer than Lamarck's, so that I will quote from him:[563]
"Setting out with the unquestionable assumption, that every new form of emotion making its appearance in the individual or the race is a modification of some pre-existing emotion, or a compounding of several pre-existing emotions, we should be greatly aided by knowing what always are the pre-existing emotions. When, for example, we find that very few, if any, of the lower animals show any love of accumulation, and that this feeling is absent in infancy; when we see that an infant in arms exhibits anger, fear, wonder, while yet it manifests no desire of permanent possession; and that a brute which has no acquisitive emotion can nevertheless feel attachment, jealousy, love of approbation,—we may suspect that the feeling which property satisfies is compounded out of simpler and deeper feelings. We may conclude that as when a dog hides a bone there must exist in him a prospective gratification of hunger, so there must similarly, at first, in all cases where anything is secured or taken possession of, exist an ideal excitement of the feeling which that thing will gratify. We may further conclude that when the intelligence is such that a variety of objects come to be utilized for different purposes; when, as among savages, divers wants are satisfied through the articles appropriated for weapons, shelter, clothing, ornament,—the act of appropriating comes to be one constantly involving agreeable associations, and one which is therefore pleasurable, irrespective of the end subserved. And when, as in civilized life, the property acquired is of a kind not conducing to one order of gratifications, but is capable of ministering to all gratifications, the pleasure of acquiring property grows more distinct from each of the various pleasures subserved—is more completely differentiated into a separate emotion.[564] It is well known that on newly-discovered islands not inhabited by man, birds are so devoid of fear as to allow themselves to be knocked over with sticks, but that in the course of generations they acquire such a dread of man as to fly on his approach, and that this dread is manifested by young as well as old. Now unless this change be ascribed to the killing off of the least fearful, and the preservation and multiplication of the more fearful, which, considering the small number killed by man, is an inadequate cause, it must be ascribed to accumulated experiences, and each experience must be held to have a share in producing it. We must conclude that in each bird that escapes with injuries inflicted by man, or is alarmed by the outcries of other members of the flock,... there is established an association of ideas between the human aspect and the pains, direct and indirect, suffered from human agency. And we must further conclude that the state of consciousness which impels the bird to take flight is at first nothing more than an ideal reproduction of those painful impressions which before followed man's approach; that such ideal reproduction becomes more vivid and more massive as the painful experiences, direct or sympathetic, increase; and that thus the emotion, in its incipient state, is nothing else than an aggregation of the revived pains before experienced. As, in the course of generations, the young birds of this race begin to display a fear of man before they have been injured by him, it is an unavoidable inference that the nervous system of the race has been organically modified by these experiences; we have no choice but to conclude that when a young bird is thus led to fly, it is because the impression produced on its senses by the approaching man entails, through an incipiently reflex action, a partial excitement of all those nerves which, in its ancestors, had been excited under the like conditions; that this partial excitement has its accompanying painful consciousness; and that the vague painful consciousness thus arising constitutes emotion proper—emotion undecomposable into specific experiences, and therefore seemingly homogeneous. If such be the explanation of the fact in this case, then it is in all cases. If the emotion is so generated here, then it is so generated throughout. If so, we must perforce conclude that the emotional modifications displayed by different nations, and those higher emotions by which civilized are distinguished from savage, are to be accounted for on the same principle. And, concluding this, we are led strongly to suspect that the emotions in general have severally thus originated."[565]
Obviously the word 'emotion' here means instinct as well,—the actions we call instinctive are expressions or manifestations of the emotions whose genesis Mr. Spencer describes. Now if habit could thus bear fruit outside the individual life, and if the modifications so painfully acquired by the parents' nervous systems could be found ready-made at birth in those of the young, it would be hard to overestimate the importance, both practical and theoretical, of such an extension of its sway. In principle, instincts would then be assimilated to 'secondarily-automatic' habits, and the origin of many of them out of tentative experiments made during ancestral lives, perfected by repetition, addition, and association through successive generations, would be a comparatively simple thing to understand.
Contemporary students of instinct have accordingly been alert to discover all the facts which would seem to establish the possibility of such an explanation. The list is not very long, considering what a burden of conclusions it has to bear. Let acquisitiveness and fear of man, as just argued for by Spencer, lead it off. Other cases of the latter sort are the increased shyness of the woodcock noticed to have occurred within sixty years' observation by Mr. T. A. Knight, and the greater shyness everywhere shown by large than by small birds, to which Darwin has called attention. Then we may add—
The propensities of 'pointing,' 'retrieving,' etc., in sporting dogs, which seem partly, at any rate, to be due to training, but which in well-bred stock are all but innate. It is in these breeds considered bad for a litter of young if its sire or dam have not been trained in the field.
Docility of domestic breeds of horses and cattle.
Tameness of young of tame rabbit—young wild rabbits being invincibly timid.
Young foxes are most wary in those places where they are most severely hunted.
Wild ducks, hatched out by tame ones, fly off. But if kept close for some generations, the young are said to become tame.[566]
Young savages at a certain age will revert to the woods.
English greyhounds taken to the high plateau of Mexico could not at first run well, on account of rarefied air. Their whelps entirely got over the difficulty.
Mr. Lewes somewhere[567] tells of a terrier pup whose parents had been taught to 'beg,' and who constantly threw himself spontaneously into the begging attitude. Darwin tells of a French orphan-child, brought up out of France, yet shrugging like his ancestors.[568]
Musical ability often increases from generation to generation in the families of musicians.
The hereditarily epileptic guinea-pigs of Brown-Séquard, whose parents had become epileptic through surgical operations on the spinal cord or sciatic nerve. The adults often lose some of their hind toes, and the young, in addition to being epileptic, are frequently born with the corresponding toes lacking. The offspring of guinea-pigs whose cervical sympathetic nerve has been cut on one side will have the ear larger, the eyeball smaller, etc., just like their parents after the operation. Puncture of the 'restiform body' of the medulla will, in the same animal, congest and enlarge one eye, and cause gangrene of one ear. In the young of such parents the same symptoms occur.
Physical refinement, delicate hands and feet, etc., appear in families well-bred and rich for several generations.
The 'nervous' temperament also develops in the descendants of sedentary brain-working people.
Inebriates produce offspring in various ways degenerate.
Nearsightedness is produced by indoor occupation for generations. It has been found in Europe much more frequent among schoolchildren in towns than among children of the same age in the country.
These latter cases are of the inheritance of structural rather than of functional peculiarities. But as structure gives rise to function it may be said that the principle is the same. Amongst other inheritances of adaptive[569] structural change may be mentioned:
The 'Yankee' type.
Scrofula, rickets, and other diseases of bad conditions of life.
The udders and permanent milk of the domestic breeds of cow.
The 'fancy' rabbit's ears, drooping through lack of need to erect them. Dog's, ass's, etc., in some breeds ditto.
The obsolete eyes of mole and various cave-dwelling animals.
The diminished size of the wing-bones of domesticated ducks, due to ancestral disuse of flight.[570]
These are about all the facts which, by one author or another, have been invoked as evidence in favor of the 'lapsed intelligence' theory of the origin of instincts.
Mr. Darwin's theory is that of the natural selection of accidentally produced tendencies to action.
"It would," says he, "be the most serious error to suppose that the greater number of instincts have been acquired by habit in one generation, and then transmitted by inheritance in succeeding generations. It can clearly be shown that the most wonderful instincts with which we are acquainted, namely, those of the hive-bee and of many ants, could not possibly have been thus acquired.[571] It will be universally admitted that instincts are as important as corporeal structure for the welfare of each species, under its present conditions of life. Under changed conditions of life, it is at least possible that slight modifications of instinct might be profitable to a species; and if it can be shown that instincts do vary ever so little, then I can see no difficulty in natural selection preserving and continually accumulating variations of instinct to any extent that may be profitable. It is thus, as I believe, that all the most complex and wonderful instincts have arisen.... I believe that the effects of habit are of quite subordinate importance to the effects of the natural selection of what may be called accidental variations of instincts;—that is, of variations produced by the same unknown causes which produce slight deviations of bodily structure."[572]
The evidence for Mr. Darwin's view is too complex to be given in this place. To my own mind it is quite convincing. If, with the Darwinian theory in mind, one re-reads the list of examples given in favor of the Lamarckian theory, one finds that many of the cases are irrelevant, and that some make for one side as well as for the other. This is so obvious in many of the cases that it is needless to point it out in detail. The shrugging child and the begging pup, e.g., prove somewhat too much. They are examples so unique as to suggest spontaneous variation rather than inherited habit. In other cases the observations much need corroboration, e.g., the effects of not training for a generation in sporting dogs and race-horses, the difference between young wild rabbits born in captivity and young tame ones, the cumulative effect of many generations of captivity on wild ducks, etc.
Similarly, the increased wariness of the large birds, of those on islands frequented by men, of the woodcock, of the foxes, may be due to the fact that the bolder families have been killed off, and left none but the naturally timid behind, or simply to the individual experience of older birds being imparted by example to the young so that a new educational tradition has occurred.—The cases of physical refinement, nervous temperament, Yankee type, etc., also need much more discriminating treatment than they have yet received from the Lamarckians. There is no real evidence that physical refinement and nervosity tend to accumulate from generation to generation in aristocratic or intellectual families; nor is there any that the change in that direction which Europeans transplanted to America undergo is not all completed in the first generation of children bred on our soil. To my mind, the facts all point that way. Similarly the better breathing of the greyhounds born in Mexico was surely due to a post-natal adaptation of the pups' thorax to the rarer air.
Distinct neurotic degeneration may undoubtedly accumulate from parent to child, and as the parent usually in this case grows worse by his own irregular habits of life, the temptation lies near to ascribe the child's deterioration to this cause. This, again, is a hasty conclusion. For neurotic degeneration is unquestionably a disease whose original causes are unknown; and like other 'accidental variations' it is hereditary. But it ultimately ends in sterility; and it seems to me quite unfair to draw any conclusions from its natural history in favor of the transmission of acquired peculiarities. Nor does the degeneration of the children of alcoholics prove anything in favor of their having inherited the shattered nervous system which the alcohol has induced in their parents: because the poison usually has a chance to directly affect their own bodies before birth, by acting on the germinal matter from which they are formed whilst it is still nourished by the alcoholized blood of the parent. In many cases, moreover, the parental alcoholics are themselves degenerates neurotically, and the drink-habit is only a symptom of their disease, which in some form or other they also propagate to their children.
There remain the inherited mutilations of the guinea-pig. But these are such startling exceptions to the ordinary rule with animals that they should hardly be used as examples of a typical process. The docility of domestic cattle is certainly in part due to man's selection, etc., etc. In a word, the proofs form rather a beggarly array.
Add to this that the writers who have tried to carry out the theory of transmitted habit with any detail are always obliged somewhere to admit inexplicable variation. Thus Spencer allows that
"Sociality can begin only where, through some slight variation, there is less tendency than usual for the individuals to disperse.... That slight variations of mental nature, sufficient to initiate this process, may be fairly assumed, all our domestic animals show us: differences in their characters and likings are conspicuous. Sociality having thus commenced, and survival of the fittest tending ever to maintain and increase it, it will be further strengthened by the inherited effects of habit."[573] Again, in writing of the pleasure of pity, Mr. Spencer says: "This feeling is not one that has arisen through the inherited effects of experiences, but belongs to a quite different group, traceable to the survival of the fittest simply—to the natural selection of incidental variations. In this group are included all the bodily appetites, together with those simpler instincts, sexual and parental, by which every race is maintained; and which must exist before the higher processes of mental evolution can commence."[574]
The inheritance of tricks of manner and trifling peculiarities, such as handwriting, certain odd gestures when pleased, peculiar movements during sleep, etc., have also been quoted in favor of the theory of transmission of acquired habits. Strangely enough; for of all things in the world these tricks seem most like idiosyncratic variations. They are usually defects or oddities which the education of the individual, the pressure of what is really acquired by him, would counteract, but which are too native to be repressed, and breaks through all artificial barriers, in his children as well as in himself.
I leave my text practically just as it was written in 1885. I proceeded at that time to draw a tentative conclusion to the effect that the origin of most of our instincts must certainly be deemed fruits of the back-door method of genesis, and not of ancestral experience in the proper meaning of the term. Whether acquired ancestral habits played any part at all in their production was still an open question in which it would be as rash to affirm as to deny. Already before that time, however, Professor Weismann of Freiburg had begun a very serious attack upon the Lamarckian theory,[575] and his polemic has at last excited such a widespread interest among naturalists that the whilom almost unhesitatingly accepted theory seems almost on the point of being abandoned.
I will therefore add some of Weismann's criticisms of the supposed evidence to my own. In the first place, he has a captivating theory of descent of his own,[576] which makes him think it a priori impossible that any peculiarity acquired during lifetime by the parent should be transmitted to the germ. Into the nature of that theory this is not the place to go. Suffice to say that it has made him a keener critic of Lamarck's and Spencer's theory than he otherwise might have been. The only way in which the germinal products can be influenced whilst in the body of the parent is, according to Weismann, by good or bad nutrition. Through this they may degenerate in various ways or lose vitality altogether. They may also be infected through the blood by small-pox, syphilis, or other virulent diseases, and otherwise be poisoned. But peculiarities of neural structure and habit in the parents which the parents themselves were not born with, they can never acquire unless perhaps accidentally through some coincidental variation of their own. Accidental variations develop of course into idiosyncrasies which tend to pass to later generations in virtue of the well-known law which no one doubts.
Referring to the often-heard assertion that the increase of talent found in certain families from one generation to another is due to the transmitted effects of exercise of the faculty concerned (the Bachs, the Bernoullis, Mozart, etc.), he sensibly remarks, that the talent being kept in exercise, it ought to have gone on growing for an indefinite number of generations. As a matter of fact, it quickly reaches a maximum, and then we hear no more of it, which is what happens always when an idiosyncrasy is exposed to the effects of miscellaneous intermarriage.
The hereditary epilepsy and other degenerations of the operated guinea-pigs are explained by Professor Weismann as results of infection of the young by the parent's blood. The latter he supposes to undergo a pathologic change in consequence of the original traumatic injury. The obsolescence of disused organs he explains very satisfactorily, without invoking any transmission of the direct effects of disuse, by his theory of panmixy, for which I must refer to his own writings. Finally, he criticises searchingly the stories we occasionally hear of inherited mutilations in animals (dogs' ears and tails, etc.), and cites a prolonged series of experiments of his own on mice, which he bred for many generations, cutting off both parental tails each time, without interfering in the least with the length of tail with which the young continued to be born.
The strongest argument, after all, in favor of the Lamarckian theory remains the a priori one urged by Spencer in his little work (much the solidest thing, by the way, which he has ever written) 'The Factors of Organic Evolution.' Since, says Mr. Spencer, the accidental variations of all parts of the body are independent of each other, if the entire organization of animals were due to such accidental variations alone, the amount of mutual adaptation and harmony that we now find there could hardly possibly have come about in any finite time. We must rather suppose that the divers varying parts brought the other parts into harmony with themselves by exercising them ad hoc, and that the effects of the exercise remained and were passed on to the young. This forms, of course, a great presumption against the all-sufficiency of the view of selection of accidental variations exclusively. But it must be admitted that in favor of the contrary view, that adaptive changes are inherited, we have as yet perhaps not one single unequivocal item of positive proof.
I must therefore end this chapter on the genesis of our mental structure by reaffirming my conviction that the so-called Experience-philosophy has failed to prove its point. No more if we take ancestral experiences into account than if we limit ourselves to those of the individual after birth, can we believe that the couplings of terms within the mind are simple copies of corresponding couplings impressed upon it by the environment. This indeed is true of a small part of our cognitions. But so far as logical and mathematical, ethical, æsthetical, and metaphysical propositions go, such an assertion is not only untrue but altogether unintelligible; for these propositions say nothing about the time- and space-order of things, and it is hard to understand how such shallow and vague accounts of them as Mill's and Spencer's could ever have been given by thinking men.
The causes of our mental structure are doubtless natural, and connected, like all our other peculiarities, with those of our nervous structure. Our interests, our tendencies of attention, our motor impulses, the æsthetic, moral, and theoretic combinations we delight in, the extent of our power of apprehending schemes of relation, just like the elementary relations themselves, time, space, difference and similarity, and the elementary kinds of feeling, have all grown up in ways of which at present we can give no account. Even in the clearest parts of Psychology our insight is insignificant enough. And the more sincerely one seeks to trace the actual course of psychogenesis, the steps by which as a race we may have come by the peculiar mental attributes which we possess, the more clearly one perceives "the slowly gathering twilight close in utter night."