THE MODERN THEORY OF INSTINCT

The Hunting Wasps by Jean-Henri Fabre, is part of the HackerNoon Books Series. You can jump to any chapter in this book here. THE MODERN THEORY OF INSTINCT

Chapter XX. THE MODERN THEORY OF INSTINCT

The larvæ of the various Hunting Wasps require their prey to be incapable of movement, so that there may be no resistance on the victim’s part, which would be a source of danger to the fragile egg and, later, to the grub. Moreover, for all its lethargy, it must still be alive; for the grub would refuse to feed on a corpse. The fare provided must be fresh meat and not preserved stuff. I have already laid stress on these two antagonistic conditions, immobility and life, and enlarged on them so fully that I need hardly dwell upon them for a second time. I have shown how the Wasp realizes them by the medium of a paralysis which destroys movement and leaves the organic principle of life intact. With a skill which our most famous vivisectors would envy, the insect drives its poisoned sting into the nerve-centres, the seat of muscular incitation. The operator confines herself to one stroke of the lancet, or else gives two, three or more, according to the structure of the particular nervous system and to the number and grouping of the ganglia. The course of the sting is determined by the exact anatomy of the victim.

The particular prey of the Hairy Ammophila is a caterpillar, each of whose nerve-centres, which are distant one from the other and to a certain extent independent in their action, occupies a different segment of the insect. This caterpillar, who is a very lively customer, cannot be stored in the cell, with the Wasp’s egg upon his flank, until he has lost all his power of motion. One movement of his body would crush that egg against the wall of the cell.

Now the paralysis of one segment would not mean that the next was also rendered incapable of movement, because of the comparative independence of the seats of innervation. It is necessary, therefore, that all the segments, or at least the most important, be operated on, one after the other, from the first to the last. The course which the Ammophila adopts is that which the most experienced of physiologists would recommend: her sting is transferred from one segment to the next, nine separate times over.

She does better than that. The victim’s head is still unscathed, the mandibles are at work: they might easily, as the insect is borne along, grip some bit of straw in the ground and successfully resist this forcible removal; the brain, the primary nervous centre, might provoke a stubborn contest, which would be very awkward with so heavy a burden. It is well that these hitches should be avoided. The caterpillar, therefore, must be reduced to a state of torpor which will deprive him of the least inclination for self-defence. The Ammophila succeeds in effecting this by munching his head. She takes good care not to use her needle: she is no clumsy bungler and knows quite well that to inflict a mortal wound on the cervical ganglia would mean killing the caterpillar then and there, the very thing to be avoided. She merely squeezes the brain between her mandibles, calculating every pinch; and, each time, she stops to ascertain the effect produced, for there is a nice point to be achieved, a certain degree of torpor that must not be exceeded, lest death should supervene. In this way the requisite lethargy is obtained, a somnolence in which all volition is lost. And now the caterpillar, incapable of resistance, incapable of wishing to resist, is seized by the nape of the neck and dragged to the nest. Comment would mar the eloquence of such facts as these.

The Hairy Ammophila has twice allowed me to attend her surgical operations. I have described in an earlier chapter of this volume my first observation, which dates many years back. On that occasion I witnessed the performance quite unexpectedly; to-day, I have made all my preparations and have plenty of time at my disposal, so that I am able to make a much more thorough observation. In each case there was a multiplicity of needle-pricks, which were distributed methodically, from front to back, along the ventral surface. Is the number of stings indeed identical in both cases? This time, it is exactly nine. In the case of the victim which I saw paralysed on the Plateau des Angles, it seemed to me that the weapon inflicted more wounds, though I am not able to state the precise number. It is quite possible that this number varies slightly and that the last segments of the caterpillar, being much less important than the others, are attacked or left alone according to the size and strength of the quarry to be incapacitated.

On the second occasion, moreover, I had my first view of the squeezing process to which the caterpillar’s brain is subjected, a process that produces the torpor which makes the transport and storage of the victim possible. So remarkable a fact would not have escaped me in the first instance; it did not, therefore, take place. It follows that this cerebral compression is a resource which the Wasp has at her disposal, for use when circumstances demand it, as for instance when the victim seems likely to offer resistance on the road.

The malaxation of the cervical ganglia is optional: it has no bearing on the future of the larva; the Wasp practises it, when needful, to facilitate transport. I have seen the Languedocian Sphex, who gave me so much trouble in the old days, at work fairly often, but only once has she performed this operation on the neck of her Ephippiger in my presence. The invariable and absolutely necessary part of the Hairy Ammophila’s procedure seems therefore to be the multiplicity of stings and their distribution one by one over all or nearly all the nerve-centres along the median line of the lower surface.

Let us place side by side with the murderous art of the Wasp the murderous art of man, practical man, whose business it is to slay rapidly. I will here recall one of my childhood’s memories. We were schoolboys of twelve years old, or thereabouts. We were being instructed in the woes of Melibœus, pouring out his sorrows on the bosom of Tityrus, who offers him his chestnuts, his sour milk and his bed of fresh bracken;1 we were made to recite a poem by Racine the Younger,2 La Religion. A curious poem, forsooth, for children who cared more for marbles than theology! I remember just two lines and a half:

… et, jusque dans la fange,

L’insecte nous appelle et, certain de son prix,

Ose nous demander raison de nos mépris.3

Why do these two lines and a half linger in my memory and none of all the rest? Because already Scarabæus and I were friends. Those two lines and a half bothered me: I thought it a very absurd idea to relegate you to the mire, ye insects so seemly clad, so elegantly groomed. I knew the bronze harness of the Carabus, the Russia-leather jerkin of the Stag-beetle; I knew that the least of you possesses an ebon sheen and gleams of precious metals; and therefore the mire wherein the poet flung you shocked me somewhat. If M. Racine Junior had nothing better to say about you, he might as well have held his tongue; but he did not know you, and in his day there were only just a few who were beginning to have a dim conception of your nature.

While going over some passage of the tiresome poem for the next day’s lesson, I would indulge my fancy for another kind of education. I visited the Linnet in her nest, on a juniper-bush standing as high as myself; I watched the Jay picking an acorn on the ground; I came upon the Crayfish, still quite soft after shedding his shell; I made inquiries as to the exact date when the Cockchafers were due; I went in quest of the first full-blown Cuckoo-flower. Plants and animals, that wondrous poem of which a faint echo was beginning to wake in my young brain, made a very pleasant change from the uninspiring alexandrine. The problem of life and that other one, with its dark terrors, the problem of death, at times passed through my mind. It was a fleeting obsession, soon forgotten by the mercurial spirits of youth. Nevertheless, the tremendous question would recur, brought to mind by this incident or that.

Passing one day by a slaughter-house, I saw an Ox driven in by the butcher. I have always had an insurmountable horror of blood; when I was a boy, the sight of an open wound affected me so much that I would fall into a swoon, which on more than one occasion nearly cost me my life. How did I screw up courage to set foot in those shambles? No doubt, the dread problem of death urged me on. At any rate, I entered, close on the heels of the Ox.

With a stout rope round its horns, wet-muzzled, meek-eyed, the animal moves along as though making for the crib in its stable. The man walks ahead, holding the rope. We enter the hall of death, amid the sickening stench thrown up by the entrails scattered over the ground and the pools of blood. The Ox becomes aware that this is not his stable; his eyes turn red with terror; he struggles; he tries to escape. But an iron ring is there, in the floor, firmly fixed to a stone flag. The man passes the rope through it and hauls. The Ox lowers his head; his muzzle touches the ground. While an assistant keeps him in this position with the rope, the butcher takes a knife with a pointed blade, not at all a formidable knife, hardly larger than the one which I myself carry in my breeches-pocket. For a moment he feels with his fingers at the back of the animal’s neck and then drives in the blade at the chosen spot. The great beast gives a shiver and drops, as though struck by lightning: procumbit humi bos, as we used to say in those days.

I fled from the place like one possessed. Afterwards I wondered how it was possible, with a knife almost identical with that which I used for prizing open my walnuts and taking the skin off my chestnuts, with that insignificant blade, to kill an Ox and kill him so suddenly. No gaping wound, no blood spilt, not a bellow from the animal. The man feels with his finger, gives a jab and the thing is done: the Bullock’s legs double up under him.

This instantaneous death, this lightning-stroke, remained an awesome mystery to me. It was only later, very much later, that I learnt the secret of the slaughter-house, at a time when, in the course of my promiscuous reading, I was picking up a smattering of anatomy. The man had cut through the spinal marrow where it leaves the skull; he had severed what our physiologists have called the vital cord. To-day I might say that he had operated in the manner of the Wasps, whose lancet plunges into the nerve-centres.

Let us watch this spectacle a second time, under more exciting conditions: I mean, in the saladeiros of South America, those immense establishments for killing and treating meat, where they slaughter as many as twelve hundred Oxen a day. I will quote the account of an eye-witness:4

‘The cattle arrive in large herds and the matance begins on the day after the arrival. A whole herd is confined in an enclosed space, or margueira. From time to time men on horseback drive fifty or sixty beasts into a narrower and stronger enclosure, with a sloping floor of brick, boards or concrete, which is always very slippery. A special operator, standing on an outer platform which runs along the wall of the smaller margueira, lassoes one of the crowd of animals by the head or, more often, by the horns. The middle portion of the long, stout lasso is coiled round a windlass; and a draught-horse, or sometimes a pair of oxen, drags the lassoed beast along and makes it slide, in spite of its struggles, right against the windlass, where it is brought up with a thud and remains without power of movement.

‘Another assistant, the desnucador, also standing on the platform, has then but to stick a knife, at the back of the head, between the occipital bone and the axis; and the paralysed animal topples on to a trolley in which it is carted off. It is at once thrown on an inclined plane where other special labourers bleed it and skin it. But, as the injury to the cervical marrow varies a good deal in position and extent, it often happens that the unfortunate beasts still retain the motions of the heart and of the respiratory organs; and, in such cases, they suffer a reaction under the knife; they utter faint sounds of pain and move their limbs, while already half-flayed and disembowelled. Nothing could be more painful than the sight of all those animals skinned alive, cut up and transformed by those men, covered with blood, who run about in all directions.’

The murderous methods of the saladeiro are an exact repetition of what I had seen in the slaughter-house. In both these lethal work-shops they pierce the vertebral marrow at the base of the skull. The Ammophila operates in a similar fashion, with this difference, that her surgery is much more complex, much more difficult, because of the peculiar organization of her victim. The honours are on her side again when we consider the delicacy of the result obtained. Her caterpillar is not a corpse, like the Ox whose spinal cord is cut; it is alive, but incapable of movement. The insect here is man’s superior in all respects.

Now how did the butcher of our parts and the desnucador of the pampas light upon the idea of plunging a knife into the seat of the marrow, in order to produce the sudden death of a colossus which would never suffer its throat to be cut without first offering a dangerous resistance? Outside those in the trade and men of science, nobody knows or suspects the lightning result of that particular wound; we are almost all in the same state of ignorance on this subject in which I myself was when my childish curiosity drew me into the killing-shed. The desnucador and the butcher have learnt their craft from the teachings of tradition and example: they have had masters; and these were brought up in the school of other masters, harking back by a chain of linked traditions to him who, served, no doubt, by some hazard of the chase, first realized the tremendous effects of a wound in the nape of the neck. Who shall tell us that a pointed flint-stone, driven by accident into the spinal marrow of the Reindeer or the Mammoth, did not rouse the attention of the desnucador’s forerunner? A casual incident furnished the original idea; observation confirmed it; reflection matured it; tradition preserved it; example disseminated it. After that, the same transmission-current. For generation might follow generation in vain: deprived of masters, the desnucador’s descendants would return to the primitive state of ignorance. Heredity does not hand down the art of killing by severing the spinal marrow: no man is born a cattle-slayer by the desnucador’s method.

Now here is the Ammophila, a slayer of caterpillars by a far more cunning method. Where are the professors of the art of stinging? There are not any. When the Wasp rends her cocoon and issues from underground, her predecessors have long ceased to live; she herself will perish without seeing her successors. Once the larder is stocked and the egg laid, all connection with the offspring ends; this year’s perfect insect dies while next year’s insect, still in the larval stage, slumbers below ground in its silken cot. Absolutely nothing, therefore, is transmitted by practical illustration. The Ammophila is born a finished desnucador even as we are born feeders at our mother’s breast. The nurseling uses its suction-pump, the Ammophila her dart, without ever being taught; and both are past masters of the difficult art from the first attempt. There we have instinct, the unconscious impulse that forms an essential part of the conditions of life and is handed down by heredity in the same way as the rhythmic action of the heart and lungs.

Let us try, if possible, to trace the Ammophila’s instinct to its source. We suffer to-day, more than we ever did, from a mania for explaining what might well be incapable of explanation. There are some—and their number seems to increase daily—who settle the stupendous question with magnificent audacity. Give them half-a-dozen cells, a bit of protoplasm and a diagram for demonstration; and they will account to you for everything. The organic world, the intellectual and moral world, everything derives from the original cell, evolving by means of its own energies. It’s as simple as A B C. Instinct, roused by a chance action that has proved favourable to the animal, is an acquired habit. And men argue on this basis, invoking natural selection, heredity, the struggle for life. I see plenty of big words, but I should prefer a few small facts. These little facts I have been collecting and catechizing for nearly forty years; and their replies are not exactly in favour of current theories.

You tell me that instinct is an acquired habit, that a casual circumstance, propitious to the animal’s offspring, was the first to prompt it. Let us look into the thing more closely. If I understand aright, we must suppose some Ammophila, in a very remote past, to have accidentally injured her caterpillar’s nervous centres; to have found herself the gainer by this operation, both as regards herself, in being released from a struggle not unattended with danger, and as regards her larva, thus supplied with fresh, living and yet harmless victuals; and consequently to have endowed her offspring, by heredity, with a natural tendency to repeat the advantageous device. The maternal legacy did not benefit all the descendants equally: some were poor hands at the newborn art of the stiletto; others were adepts. Then came the struggle for existence, the hateful væ victis! The weak went under, the strong flourished; and, as age succeeded age, selection by vital competition changed the fleeting impression of the start into a deep-rooted, ineffaceable impression, exemplified in the masterly instinct which we admire in the Wasp to-day.

Well, I avow, in all sincerity, this is asking a little too much of chance. When the Ammophila first found herself in the presence of her caterpillar, there was nothing, you would have it, to guide the sting. The choice was made at random. The pricks were directed at the upper surface of the captured prey, at the lower surface, at the sides, the front and the back indiscriminately, according to the fortunes of a close struggle. The Hive-bee and the Social Wasp sting those points which they are able to reach, without showing a preference for one part over the other. That is how the Ammophila must have acted, when still ignorant of her art.

Now how many points are there in a Grey Worm, above and below? Mathematical accuracy would answer, an infinity; a few hundreds will serve our purpose. Of this number, nine or perhaps more have to be selected; the needle must be inserted there and not elsewhere: a little higher, a little lower, a little to one side, it would not produce the desired effect. If the favourable event is a purely accidental result, how many combinations would be needed to bring it about, how much time to exhaust all the possible cases? When the difficulty becomes too pressing, you take refuge behind the mist of the ages; you retreat into the shadows of the past as far as fancy can carry you; you call upon time, that factor of which we have so little at our disposal and which, for this very reason, is so well suited to hide our illusions. Here you can let yourselves go and lavish the centuries. Suppose we shake up hundreds of figures, all of different values, in an urn and draw nine at random. When shall we, in this way, obtain a sequence fixed beforehand, a sequence that stands alone? The chance is so slight, answers mathematics, that we may as well put it down as nil and say that the desired arrangement will never come about. For the Ammophila of the prehistoric age, the attempt was renewed only at long intervals, from one year to the next. Then how did this sequence of nine stings at nine selected points emerge from the urn of chance? When I am driven to appeal to infinity in time, I am very much afraid of running up against absurdity.

‘But,’ say you, ‘the insect did not attain its present surgical dexterity at the outset: it went through experiments, apprenticeships, varying degrees of skill. There was a weeding-out by natural selection, eliminating the less expert, retaining the more gifted; and instinct, as we know it, developed gradually, thanks to the accumulation of individual capacities, added to those handed down by heredity.’

The argument is erroneous: instinct developed by degrees is flagrantly impossible in this case. The art of preparing the larva’s provisions allows of none but masters and suffers no apprentices; the Wasp must excel in it from the outset or leave the thing alone. Two conditions, in fact, are absolutely essential: that the insect should be able to drag home and store a quarry which greatly surpasses it in size and strength; and that the newly-hatched grub should be able to gnaw peacefully, in its narrow cell, a live and comparatively enormous prey. The suppression of all movements in the victim is the only means of realizing these conditions; and this suppression, to be complete, requires sundry dagger-thrusts, one in each motor centre. If the paralysis and the torpor be not sufficient, the Grey Worm will defy the efforts of the huntress, will struggle desperately on the road and will not reach the journey’s end; if the immobility be not complete, the egg, fixed at a given spot on the worm, will perish under the contortions of the giant. There is no via media, no half-success. Either the caterpillar is treated according to rule and the Wasp’s family is perpetuated; or else the victim is only partially paralysed and the Wasp’s offspring dies in the egg.

Yielding to the inexorable logic of things, we will therefore admit that the first Hairy Ammophila, after capturing a Grey Worm to feed her larva, operated on the patient by the exact method in use to-day. She seized the creature by the skin of the neck, stabbed it underneath, opposite each of the nerve-centres and, if the monster threatened further resistance, munched its brain. It must have happened like this; for, once more, an unskilled murderess, doing her work in a perfunctory and haphazard fashion, would leave no successor, since the rearing of the egg would become impossible. Save for the perfection of her surgical powers, the slayer of fat caterpillars would die out in the first generation.

Again I hear you say:

‘The Hairy Ammophila, before hunting the Grey Worm, may have picked out feebler caterpillars and heaped up several in one cell, until they represented the same bulk of provender as the big prey of to-day. With puny game, a few thrusts of the needle, perhaps one, would be enough. Gradually, large-sized prey came to be preferred, as reducing the number of hunting expeditions. Then, as successive generations went after bigger game, the dagger-strokes were multiplied, in proportion to the victim’s power of resistance; and, by degrees, the elementary instinct of the outset became the highly-developed instinct of our time.’

To these arguments we may begin by replying that the larva’s change of diet and the substitution of one morsel for a number are diametrically opposed to what happens before our eyes. The Hunting Wasp, as we know her, is extremely loyal to old customs; she has sumptuary laws which she never transgresses. She who fed on Weevils in her youth puts Weevils and naught else in her larva’s cell; she who was supplied with Buprestis-beetles persists in the fare which she has adopted and serves her larva with Buprestis-beetles. One Sphex must have Crickets; a second, Grasshoppers; a third, Locusts. Nothing is accepted but these particular dishes. The Bembex who hunts Gad-flies revels in them and refuses to do without them, whereas Stizus ruficornis, who fills the larder with Praying Mantes, scorns any other game. And so with the rest. They have each their own taste.

It is true that many allow themselves a more varied bill of fare, but only within the limits of one entomological group: thus the Weevil and Buprestis hunters prey upon any species proportioned to their strength. Were the Hairy Ammophila to make a change in her diet, that would be her case too. Whether small and sundry to each cell or large and single, the prey would always consist of caterpillars. So far, so good. But there remains the question of the many replaced by the unit; and I do not yet know one instance of such an alteration in the Wasp’s habits. She who stocks the burrow with a single joint never thinks of heaping up several of smaller size; she who goes on repeated expeditions to stack a quantity of game in the same cell does not know how to limit herself to one head by choosing larger meat. The result of my observations never varies in this regard. The prehistoric Ammophila, who abandoned her multiplicity of small game for one colossal head, has nothing to warrant her existence.

If the point were conceded, would the question be advanced? Not in the least. Let us accept as the initial prey a feeble caterpillar, paralysed with a single sting. Even then that sting must not be given at random, else the act would be more harmful than profitable. Irritated, but not subdued by the wound, the animal would but become more dangerous. The dart must strike a nerve-centre, probably in the middle region of the string of ganglia. This, at any rate, is how the present-day Ammophilæ seem to go to work when they are addicted to the rape of frail and slender grubs. What chance would the operator have of striking that one particular point, if her lancet were wielded without method? The probability is ludicrously remote: it is as one to the countless number of points whereof the caterpillar’s body is made up. And yet, according to the theorists, it is on this probability that the Wasp’s future depends. What an edifice to balance on the point of a needle!

Let us go on admitting and continue. The desired point is struck; the prey is duly paralysed; the egg laid on its flank will develop in safety. Is that enough? It is at most but a half of what is absolutely necessary. Another egg is indispensable to complete the future couple and ensure offspring. Therefore, within a few days’, within a few hours’ interval, a second sting must be given, as successful as the first. In other words, the impossible has to be repeated, the impossible raised to the second degree.

Let us not be discouraged yet; let us sound the uttermost depths of the problem. Here is a Wasp, some precursor, no matter which, of our Ammophila, who, favoured by chance, has twice and perhaps oftener succeeded in reducing the prey to that state of inertia which the rearing of the egg imperatively demands. She does not know, does not suspect that she inserted her sting opposite a nerve-centre rather than elsewhere. As there was nothing to prompt her choice, she acted at random. Nevertheless, if we are to take the theory of instinct seriously, we shall have to admit that this fortuitous action, though a matter of indifference to the insect, left a lasting trace and made so great an impression that, henceforth, the cunning stratagem which produces paralysis by attacking the nervous centres is transmissible by heredity. The Ammophila’s successors, by some prodigious privilege, will inherit what the mother did not possess. They will know by instinct the point or points towards which the sting must be directed; for, if they were still in the prentice stage, if they and their successors had to risk the chance that accident would tend gradually to strengthen the nascent impulse, they would be going back to the likelihood so near allied to nil; they would go back to it year by year, for centuries to come; and yet the one and only favourable chance would have to be always recurring. I find it very difficult to believe in a habit acquired by this prolonged repetition of incidents whereof not one can take place without excluding so many contrary chances. It is a simple matter of arithmetic to show the number of absurdities against which the theorists rush headlong.

Nor is this all. We should have to ask ourselves how casual actions, to which the insect was not predisposed by nature, can become the source of a hereditary transmissible habit. We should look upon a man as a sorry wag who came to us and said that the descendant of the desnucador knows the art of slaughtering cattle from A to Z merely through being the son of his father, without the aid of precept or example. The father does not use his blade just once or twice, by accident; he operates every day and scores of times a day; he goes to work with reflection. It is his business. Does this lifelong practice create a transmissible habit? Are the sons, the grandsons, the great-grandsons any the wiser, without instruction? No, the thing has to start afresh each time. Man is not predisposed by nature to this butchery.

If, on her side, the Wasp excels in her art, it is because she is born to follow it, because she is endowed not only with tools, but also with the knack of using them. And this gift is original, perfect from the outset: the past has added nothing to it, the future will add nothing to it. As it was, so it is and will be. If you see in it naught but an acquired habit, which heredity hands down and improves, at least explain to us why man, who represents the highest stage in the evolution of your primitive plasma, is deprived of the like privilege. A paltry insect bequeaths its skill to its offspring; and man cannot. What an immense advantage it would be to humanity if we were less liable to see the worker succeeded by the idler, the man of talent by the idiot! Ah, why has not protoplasm, evolving by its own energy from one being into another, reserved until it came to us a little of that wonderful power which it has bestowed so lavishly upon the insects! The answer is that apparently, in this world, cellular evolution is not everything.

For these among many other reasons, I reject the modern theory of instinct. I see in it no more than an ingenious game in which the armchair naturalist, the man who shapes the world according to his whim, is able to take delight, but in which the observer, the man grappling with reality, fails to find a serious explanation of anything whatsoever that he sees. In my own surroundings, I notice that those who are most positive in the matter of these difficult questions are those who have seen the least. If they have seen nothing at all, they go to the length of rashness. The others, the timid ones, know more or less what they are talking about. And is it not the same outside my modest environment?

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