Popular Science Monthly/Volume 11/September 1877/Instinct and Intelligence
By W. K. BROOKS.
TO many persons the phenomena of instinct and intelligence in animals seem irreconcilable with any theory of the evolution of organisms through the action of natural causes, but the popular opinion upon this subject has undergone a very considerable change within the last half-century, so that the difficulty now presents itself and finds expression in a much more manageable form than would have been the case a few years since.
With regard to instinct, we can easily see that if animals of a given species are born with a constitutional tendency, or instinct, to perform a certain action under certain circumstances, this tendency may be improved and perfected by natural selection, provided favorable variations appear, and be inherited. If instinct varies in the different individuals of a species, the struggle for existence wall result in the destruction of those in which it is imperfectly or abnormally developed, and the preservation of those individuals which exhibit any advantageous variation.
In order to place the phenomena of instinct upon the same footing, with reference to natural selection, as is held by other manifestations of life, it is only necessary to show that instincts vary, and that these variations may become hereditary.
Not a great many years ago the statement that instinct varies among animals of the same species would have been met by a flat denial, but no one at all acquainted with the subject would probably now be found to dispute it. A few examples may not be out of place, however.
The oriole now builds its hanging-nest with the pieces of string, horse-hair, yarn, and carpet-ravelings, which are to be found in abundance about houses and barns; and I have seen a nest into which three fish-lines, with their hooks and sinkers, several yards of kite-tail from a telegraph wire, and a shoe-string, were interwoven. Of course, it is not natural for the bird to use such material as this, but the odds and ends furnished by man are much better fitted to its needs than the grass and fibres used by its less civilized ancestors. This change certainly shows power to improve in accordance with changed conditions; but it may perhaps be said that it is not an example of change in an instinct, but simply in a non-hereditary habit. The fear of man, shown by almost all the smaller animals, is in many cases newly acquired, for in regions uninhabited by man it is not shown, and it is only as the animals of such regions learn, by generations of persecution, that man is highly and peculiarly dangerous, that they come to avoid him; yet this fear is truly instinctive, for it is shown by the young as well as by the adult. The testimony of travelers as to the tameness of animals in regions where they have never been persecuted, is well known. For instance, Darwin, in his "Journal" of the voyage of the Beagle, says: "This disposition is common to all the terrestrial species of the Galapagos Islands, namely, to the mocking-thrush, the finches, wrens, tyrant fly-catchers, the dove, and carrion-buzzard.All of them often approached sufficiently near to be killed with a switch, and sometimes, as I myself tried, with a cap or hat. A gun here is almost superfluous, for with the muzzle I pushed a hawk off the branch of a tree. One day, while lying down, a mocking-thrush alighted on the edge of a pitcher made of the shell of a tortoise, which I held in my hand, and began very quietly to sip the water; it allowed me to lift it from the ground, while seated on the vessel. I often tried and very nearly succeeded in catching these birds by their legs. Formerly these birds appear to have been even tamer than at present. Cowley (in the year 1684) says that 'the turtledoves were so tame that they would often alight upon our hats and arms, so that we could take them alive, they not fearing man until such time as some of our company did fire upon them, whereby they were rendered more shy.' Dampier also, in the same year, says that a man in a morning's walk might kill six or seven dozen of these doves. At present, although certainly very tame, they do not alight upon people's hats, nor do they suffer themselves to be killed in such large numbers. It is surprising that they have not become wilder; for these islands, during the last hundred and fifty years, have been much visited by buccaneers and whalers; and the sailors, wandering through the woods in search of tortoises, take a cruel delight in knocking down the little birds."
Darwin also says that at Terra del Fuego a certain species of goose, which is much hunted by the natives, is so wild that it is a very difficult matter to kill even one, although in the Falkland Islands, where it is not often disturbed by man, a sportsman may sometimes kill more in a day than he can carry home. This goose is not migratory; but a bird of passage, the black-necked swan, brings with it to the Falkland Islands the wisdom learned in more dangerous regions, and is very hard to obtain. Darwin ends with the following comments: "From these several facts we may, I think, conclude, first, that the wildness of birds with regard to man is a particular instinct directed against him, and not dependent on any general degree of caution arising from other sources of danger; secondly, that it is not acquired by individual birds in a short time, even when much persecuted, but in the course of successive generations it becomes hereditary. With domesticated animals we are accustomed to see new mental habits or instincts acquired, and rendered hereditary; but with animals in a state of nature it must always be most difficult to discover instances of acquired hereditary knowledge. In regard to the wildness of birds there is no way of accounting for it except as an inherited habit; comparatively few young birds, in any year, have been injured by man in England, yet all, even nestlings, are afraid of him; many individuals, on the other hand, both at the Galapagos and at the Falklands, have been pursued and injured by man, but yet have not learned a salutary fear of him." If instincts have been acquired gradually by natural selection—like modifications of structure—we should expect to find that, like other adaptations, they are in many cases more or less imperfect. We were formerly taught that instinct differs from intelligence inasmuch as it is an infallible guide and perfect in its results. If we have shown that it admits of improvement, we need not argue its imperfection; but a few examples of the failure of instinct may not be out of place. Migratory birds often return too early in the season, and perish from lack of food. The instinct which leads insects to lay their eggs upon or near food which is proper for the larvæ to which the eggs will in time give rise, although the adult insect may feed upon something quite different, is a very wonderful and beautiful provision of Nature, but it has been shown to fail signally in some cases. Certain flies lay their eggs upon decaying animal matter, in order that the maggots may find an abundant supply of proper food; but the flies are sometimes misled by the odor of a species of arum, and lay their eggs upon the leaves of the plant. The young, of course, perish as soon as they are hatched, for they are unable to subsist upon vegetable food. The presence of a certain odor stands in relation to the existence of putrid flesh, and there is in the fly a corresponding relation between the sensation caused by this odor and a tendency to deposit her eggs. That is, the relation between a certain sensation and a certain action is in harmony with another relation between two phenomena, external to the fly; but this adjustment is not quite perfect, since the odor of the arum-plant, which is not the right odor, does what nothing but the odor of putrid meat should do.
The trap-door spider makes for its dwelling a round hole in the ground, which it lines with silk and covers with a lid or trap-door, fastened with a hinge and lying even with the ground, and fitting so exactly that it is no easy matter to find the hole, even when the animal has just been seen to enter it. To render the deception still more perfect, the top of the door is sometimes covered with living mosses and lichens, which the spider is supposed to plant in this place; the whole apparatus is very wonderfully made, and we can hardly admire sufficiently the instinct which enables the animal to construct it. This instinct may lead to a great mistake, for a close observer of the habits of this animal—J. T. Moggidge—found a nest in sandy soil, where there was no vegetation. The lid had its usual cover of moss, although this failed to answer its purpose, for the little round spot of verdure made the nest very conspicuous instead of helping to hide it. The process of fish-culture furnishes a good illustration of the imperfection of such highly-important instincts as those concerned with the perpetuation of the species. It is found that if trout, white-fish, shad, or many other species, are allowed to lay their eggs in the natural manner, a very great proportion—usually much more than half—fail to be fertilized, and of the remainder many are destroyed by crowding and lack of fresh water; many more are buried by sediment, or carried away by the current, so that only a very few develop and give rise to young fish; and many of the young are so weakened by the unfavorable conditions to which they have been exposed that they are unable to free themselves from the remains of the egg-shell, so that the number hatched is very small indeed as compared with the number of eggs. To obviate this, the male and female fish are caught just before the time at which the eggs are deposited. These are pressed out of the body of the mother, artificially fertilized, and placed in proper hatching-boxes, and in this way the number of young is increased many hundred per cent. It is no exaggeration to say that, as compared with the artificial, the natural method of propagation among these fishes is crude and faulty in the greatest degree. Nor can it be said that this wastefulness is compensated by the great number of eggs, for the production of so many eggs by the mother involves a great expenditure of force, which might be saved by more highly-developed instincts.
In view of all the instances given, I think we may conclude that instinct is not a fixed, immutable, perfect law and guide, but an imperfect, improvable, gradually-acquired method of adjusting actions to the surrounding conditions; and therefore subject to slow perfection through the survival of the fittest variations. Let us now see whether animals possess other mental powers than the instinctive; whether they exhibit any faculty which may properly be called intelligence. No one doubts that most of our domestic animals admit of individual improvement or education, but it may be said that this improvement is due to man's intelligence, not to that of the animals themselves. There is abundant proof, however, that animals are capable of much individual improvement in a state of nature. You can't catch old birds with chaff; and a new trap partakes of the properties of a new broom, Morgan, in his book on "The American Beaver and his Works," says that beaver-houses are often found of a construction very inferior to the average; and that, according to the Indians, these are the work of young animals which have not yet completed their education. Every one who has studied the habits of cats knows how frequently they fail to raise their first litter of kittens, and a very careful observer tells me that this is true of white mice to a much greater degree.
Leroy, a writer of the seventeenth century, and a very reliable authority, says that there is a marked inferiority in the nests made by young birds, and that the best and most complicated nests are made by those species of birds whose young remain a long time in the nest, and thus have more opportunity to see how it is made.
He says that not only are the nests of young birds badly made, but that very unfit places are chosen for them, and that these defects are remedied in time when the builders have been instructed by their sense of the inconvenience they have endured. Wilson likewise claimed that there is a very perceptible inferiority in the nests of young birds. To one at all familiar with animals, the fact that each individual undergoes a process of intellectual development and self-education is so familiar that it seems strange that any one should question it; but, as the contrary statement is still occasionally met with, it seemed proper to give the above instances of improvement.
The fact that dogs dream, and under circumstances of peculiar hardship and misfortune become crazy, seems to indicate a very close similarity between their minds and ours; and no one who has seen an idiotic or half-witted dog can doubt that an ordinary dog has a mind to lose.
Dr. Kane tells us that one of the Newfoundland dogs which spent two arctic winters with him was so oppressed by the darkness and solitude of the long night, and so reduced in strength by hardship and cold, that it at last became insane, and manifested all the symptoms which were observed in some of the human beings of the party who were affected in the same way by the same causes.
Many animals, poultry for instance, have special cries for special purposes: an alarm-cry to indicate danger; a call to announce the discovery of a supply of food; a maternal "cluck" to keep the brood of chicks together; and several other cries, each of which has a meaning. These cries are undoubtedly produced and understood by the fowls instinctively, but the process by which man learns to recognize them and to understand their meaning is purely intellectual. The farmer's dog learns to distinguish and understand them as well as the farmer himself, and knows when he may be unconcerned, and when he is to go to their defense; and there is not the slightest reason to doubt that he acquires his knowledge, as man does, by a process of observation, memory, and thought. Instances of intelligence among the higher mammalia could, of course, be indefinitely multiplied, but it does not seem necessary to dwell upon the subject here. I will, however, give a few examples of what seems to be intelligence among the lower animals. I think it was Lubbock who observed a spider which wished to raise a captured wasp to a more elevated portion of the web. Finding it too heavy, it stopped its efforts and gnawed off two of the wings, and then made a second attempt. As it was still too heavy, it lightened it still further, and again tested it, and repeated the process until it had reduced its load to a manageable size. I am unable to give the authority for the following, but think the account was published in Nature some years since: A gentleman found a small dead bird and impaled it upon a stick, and stuck the other end of the stick into the ground near some "scavenger" beetles. The instinct which leads these insects to bury dead birds and other animals as a provision for the wants of their young is well known. In this case they soon found the bird—but how was a bird perched upon an upright stick to be buried in the ground? After some consultation they resorted to the very clever expedient of digging up the stick, and then digging a hole large enough to bury both bird and stick. Although this seems very like intelligence, it may possibly be explained as a case in which the ordinary instinctive habit of the animal accidentally fitted an exceptional demand upon it.
Many of the actions of ants, however, do not admit of any such interpretation. When two armies of ants of different species leave their homes at the same time, arrange themselves in ranks, and march to a point of meeting, and engage in battle, they exhibit, not simply proofs of concerted action, but evidences that they can arrange and plan to meet extraordinary and unusual emergencies.
Of the actions which organisms perform in order to accomplish a purpose, some, like those to which I have called your attention, are to be placed above, others below instinct. Many of the actions of plants, such as turning the leaves toward the light, the tendency of the roots to grow downward, and. the closure of the flowers at night, remotely resemble instinctive actions. In some the resemblance is more perfect—he groping of tendrils for support, for instance. Prof. Gray gives the following account of this action: "When a twining stem overtops its support, the lengthening shoot is seen thrown over to one side, and usually outstretched. One might suppose that it had fallen over by its weight, but it is not generally so. If turned over, say to the north, when first observed, it will probably be found reclining to the south an hour or two later, and, an hour later again, turned northward: that is, the end of the stem sweeps round in a circle continually like the hand of a clock. It keeps on growing as it revolves; but the revolving has nothing to do with the growth, and indeed is often so rapid that several complete turns may be made before any increase in length could be observed. The time of revolving varies in different species. It also depends upon the weather—being slow or imperceptible when it is cold, and more rapid when it is warmer. Sometimes it stops when everything seems favorable, and starts again after a while. The hop, bean, and morning-glory, are as quick as any. In a sultry day, and when in full vigor, they commonly sweep round the circle in less than two hours. They move by night as well as by day. This sweeping is the cause of the twining. The stem sweeps round in order that it may reach some neighboring support; as it grows it sweeps a wider and wider space, that is, reaches farther and farther out. When it strikes against any solid body, like the stalk of a neighboring plant, it is stopped; but the portion beyond the contact is free to move as before, and, continuing to move on and to lengthen, it necessarily winds itself round the support, that is, twines." The sudden closure of the leaf of the Venus's-flytrap, as soon as it is touched by an insect, and the excitement of the glandular hairs upon its surface, still more closely resemble the instinctive actions of animals, and we here find the power to distinguish between different foreign bodies, for Darwin has shown that, although the leaf will close upon a small piece of meat, it is not excited by contact with a small piece of glass. In animals we meet with a large class of what are called reflex or automatic actions, and these are perhaps a little nearer to true instinctive actions than most of those performed by plants. Such are the actions of the various organs concerned in digestion, which are passive until the presence of food calls them into action, when they at once begin their work. A little higher are those actions which may be performed or controlled by volition, although they are usually automatic; such as winking to protect the eye from injury, and the act of throwing out the arms when in danger of falling. These are commonly spoken of as instinctive actions, but it is impossible to separate them from the class last spoken of. A little higher than the reflex actions are the truly instinctive ones, as a type of which we may take the actions of some very young chickens, experimented upon by Mr. Spalding. In a paper read before the British Association, this experimenter says: "Chickens hatched and kept in the dark for a day or two, on being placed in the light nine or ten feet from a box in which a brooding hen was concealed, after standing chirping for a minute or two, uniformly set off straight to the box, in answer to the call of the hen, which they had never seen, and never before heard. This they did, struggling through grass, and over rough ground, when not able to stand steadily on their legs. Again, a young hawk was made to fly over a hen with her first brood of chickens, then about a week old. In the twinkling of an eye most of the chickens were hid among the grass and bushes; and scarcely had the hawk touched the ground, about twelve yards from where the hen had been sitting, when she fell upon it, and would soon have killed it outright. A young turkey gave even more striking evidence. When ten days old it heard the voice of the hawk for the first time, and close beside it. Like an arrow from a bow it darted off in the opposite direction, and crouched in a corner, and remained for ten minutes motionless and dumb with fear." These examples will serve as illustrations of pure instinct, and we will pass now to actions which are superior, but obviously similar, to the instinctive ones. Actions which are frequently repeated become habitual, and habits of long standing become so firmly fixed that the actions are performed unconsciously, and, as it were, instinctively.
Most of us can remember the labor and pains which were required in order to learn to write: the comparatively easy acquisition of the art of making down-strokes, and the tendency, which we adhered to so obstinately, to form all our letters with down-strokes, and to fill in the curves and shading afterward. Any one who has watched a child writing has observed the necessity under which it labors for counting the bends to distinguish an m from an n, and the tax which an hour's writing inflicts upon all its bodily and mental powers. Constant practice soon renders writing habitual, and the necessary muscles act mechanically, so that we are able to give all our attention to the intellectual part of the process, while the writing is done without any effort or attention. A well-drilled soldier performs the proper evolution at the word of command, although he may be so preoccupied or so fatigued as to be perfectly unconscious of his actions. Such habits are remarkably persistent, especially when they are acquired early in life, and they have nothing to distinguish them from instinctive actions except that they are unconscious.
They are often performed involuntarily, and even in opposition to a previous determination. Street-car horses soon learn to stop and start at the sound of the car-bell, and I once saw an obstinate horse, which had resisted every other means of persuasion, start at the sound of the bell and get the car fairly under way before he had time to think what he was doing.
Every one remembers the story of the old pensioner who received the command "Attention" from a by-stander while he was returning from market with his dinner in his hand. At the word of command lie instantly and mechanically dropped his dinner in the mud, and took the proper position. Occasionally in man, and quite frequently in other animals, these habits of long standing are transmitted to the next generation, and, as they are then independent of individual experience, they are true instincts. Although the art of writing is not inherited, the particular style of handwriting is very often hereditary. The act of pointing or setting in dogs would be a great disadvantage to wild animals, and there is every reason to believe that it has been very recently acquired by a few breeds of domestic dogs; yet it is frequently inherited in its highly-developed form, and the transmission of a slight tendency in this direction appears to be general. The following seems to be an instance of the appearance in the second generation, as an instinct, of an acquired habit. A correspondent of Nature says:
"A few years ago I bought in Skye a perfectly uneducated Skye-terrier. The first accomplishment which I taught him was that of 'sitting up'—an accomplishment which he had great difficulty in acquiring. This was not owing to any stupidity on his part, for when he had once passed over this pons asinorum of dog-performances, he proved to be a very clever animal, and learned many other tricks with great ease. He appears never to have forgotten the pains which were taken to teach him his first trick, and to have judged therefrom that there is great merit in sitting up. Not only does he rely upon this as a last resource to move me to take him out, or not to whip him, but he judges that it must soften the heart of an India-rubber ball. Sometimes, when annoyed at his playing with this, his favorite plaything, I have placed it on a chimney-piece, and turned ray attention elsewhere.
"On looking round again, I have seen my dog sitting up to the India-rubber ball, evidently hoping that it would jump down and play with him again. My dog is now the father of a family, and one of his daughters, who has never seen her father, is in the constant habit of sitting up, although she has never been taught to do so, and has never seen others sit up. She is especially given to this performance when any other dog is being scolded."Whether this is an instance of helping a fellow-animal, of which Mr. Darwin gives so many curious examples, or whether the dog simply hopes to avert the storm from her own head, the fact appears to me patent that this dog has inherited the impression that sitting up has some special virtue for turning away wrath."
A little higher than the habitual actions are those which are so complicated, or occur so rarely, or depend upon such delicate combinations of conditions, that they never become habitual—that is, they are never performed without thought, although we may be able to group them into classes, and to guide our conduct by general rules or principles, either established by experience or accepted upon the authority of others. The resemblance between these actions and the instinctive ones is recognized in common speech, for we often hear it said of a person who is guided in the main, in this way, by general rules, and is often unable to assign any reason for a particular course of conduct, that he or she is a person of fine natural instincts.
The actions of the sailor, who guides his movements by the weather reports from the Government Signal-Office, without understanding or caring much about the way in which the reports are made out, are still more rational, and further removed from instinct, although they evidently fall into the series, and have much in common with those actions last mentioned. Finally, the actions of "Old Probabilities" himself belong to a still higher class, and are eminently rational.
Reviewing the ground which we have passed over, we find that living things present us with a series of more or less related actions.
First, we have the mechanical and reflex actions of plants and animals; then the instinctive action, then the hereditary habit, then the acquired habit; next the action governed by a general rule, established by experience; and finally the rational action.
Great as seems to be the difference between the two extremes of this series when considered by themselves, it is possible to pass from one to the other through a series of intermediate actions, without the necessity for any great jump in any part of the series; and it is plain that, great as are the differences between them, they all have something in common. Let us try to discover what this something is. All the actions which we have been examining are alike in this, that they are directed to the accomplishment of a purpose. The root grows downward in order that it may reach water. The leaf turns with the sun in order that it may receive a greater supply of heat. The fly-trap closes upon its prey and pours forth its secretion in order that it may be supplied with food. The vine twines in order that its long, slender stem may be supported. The digestive organs perform their various functions that the body may be nourished and its waste supplied. The eyelids close in order that the eye may be shielded from danger.
The chick instinctively seeks its mother that it may be protected and fed; and it hides from the hawk to save its life. The dog begs and the soldier goes through his manual to escape punishment, or to gain a reward or approbation, or perhaps from a combination of all these motives with still higher ones, but in any case to accomplish a purpose. The sailor watches the weather-predictions and regulates his actions accordingly, in order that his voyage may be finished as safely and quickly as possible. And the signal-officer publishes his predictions in order that the public may be informed as to the probabilities of change.
It may be said that in the last two or three cases the purpose is intelligently appreciated, and that they are thus separated by a sharp line from the others; but this distinction gradually shades off and disappears as an action becomes habitual, and as soon as the habit becomes hereditary it may be entirely wanting.
The well-drilled soldier goes through with his evolutions without a thought as to his reasons for doing so, and nearly every middle-aged business-man of methodical habits probably recollects finding himself at his place of business on a holiday without knowing how or why he came there. One characteristic of these various actions is, then, that each has a purpose. Another is that, although the object of the action is the accomplishment of a purpose, the cause of the action is a change, external to the organism and distinct from the purpose.
The leaf of the Venus's-flytrap closes, and the digestive organs of an animal do their work, not because food is needed, but because they are excited by the presence of a foreign body. The dog points because he scents a particular odor, not because he wishes to do his duty. The soldier assumes his position because he hears the word of command, etc. The actions which are the subject of our present lecture stand, then, in a double relationship. They are excited by certain external changes, and they have for their object the accomplishment of a purpose. Herbert Spencer has expressed this dual relationship in a simple formula. According to him, these and all other peculiarly vital actions consist in "the adjustment of internal relations to external relations." This is not very lucid when stated abstractly, but perhaps an example will help to make it clear. If I kick a stone, I may move it a greater or less distance, and set up some slight molecular change within it, and hurt my foot, perhaps. If I kick a dead dog, the result is the same; but, if the dog is alive, I shall find that all these results follow, and something more. The molecular change in the nerves of the dog gives rise to or excites a series of actions adapted to meet my attack and to prevent further injury. There is a relation, external to the dog, between the kick and a disposition to do him further violence; and there is an internal relation in the dog between the sensation caused by the blow and a desire to escape the violence which is to follow; and whether he crouches and supplicates, or puts his tail between his legs and runs, or returns my attack, he simply adjusts internal relations to external relations. There is a relation between a downward direction and the presence of water in the ground, and to this relation the roots of the plant respond.
There is a relation between the presence of a foreign body in the stomach and food to be digested; and accordingly, when the stomach is excited by the sensation of contact with a foreign body, it begins its work—that is, there is an adjustment between the internal relation of a certain sensation to the digestive process and the external relation between the presence of foreign matter in the stomach and food.
There is a relation between the sudden approach of a body toward the eye and danger to that organ, and to this relation the nerves and muscles are adjusted. There is a relation between a peculiar "cluck" and the presence of the mother-hen, and to this relation the chick responds. There grows up in the mind of the soldier a connection between the word "attention" and a particular attitude, and when he feels the sensation caused by the command, he at once, and unconsciously, performs the muscular movements necessary to assume that position; that is, there is an adjustment between the internal relation of a certain sensation to certain muscular movements and the external relation of a certain command to the necessity for assuming a given position. The sailor learns that there is a relation between certain signals and stormy weather, and to this relation his actions are adjusted. Finally, General Meyer finds that there is a relation between low barometric pressure in certain parts of the country and a liability to storms in other regions, and to this external relation he adjusts his actions.
The kind of external change to which an organism may respond of course varies greatly in different cases, both in constancy and complexity. The Venus's-flytrap is adjusted only to relations between objects on the surface of the leaf and in contact with it, but an animal with even rudimentary organs of sense may respond to changes which occur at a distance. Even the simple capacity to distinguish light from darkness is enough to enable an animal to perceive a distant body between it and the sun, and to adjust its actions accordingly.
As we ascend to creatures having more developed eyes, we find an increase in the sphere of surrounding space throughout which external relations can establish corresponding internal relations. A slight convexity of the epidermic layer lying over the sensitive tract first serves, by concentrating the rays, to render appreciable less marked variations in the quantity of light, and thus brings into view the same bodies at a greater distance, and smaller or less opaque bodies at the same distance. From this point upward, through the various types of aquatic creatures to the higher air-breathing creatures, we trace, under various forms and modifications, a complicated visual apparatus and a widening space through which the correspondence extends. It is needless to go into details. Hypotheses and illustrations aside, it is obvious that from the polyp, which does not stir till touched, up to the telescopic-eyed vulture or the far-sighted Bushman, one aspect of progressing life is the greater and greater remoteness at which visible relations in the environment produce adapted relations in the organism. The extension of the correspondence in space does not end with the perfecting of the senses. In creatures of comparatively advanced organization there arise powers of adjusting inner relations to outer relations that are far too remote for direct perception. The motions by which a carrier-pigeon finds its way home, though taken a hundred miles away, cannot be guided by sight, smell, or hearing, in their direct and simple forms. Chased animals, that make their way across the country to places of refuge out of view, are obviously led by combinations of past and present impressions which enable them to transcend the sphere of sense. And thus also must it be with creatures which annually migrate to other lands.
In man, this secondary process of extension is carried still further, Though the correspondences he effects by immediate perception have a narrower range than those of some inferior creatures, and though in that species of indirect adjustment just exemplified he is behind sundry wild and domesticated animals, yet, by still more indirect means, he adjusts internal relations to external relations that are immensely beyond the appreciation of lower beings. By combining his own perceptions with the perceptions of others as registered in maps, he can reach special places lying thousands of miles away over the earth's surface. A ship, guided by compass, and stars, and chronometer, brings him from the antipodes information by which his purchases here are adapted to prices there. From the characters of exposed strata he infers the presence of coal below, and thereupon adjusts the sequences of his actions to coexistences a thousand feet underneath. Nor is the environment through which his correspondences reach limited to the surface and the substance of the earth. It stretches into the surrounding sphere of infinity. It was extended to the moon when the Chaldeans discovered how to predict eclipses; to the sun and nearer planets when the Copernican system was established; to the remoter planets when an improved telescope disclosed one, and calculation fixed the position of the other; to the stars when their parallax and proper motion were measured; and, in a vague way, even to the nebulae when their composition and forms of structure were ascertained. At first sight, no two things could seem to have less in common than the tendency of a sprouting potato to grow toward the light, and the preparations made by human beings for such a rare, and distant, and complicated event as a transit of Venus; yet each is, objectively considered, an adjustment of internal relations to external relations, and the two phenomena are so well connected by intermediate forms that there can be no doubt of their relationship.
Physiologists are gradually proving the statement that these and all other vital changes are, in ultimate analysis, changes in the protoplasm of the body, and that they are not brought about by any peculiar vital force, but are the direct outcome of the physical and chemical structure of the protoplasm itself; so that vital changes, considered simply as changes, must not be regarded as peculiar, and fundamentally unlike the changes of inorganic matter.
Vital changes cannot, however, be regarded as changes simply standing by themselves, for, if we overlook their adjustment to the accomplishment of a purpose, we omit their most essential characteristic.
In so far as the contraction of a muscle is simply a change, it is without doubt purely physical; but in the adjustment of this change to a relation between external changes, in its adaptation to a purpose, we have something which has no parallel except in living things, and perhaps some of man's contrivances, such as the automatic governor of the steam-engine. Living things are distinguished from those which have not life by their adjustment, and life consists in this adjustment. Small as this difference seems when stated abstractly, and unimportant as it appears to be when we contrast such an organism as an amœba, with its simple and almost mechanical power of retracting its pseudopodia upon irritation, and such a highly-complex and changeable inorganic being as the ocean, yet, considered not in itself but in its adjustment to external relations, this power in the amoeba separates it very widely from all inorganic forms of existence, and connects it with the highest manifestations of life; for the series of adjustments of which that of the amœba is one of the simplest may be traced almost without break up to the most rational actions of man. A vorticella contracts and folds down its circlet of cilia when touched, because there is a connection between violent contact and the presence of danger; and this recognition of a connection between the changes of the external world is knowledge of the order of Nature, and this, in its higher form, is experience, and experience implies memory, and memory and experience are forms of consciousness. Thus we are able to understand the meaning of such expressions as that of Haeckel, that living things are distinguished from the not living by the possession of memory. It seems best to restrict the use of such purely subjective terms as memory and experience to the higher forms of conscious life, but we must not overlook the fact that the existence of an adjustment between internal and external relations implies something fundamentally like the memory of higher animals.
Finally, I wish to call attention to the fact that natural selection is constantly acting through the law of the survival of the fittest, in such a way as to bring each organism into more and more perfect harmony with its environment; that is, it is constantly bringing about a more and more exact, definite, and perfect adjustment between external and internal relations. If this adjustment constitutes vitality, and if natural selection furnishes an explanation of the manner in which the adjustment has been brought about, have we not, in the law of natural selection, an explanation of the origin of life?—not of course of the origin of the matter of life, nor of the changes of which life is made up, nor of the production of living beings, but of the origin of those attributes by which living things are especially characterized, and in which they differ from all other forms of existence.