When we see the animals going about, living their lives in many ways as we live ours, seeking their food, avoiding their enemies, building their nests, digging their holes, laying up stores, migrating, courting, playing, fighting, showing cunning, courage, fear, joy, anger, rivalry, grief, profiting by experience, following their leaders, ­when we see all this, I say, what more natural than that we should ascribe to them powers akin to our own, and look upon them as thinking, reasoning, and reflecting. A hasty survey of animal life is sure to lead to this conclusion. An animal is not a clod, nor a block, nor a machine. It is alive and self-directing, it has some sort of psychic life, yet the more I study the subject, the more I am persuaded that with the probable exception of the dog on occasions, and of the apes, animals do not think or reflect in any proper sense of those words. As I have before said, animal life shows in an active and free state that kind of intelligence that pervades and governs the whole organic world, ­intelligence that takes no thought of itself. Here, in front of my window, is a black raspberry bush. A few weeks ago its branches curved upward, with their ends swinging fully two feet above the ground; now those ends are thrust down through the weeds and are fast rooted to the soil. Did the raspberry bush think, or choose what it should do? Did it reflect and say, Now is the time for me to bend down and thrust my tip into the ground? To all intents and purposes yes, yet there was no voluntary mental process, as in similar acts of our own. We say its nature prompts it to act thus and thus, and that is all the explanation we can give. Or take the case of the pine or the spruce tree that loses its central and leading shoot. When this happens, does the tree start a new bud and then develop a new shoot to take the place of the lost leader? No, a branch from the first ring of branches below, probably the most vigorous of the whorl, is promoted to the leadership. Slowly it rises up, and in two or three years it reaches the upright position and is leading the tree upward. This, I suspect, is just as much an act of conscious intelligence and of reason as is much to which we are so inclined to apply those words in animal life. I suppose it is all foreordained in the economy of the tree, if we could penetrate that economy. It is in this sense that Nature thinks in the animal, and the vegetable, and the mineral worlds. Her thinking is more flexible and adaptive in the vegetable than in the mineral, and more so in the animal than in the vegetable, and the most so of all in the mind of man.

The way the wild apple trees and the red thorn trees in the pasture, as described by Thoreau, triumph over the cattle that year after year browse them down, suggests something almost like human tactics. The cropped and bruised tree, not being allowed to shoot upward, spreads more and more laterally, thus pushing its enemies farther and farther away, till, after many years, a shoot starts up from the top of the thorny, knotted cone, and in one season, protected by this cheval-de-frise, attains a height beyond the reach of the cattle, and the victory is won. Now the whole push of the large root system goes into the central shoot and the tree is rapidly developed.

This almost looks like a well-laid scheme on the part of the tree to defeat its enemies. But see how inevitable the whole process is. Check the direct flow of a current and it will flow out at the sides; check the side issues and they will push out on their sides, and so on. So it is with the tree or seedling. The more it is cropped, the more it branches and rebranches, pushing out laterally as its vertical growth is checked, till it has surrounded the central stalk on all sides with a dense, thorny hedge. Then as this stalk is no longer cropped, it leads the tree upward. The lateral branches are starved, and in a few years the tree stands with little or no evidence of the ordeal it has passed through. In like manner the nature of the animals prompts them to the deeds they do, and we think of them as the result of a mental process, because similar acts in ourselves are the result of such a process.

See how the mice begin to press into our buildings as the fall comes on. Do they know winter is coming? In the same way the vegetable world knows it is coming when it prepares for winter, or the insect world when it makes ready, but not as you and I know it. The woodchuck “holes up” in late September; the crows flock and select their rookery about the same time, and the small wood newts or salamanders soon begin to migrate to the marshes. They all know winter is coming, just as much as the tree knows, when in August it forms its new buds for the next year, or as the flower knows that its color and perfume will attract the insects, and no more. The general intelligence of nature settles all these and similar things.

When a bird selects a site for its nest, it seems, on first view, as if it must actually think, reflect, compare, as you and I do when we decide where to place our house. I saw a little chipping sparrow trying to decide between two raspberry bushes. She kept going from one to the other, peering, inspecting, and apparently weighing the advantages of each. I saw a robin in the woodbine on the side of the house trying to decide which particular place was the best site for her nest. She hopped to this tangle of shoots and sat down, then to that, she turned around, she readjusted herself, she looked about, she worked her feet beneath her, she was slow in making up her mind. Did she make up her mind? Did she think, compare, weigh? I do not believe it. When she found the right conditions, she no doubt felt pleasure and satisfaction, and that settled the question. An inward, instinctive want was met and satisfied by an outward material condition. In the same way the hermit crab goes from shell to shell upon the beach, seeking one to its liking. Sometimes two crabs fall to fighting over a shell that each wants. Can we believe that the hermit crab thinks and reasons? It selects the suitable shell instinctively, and not by an individual act of judgment. Instinct is not always inerrant, though it makes fewer mistakes than reason does. The red squirrel usually knows how to come at the meat in the butternut with the least gnawing, but now and then he makes a mistake and strikes the edge of the kernel, instead of the flat side. The cliff swallow will stick her mud nest under the eaves of a barn where the boards are planed so smooth that the nest sooner or later is bound to fall. She seems to have no judgment in the matter. Her ancestors built upon the face of high cliffs, where the mud adhered more firmly.

A wood thrush began a nest in one of my maples, as usual making the foundation of dry leaves, bits of paper, and dry grass. After the third day the site on the branch was bare, the wind having swept away every vestige of the nest. As I passed beneath the tree I saw the thrush standing where the nest had been, apparently in deep thought. A few days afterward I looked again, and the nest was completed. The bird had got ahead of the wind at last. The nesting-instinct had triumphed over the weather.

Take the case of the little yellow warbler when the cowbird drops her egg into its nest ­does anything like a process of thought or reflection pass in the bird’s mind then? The warbler is much disturbed when she discovers the strange egg, and her mate appears to share her agitation. Then after a time, and after the two have apparently considered the matter together, the mother bird proceeds to bury the egg by building another nest on top of the old one. If another cowbird’s egg is dropped in this one, she will proceed to get rid of this in the same way. This all looks very like reflection. But let us consider the matter a moment. This thing between the cowbird and the warbler has been going on for innumerable generations. The yellow warbler seems to be the favorite host of this parasite, and something like a special instinct may have grown up in the warbler with reference to this strange egg. The bird reacts, as the psychologists say, at sight of it, then she proceeds to dispose of it in the way above described. All yellow warblers act in the same manner, which is the way of instinct. Now if this procedure was the result of an individual thought or calculation on the part of the birds, they would not all do the same thing; different lines of conduct would be hit upon. How much simpler and easier it would be to throw the egg out ­how much more like an act of rational intelligence. So far as I know, no bird does eject this parasitical egg, and no other bird besides the yellow warbler gets rid of it in the way I have described. I have found a deserted phoebe’s nest with one egg of the phoebe and one of the cowbird in it.

Some of our wild birds have changed their habits of nesting, coming from the woods and the rocks to the protection of our buildings. The phoebe-bird and the cliff swallow are marked examples. We ascribe the change to the birds’ intelligence, but to my mind it shows only their natural adaptiveness. Take the cliff swallow, for instance; it has largely left the cliffs for the eaves of our buildings. How naturally and instinctively this change has come about! In an open farming country insect life is much more varied and abundant than in a wild, unsettled country. This greater food supply naturally attracts the swallows. Then the protecting eaves of the buildings would stimulate their nesting-instincts. The abundance of mud along the highways and about the farm would also no doubt have its effect, and the birds would adopt the new sites as a matter of course. Or take the phoebe, which originally built its nest under ledges, and does so still to some extent. It, too, would find a more abundant food supply in the vicinity of farm-buildings and bridges. The protected nesting-sites afforded by sheds and porches would likewise stimulate its nesting-instincts, and attract the bird as we see it attracted each spring.

Nearly everything an animal does is the result of an inborn instinct acted upon by an outward stimulus. The margin wherein intelligent choice plays a part is very small. But it does at times play a part ­perceptive intelligence, but not rational intelligence. The insects do many things that look like intelligence, yet how these things differ from human intelligence may be seen in the case of one of our solitary wasps, ­the mud-dauber, ­which sometimes builds its cell with great labor, then seals it up without laying its egg and storing it with the accustomed spiders. Intelligence never makes that kind of a mistake, but instinct does. Instinct acts more in the invariable way of a machine. Certain of the solitary wasps bring their game ­spider, or bug, or grasshopper ­and place it just at the entrance of their hole, and then go into their den apparently to see that all is right before they carry it in.

Fabre, the French naturalist, experimented with one of these wasps, as follows: While the wasp was in its den he moved its grasshopper a few inches away. The wasp came out, brought it to the opening as before, and went within a second time; again the game was removed, again the wasp came out and brought it back and entered her nest as before. This little comedy was repeated over and over; each time the wasp felt compelled to enter her hole before dragging in the grasshopper. She was like a machine that would work that way and no other. Step must follow step in just such order. Any interruption of the regular method and she must begin over again. This is instinct, and the incident shows how widely it differs from conscious intelligence.

If you have a tame chipmunk, turn him loose in an empty room and give him some nuts. Finding no place to hide them, he will doubtless carry them into a corner and pretend to cover them up. You will see his paws move quickly about them for an instant as if in the act of pulling leaves or mould over them. His machine, too, must work in that way. After the nuts have been laid down, the next thing in order is to cover them, and he makes the motions all in due form. Intelligence would have omitted this useless act.

A canary-bird in its cage will go through all the motions of taking a bath in front of the cup that holds its drinking-water when it can only dip its bill into the liquid. The sight or touch of the water excites it and sets it going, and with now and then a drop thrown from its beak it will keep up the flirting and fluttering motion of its tail and wings precisely as if taking a real instead of an imaginary bath.

Attempt to thwart the nesting-instinct in a bird and see how persistent it is, and how blind! One spring a pair of English sparrows tried to build a nest on the plate that upholds the roof of my porch. They were apparently attracted by an opening about an inch wide in the top of the plate, that ran the whole length of it. The pair were busy nearly the whole month of April in carrying nesting-material to various points on that plate. That big crack or opening which was not large enough to admit their bodies seemed to have a powerful fascination for them. They carried straws and weed stalks and filled up one portion of it, and then another and another, till the crack was packed with rubbish from one end of the porch to the other, and the indignant broom of the housekeeper grew tired of sweeping up the litter. The birds could not effect an entrance into the interior of the plate, but they could thrust in their nesting-material, and so they persisted week after week, stimulated by the presence of a cavity beyond their reach. The case is a good illustration of the blind working of instinct.

Animals have keen perceptions, ­keener in many respects than our own, ­but they form no conceptions, have no powers of comparing one thing with another. They live entirely in and through their senses.

It is as if the psychic world were divided into two planes, one above the other, ­the plane of sense and the plane of spirit. In the plane of sense live the lower animals, only now and then just breaking for a moment into the higher plane. In the world of sense man is immersed also ­this is his start and foundation; but he rises into the plane of spirit, and here lives his proper life. He is emancipated from sense in a way that beasts are not.

Thus, I think, the line between animal and human psychology may be pretty clearly drawn. It is not a dead-level line. Instinct is undoubtedly often modified by intelligence, and intelligence is as often guided or prompted by instinct, but one need not hesitate long as to which side of the line any given act of man or beast belongs. When the fox resorts to various tricks to outwit and delay the hound (if he ever consciously does so), he exercises a kind of intelligence, ­the lower form which we call cunning, ­and he is prompted to this by an instinct of self-preservation. When the birds set up a hue and cry about a hawk or an owl, or boldly attack him, they show intelligence in its simpler form, the intelligence that recognizes its enemies, prompted again by the instinct of self-preservation. When a hawk does not know a man on horseback from a horse, it shows a want of intelligence. When a crow is kept away from a corn-field by a string stretched around it, the fact shows how masterful is its fear and how shallow its wit. When a cat or a dog, or a horse or a cow, learns to open a gate or a door, it shows a degree of intelligence ­power to imitate, to profit by experience. A machine could not learn to do this. If the animal were to close the door or gate behind it, that would be another step in intelligence. But its direct wants have no relation to the closing of the door, only to the opening of it. To close the door involves an after-thought that an animal is not capable of. A horse will hesitate to go upon thin ice or upon a frail bridge, even though it has never had any experience with thin ice or frail bridges. This, no doubt, is an inherited instinct, which has arisen in its ancestors from their fund of general experience with the world. How much with them has depended upon a secure footing! A pair of house wrens had a nest in my well-curb; when the young were partly grown and heard any one come to the curb, they would set up a clamorous calling for food. When I scratched against the sides of the curb beneath them like some animal trying to climb up, their voices instantly hushed; the instinct of fear promptly overcame the instinct of hunger. Instinct is intelligent, but it is not the same as acquired individual intelligence; it is untaught.

When the nuthatch carries a fragment of a hickory-nut to a tree and wedges it into a crevice in the bark, the bird is not showing an individual act of intelligence: all nuthatches do this; it is a race instinct. The act shows intelligence, ­that is, it adapts means to an end, ­but it is not like human or individual intelligence, which adapts new means to old ends, or old means to new ends, and which springs up on the occasion. Jays and chickadees hold the nut or seed they would peck under the foot, but the nuthatch makes a vise to hold it of the bark of the tree, and one act is just as intelligent as the other; both are the promptings of instinct. But when man makes a vise, or a wedge, or a bootjack, he uses his individual intelligence. When the jay carries away the corn you put out in winter and hides it in old worms’ nests and knot-holes and crevices in trees, he is obeying the instinct of all his tribe to pilfer and hide things, ­an instinct that plays its part in the economy of nature, as by its means many acorns and chestnuts get planted and large seeds widely disseminated. By this greed of the jay the wingless nuts take flight, oaks are planted amid the pines, and chestnuts amid the hemlocks.

Speaking of nuts reminds me of an incident I read of the deer or white-footed mouse ­an incident that throws light on the limitation of animal intelligence. The writer gave the mouse hickory-nuts, which it attempted to carry through a crack between the laths in the kitchen wall. The nuts were too large to go through the crack. The mouse would try to push them through; failing in that, he would go through and then try to pull them after him. All night he or his companion seems to have kept up this futile attempt, fumbling and dropping the nut every few minutes. It never occurred to the mouse to gnaw the hole larger, as it would instantly have done had the hole been too small to admit its own body. It could not project its mind thus far; it could not get out of itself sufficiently to regard the nut in its relation to the hole, and it is doubtful if any four-footed animal is capable of that degree of reflection and comparison. Nothing in its own life or in the life of its ancestors had prepared it to meet that kind of a difficulty with nuts. And yet the writer who made the above observation says that when confined in a box, the sides of which are of unequal thickness, the deer mouse, on attempting to gnaw out, almost invariably attacks the thinnest side. How does he know which is the thinnest side? Probably by a delicate and trained sense of feeling or hearing. In gnawing through obstructions from within, or from without, he and his kind have had ample experience.

Now when we come to insects, we find that the above inferences do not hold. It has been observed that when a solitary wasp finds its hole in the ground too small to admit the spider or other insect which it has brought, it falls to and enlarges it. In this and in other respects certain insects seem to take the step of reason that quadrupeds are incapable of.

Lloyd Morgan relates at some length the experiments he tried with his fox terrier, Tony, seeking to teach him how to bring a stick through a fence with vertical palings. The spaces would allow the dog to pass through, but the palings caught the ends of the stick which the dog carried in his mouth. When his master encouraged him, he pushed and struggled vigorously. Not succeeding, he went back, lay down, and began gnawing the stick. Then he tried again, and stuck as before, but by a chance movement of his head to one side finally got the stick through. His master patted him approvingly and sent him for the stick again. Again he seized it by the middle, and of course brought up against the palings. After some struggles he dropped it and came through without it. Then, encouraged by his master, he put his head through, seized the stick, and tried to pull it through, dancing up and down in his endeavors. Time after time and day after day the experiment was repeated with practically the same results. The dog never mastered the problem. He could not see the relation of that stick to the opening in the fence. At one time he worked and tugged three minutes trying to pull the stick through. Of course, if he had had any mental conception of the problem or had thought about it at all, a single trial would have convinced him as well as would a dozen trials. Mr. Morgan tried the experiment with other dogs with like result. When they did get the stick through, it was always by chance.

It has never been necessary that the dog or his ancestors should know how to fetch long sticks through a narrow opening in a fence. Hence he does not know the trick of it. But we have a little bird that knows the trick. The house wren will carry a twig three inches long through a hole of half that diameter. She knows how to manage it because the wren tribe have handled twigs so long in building their nests that this knowledge has become a family instinct.

What we call the intelligence of animals is limited for the most part to sense perception and sense memory. We teach them certain things, train them to do tricks quite beyond the range of their natural intelligence, not because we enlighten their minds or develop their reason, but mainly by the force of habit. Through repetition the act becomes automatic. Who ever saw a trained animal, unless it be the elephant, do anything that betrayed the least spark of conscious intelligence? The trained pig, or the trained dog, or the trained lion does its “stunt” precisely as a machine would do it ­without any more appreciation of what it is doing. The trainer and public performer find that things must always be done in the same fixed order; any change, anything unusual, any strange sound, light, color, or movement, and trouble at once ensues.

I read of a beaver that cut down a tree which was held in such a way that it did not fall, but simply dropped down the height of the stump. The beaver cut it off again; again it dropped and refused to fall; he cut it off a third and a fourth time: still the tree stood. Then he gave it up. Now, so far as I can see, the only independent intelligence the animal showed was when it ceased to cut off the tree. Had it been a complete automaton, it would have gone on cutting ­would it not? ­till it made stove-wood of the whole tree. It was confronted by a new problem, and after a while it took the hint. Of course it did not understand what was the matter, as you and I would have, but it evidently concluded that something was wrong. Was this of itself an act of intelligence? Though it may be that its ceasing to cut off the tree was simply the result of discouragement, and involved no mental conclusion at all. It is a new problem, a new condition, that tests an animal’s intelligence. How long it takes a caged bird or beast to learn that it cannot escape! What a man would see at a glance it takes weeks or months to pound into the captive bird, or squirrel, or coon. When the prisoner ceases to struggle, it is probably not because it has at last come to understand the situation, but because it is discouraged. It is checked, but not enlightened.

Even so careful an observer as Gilbert White credits the swallow with an act of judgment to which it is not entitled. He says that in order that the mud nest may not advance too rapidly and so fall of its own weight, the bird works at it only in the morning, and plays and feeds the rest of the day, thus giving the mud a chance to harden. Had not the genial parson observed that this is the practice of all birds during nest-building ­that they work in the early morning hours and feed and amuse themselves the rest of the day? In the case of the mud-builders, this interim of course gives the mud a chance to harden, but are we justified in crediting them with this forethought?

Such skill and intelligence as a bird seems to display in the building of its nest, and yet at times such stupidity! I have known a phoebe-bird to start four nests at once, and work more or less upon all of them. She had deserted the ancestral sites under the shelving rocks and come to a new porch, upon the plate of which she started her four nests. She blundered because her race had had little or no experience with porches. There were four or more places upon the plate just alike, and whichever one of these she chanced to strike with her loaded beak she regarded as the right one. Her instinct served her up to a certain point, but it did not enable her to discriminate between those rafters. Where a little original intelligence should have come into play she was deficient. Her progenitors Had built under rocks where there was little chance for mistakes of this sort, and they had learned through ages of experience to blend the nest with its surroundings, by the use of moss, the better to conceal it. My phoebe brought her moss to the new timbers of the porch, where it had precisely the opposite effect to what it had under the gray mossy rocks.

I was amused at the case of a robin that recently came to my knowledge. The bird built its nest in the south end of a rude shed that covered a table at a railroad terminus upon which a locomotive was frequently turned. When her end of the shed was turned to the north she built another nest in the temporary south end, and as the reversal of the shed ends continued from day to day, she soon had two nests with two sets of eggs. When I last heard from her, she was consistently sitting on that particular nest which happened to be for the time being in the end of the shed facing toward the south. The bewildered bird evidently had had no experience with the tricks of turn-tables!

An intelligent man once told me that crabs could reason, and this was his proof: In hunting for crabs in shallow water, he found one that had just cast its shell, but the crab put up just as brave a fight as ever, though of course it was powerless to inflict any pain; as soon as the creature found that its bluff game did not work, it offered no further resistance. Now I should as soon say a wasp reasoned because a stingless drone, or male, when you capture him, will make all the motions with its body, curving and thrusting, that its sting-equipped fellows do. This action is from an inherited instinct, and is purely automatic. The wasp is not putting up a bluff game; it is really trying to sting you, but has not the weapon. The shell-less crab quickly reacts at your approach, as is its nature to do, and then quickly ceases its defense because in its enfeebled condition the impulse of defense is feeble also. Its surrender was on physiological, not upon rational grounds.

Thus do we without thinking impute the higher faculties to even the lowest forms of animal life. Much in our own lives is purely automatic ­the quick reaction to appropriate stimuli, as when we ward off a blow, or dodge a missile, or make ourselves agreeable to the opposite sex; and much also is inherited or unconsciously imitative.

Because man, then, is half animal, shall we say that the animal is half man? This seems to be the logic of some people. The animal man, while retaining much of his animality, has evolved from it higher faculties and attributes, while our four-footed kindred have not thus progressed.

Man is undoubtedly of animal origin, but his rise occurred when the principle of variation was much more active, when the forms and forces of nature were much more youthful and plastic, when the seething and fermenting of the vital fluids were at a high pitch in the far past, and it was high tide with the creative impulse. The world is aging, and, no doubt, the power of initiative in Nature is becoming less and less. I think it safe to say that the worm no longer aspires to be man.