Sensation is the effect produced on the mind when a sense organ is affected in some way by external stimuli. Sensation is the lumber of the mind, the raw material out of which are elaborated all other forms of consciousness. The chief species of sensation are those of sight, sound, smell, taste, and feeling. The original sense was feeling, and out of this sense were evolved the other four. The organs of seeing, hearing, smelling, and tasting are therefore modifications of the skin, which is the organ of original sense. The fact that in all animals, down almost to the very beginnings of life, sense organs exist, suggests that sensation may be almost, if not quite, coextensive with animal life. All mammals, birds, reptiles, amphibians, and fishes have the same special sense organs as man, and the organs of sight, sound, taste, and smell occupy in all vertebrates the same relative positions in the head. Birds see better than any other animals, and carnivora smell better. Ruminants see, hear, and smell with great acuteness. Fishes also see and hear well; and the wings of the bat are so exceedingly sensitive that it will move about blindfolded and with ears stopped with cotton almost as unerringly as when aided by sight and sound. Insects have smell, sight, and taste well developed, as is shown by their keen appreciation of the colours, perfumes, and flavours of flowers. They also hear. Stridulation proves this. Worms have eyes and ears, and land-leeches scent the approach of their prey at a long distance. The starfish and the medusa respond to all the five classes of stimuli which affect the five senses of man, and nervous substance is found in all animals above the sponge.
Memory is the power of retaining or recognising past states of consciousness. The power to retain impressions follows in origin close upon the power to receive impressions. Memory is the historic faculty of the mind—the power of the mind to store up its experiences—and is found in nearly all animals. The lowly limpet, whose world is a seaside rock, will come back from its little roamings time after time to the same rude lodge from which it set out. Bees remember where they get honey or sugar months afterwards, and when it is necessary will sometimes go back to the old home hive which they left the year before. Ants retrace their steps after making long journeys from their nest, and are able in some way to recognise their friends after months of separation. The stickleback (fish) knows the way back to his nest, although he has been absent several hours. Fishes return and hatch their young year after year in the same waters; birds come back to their old nesting-places; and horses remember their way along devious roads over which they have not been for years. Horses used in the delivery of milk, or in other occupations in which they are accustomed to travel daily over about the same route, come in time to remember every alley, street, and stopping-place of the whole round almost as accurately as their drivers. Darwin’s dog remembered and obeyed him after an absence of five years. The power of dogs, squirrels, and other animals of remembering where they have long before cached food is indeed wonderful. A squirrel will come down out of a tree when the earth is covered to a depth of several inches with lately fallen snow and hop away, without the slightest hesitancy or mistake, to the exact spot where it has months before stored its mid-winter acorns. A lion has been known to recognise its keeper after seven years of separation, and an elephant obeyed all his old words of command on being recaptured after fifteen years of jungle life. The similarity of memory in other animals to the same faculty in man is shown by the fact that memory everywhere is governed by the same laws. In all animals, including man, memory is strengthened by repetition—that is, impressions are always deepened and confirmed by being made over and over. A parrot or a raven masters a new sentence by working at it and saying it over and over again, just as a boy memorises his rules and catechisms.
Imagination is the picturing power of the mind. In its lowest stages of manifestation it is akin to memory. Imagination, however, in its higher reaches, not only reimages previous impressions, but combines them in new and original relations. Imagination is displayed in dreams, images, delusions, anticipation, and sympathy. It also furnishes wings for speculation and reason. Spiders, when they attach stones to their webs to steady them during anticipated gales, probably exercise imagination. The tame serpent which was carried away from its master’s house and found its way back again, though the distance was one hundred miles, no doubt carried in its imagination vivid pictures of its old home.[1a] Cats, dogs, horses, and other animals dream, and parrots talk in their sleep. Horses and cattle sometimes stampede at imaginary objects, and often distort real objects into imaginary monsters. When a horse at night takes fright at a big black stump by the roadside, he no doubt imagines it to be some terrible creature ready to eat him up if he should go near it, just as a timid child does in the same circumstances. There is a great difference in horses in this respect, just as there is among children and men, some of them taking fright at every unusual thing, while others are more bold or stolid. The cat playing with a ball of yarn converts it by means of its imagination into an object of prey, just as a girl converts a doll into a baby, or a boy changes a stick into a steed. Sympathy is the putting or picturing of one’s self in the place of another, and by means of the imagination sharing or simulating the psychic conditions of that other. This high and holy exercise of the imagination is exhibited by horses, cattle, dogs, deer, elephants, monkeys, and birds—in fact, by nearly all animals as far down as the fishes and insects.
Emotion is the stirring of the sensibilities by way of the intellect or the imagination. The following emotions are found in non-human beings: fear, surprise, affection, pugnacity, play, pride, anger, jealousy, curiosity, sympathy, emulation, resentment, appreciation of the beautiful, grief, hate, cruelty, joy, benevolence, revenge, shame, remorse, and appreciation of the ludicrous. Excepting the emotions of conscience and religion, which are really compounds, with fear as the main ingredient, this list of non-human emotions is coextensive with the list of human emotions. Many of these emotions germinate low down in the animal kingdom, fear, anger, sexuality, and jealousy all being found in fishes and in the higher invertebrates. In the higher vertebrates many of these emotions are almost as strong as they are in men. Does anyone who has felt the throbbing sides of a frightened puppy or hare have any doubt that these creatures suffer the keenest agony of fear? Apes have been known to fall down and faint when suddenly confronted by a snake, so great is their instinctive horror of serpents; and gray parrots, which are extremely nervous birds, have been known to drop from their perch unconscious under the influence of great fear.[2]
The horse is, perhaps, of all animals, the one which occasionally gives itself over most completely to the emotion of fear, as everyone who has witnessed the terrible abandon of a runaway team can testify. Ants, fishes, birds, cats, dogs, horses, monkeys, porpoises, and many other animals play. Young kittens, colts, and puppies enjoy a scuffle about as well as boys do. Pugnacity originates among the spiders and insects, and is highly developed in the ant, cock, and bulldog. This emotion is strong in the males of nearly all vertebrates. Anyone who has observed the vigilance displayed by fishes in protecting their nests can have little doubt that these comparatively primitive beings possess pugnacity. I was one evening floating in a boat by the edge of a Long Island pond just over a village of perches. Each nest was guarded by an assiduous male, who hovered over it vigilantly, or darted this way and that to drive off the piscatorial hoi polloi hanging about the neighbourhood, ready to slip in at the first opportunity and eat the eggs. Just to see what would happen, I put my hand down into the water and moved it slowly toward one of the nests. To my surprise, the guardian of the nest, instead of fleeing in alarm, proceeded to show fight. It chased my hand away time after time, and when the hand was not removed it would nip it vigorously, not once simply, but two or three times if necessary, and each time with increasing energy. It contended with the courage of a little hero. I pushed it and jostled it about, and even took it in my hand and lifted it clear out of the water. To my amazement, on getting back into the water, it returned promptly to the attack. It fought until it was really fagged, for its onsets were at last much feebler than at first. I came away after twenty minutes, leaving the little hero in triumphant possession of his charge.
Among some species of monkeys several individuals will join together in overturning a stone for the possible ants’ eggs under it; and, when a burying beetle has found a dead mouse or bird, it goes and gets its companions to help it in the interment.[3a] Crows show benevolence by feeding their blind and helpless companions, and monkeys adopt the orphans of deceased members of their tribe. Brehm saw two crows feeding in a hollow tree a third crow which was wounded. They had evidently been doing this for some time, for the wound was several weeks old. Darwin tells of a blind pelican which was fed upon fishes, which were brought to it by its friends from a distance of thirty miles.[4a] The devotion of cedar-birds to each other and their kindness to all birds in distress are well known to every student of ornithology. Olive Thorne Miller tells of a cedar-bird that raised a brood of young robins that had been left orphans by the accidental killing of the parents. Weddell saw more than once during his journey to Bolivia that when a herd of vicunas were closely pursued the strong males covered the retreat of the weaker and less swift members of the herd by lagging behind and protecting them.[3b]
A remarkable instance of altruism which he once saw exhibited by the king-crabs in a London aquarium is mentioned by Kropotkin in his work on ‘Mutual Aid a Factor in Evolution.’ One of these crabs had fallen on its back in a corner of the tank. And for one of these great creatures, with its saucepan carapace, to get on its back is, even in favourable circumstances, a serious matter. The seriousness was increased in this instance by an iron bar, which hindered the normal activities of the unfortunate crustacean. ‘Its comrades came to the rescue, and for one hour’s time I watched how they endeavoured to help their fellow-prisoner. They came two at once, pushed their friend from beneath, and after strenuous efforts succeeded in lifting it upright. But then the iron bar prevented them from achieving the work of rescue, and the crab again fell heavily on its back. After many attempts, one of the helpers went into the depth of the tank and brought two other crabs, who began with fresh forces the same pushing and lifting of their helpless comrade. We stayed in the aquarium for more than two hours, and, when leaving, came to cast a glance upon the tank. The work of attempted rescue still continued. Since I saw that I cannot refuse credit to the observation quoted by Dr. Erasmus Darwin that the common crab during the moulting season stations a sentinel, an unmolted or hard-shelled individual, to prevent marine enemies from injuring moulted individuals in their unprotected state.’ Walruses go to the defence of a wounded comrade when summoned by its cries for help. Romanes tells of a gander who acted as a guardian to his blind consort, taking her neck gently in his mouth and leading her to the water when she wanted to take a swim, and after allowing her to cruise for a time under his guidance and care, conducting her back home again in the same thoughtful manner. When goslings were hatched, this remarkable gander seemed to realise the inability of the mother to look after them, for he took charge of them as if they were his own, convoying them to the waterside, and lifting them carefully out of the ruts and pits with his bill whenever they got into difficulty.[1b]
The disposition to go to the aid of a fellow in trouble is one of the most characteristic traits in the psychology of the swine. A single squeal of distress from even the scrawniest member of a swine herd will bring down on the one who causes this distress the hair-raising wrath of every porker within hearing. This trait has been considerably reduced by domestication, and in those varieties in which degeneracy has gone farthest it scarcely exists. But it is exceedingly strong in all wild hogs. Animals as low in the scale of development and as proverbially cold as snakes have been known, when educated and treated with kindness, to manifest considerable affection for their friends and masters. Nearly all domestic animals display a good deal of affection, not only to their young, but to adult members of their own kind and to their human masters. The devotion of the dog to man is without a parallel anywhere. It has been said that ‘the dog is the only thing on this earth that loves you more than he loves himself.’ When dogs become so much attached to their masters or mistresses that they pine and die on being separated from them, they show beyond any question that they have feelings which, in intensity, are not inferior to those possessed by the more highly developed men and women. And this has happened time after time.
A pathetic story of love and of its tragic close came last year out of the Maine woods. Two moose, who had been tracked all day by a couple of human tigers, were finally overtaken, when one of them fell pierced by two rifle-balls. The remaining moose, instead of dashing off into the forest, stood still, lowered its head, and sniffed at its fallen companion. Then, raising its antlers high into the air, it bellowed loudly. As the cry of the great creature echoed through the forest, it also fell at the discharge of the rifles. It was found on examination afterwards that the first moose was blind, and that the second one, which had neglected to leave it for safety, was its pilot.
My father once owned a cow who contracted a strong affection for my sister. This cow, who showed on many occasions and in many ways her highly developed emotional nature, would scarcely allow anyone else than my sister to milk her. She always presented herself to my sister as soon as she was let into the lot in order to be milked first, and she was so jealous of this privilege that if it were not accorded to her she would stand with her head down and give vent to her unhappiness in low moans. After she was milked she would follow her human friend around from one cow to another, in order to be as near her as possible. She knew my sister’s voice from that of everyone else, and would always low a response and come to her when called by name, even though she were a quarter of a mile away in the pasture. Romanes tells somewhere of a band of apes that were being pursued by dogs when a young ape was cut off from the rest and was about to be killed by the dogs. The chief of the band, seeing the peril of the young one, went deliberately back and rescued it.