But this element of consciousness is one which it is exceedingly difficult to detect in our analysis, and yet upon it our classification and the psychic position of an animal must to a great extent depend. The amœba contracts when pricked, jelly-fishes swim toward the light, the earthworm, "alarmed" by the tread of your foot, withdraws into its hole. Are these and similar actions reflex or instinctive? A grain of consciousness preceding an action which before has been reflex changes it into instinct. Mr. Romanes, probably correctly, regards them as purely reflex. We must, I think, believe that these actions result in consciousness even in the lowest forms. The selection and attainment of food certainly looks like conscious action. Probably all nerve-cells or nervous material were originally, even in the lowest forms, dimly conscious; then by division of labor some became purely conductive, others more highly perceptive. The important thing for us to remember in our present ignorance is not to be dogmatic.
Furthermore, the gain of a grain of consciousness of the adaptation of certain means to special ends changes instinctive action into intelligent, and its loss may reverse the process. Fortunately we have found that in so far as actions, even instinctive, are modified by experience, they are becoming to that extent intelligent. This criterion of intelligence seems easily applied. But this profiting by experience must manifest itself within the lifetime of the individual, or in lines outside of circumstances to which its ordinary instincts are adapted, or we may give to individual intelligence the credit due really to natural selection. We must be cautious in our judgments.
These reflex actions are performed independently of consciousness or will. Consciousness may, probably does, attend the selection and grasping of food; but most of the actions of the body will go on better without its interference. It is not yet sufficiently developed, or, so to speak, wise enough to be intrusted with much control of the animal.
Among higher worms cases of instinct seem proven. Traces of it will almost certainly be yet found much lower down. Fresh-water mussels migrate into deeper water at the approach of cold weather. And if the clam has instincts, there is no reason why the turbellaria should not also possess them. But all higher powers develop gradually, and their beginnings usually elude our search. Along the line leading from annelids to insects instinct is becoming dominant. A supraœsophageal ganglion has developed, and has been relieved of most of the direct control of the muscles. Very good sense-organs are also present. From this time on consciousness becomes clearer, and the brain is beginning to assert its right to at least know what is going on in the body, and to have something to say about it. Still, as long as the actions remain purely instinctive the brain, while conscious, is governed by heredity. The animal does as its ancestors always have. It does not occur to it to ask why it should do thus or otherwise, or whether other means would be better fitted to the end in view. It acts exactly like most of the members of our great political and theological parties. And until the animal has a better brain this is its best course and is favored by natural selection.
But the hand of even the best dead ancestors cannot always be allowed to hold the helm. The brain is still enlarging, the sense-organs bring in fuller and more definite reports of a wider environment. Greater freedom of action by means of a stronger locomotive system is bringing continually new and varied experiences. And if, as in vertebrates, longer life be added, frequent repetition of the experience deepens the impression. Slowly, as if tentatively, the animal begins to modify some of its instincts, at first only in slight details, or to adopt new lines of action not included in its old instincts, but suited to the new emergencies. This is the dawn of intelligence. Its beginnings still remain undiscovered. Mr. Darwin believes that traces of it can be found in earthworms and other annelids. He also tells us that oysters taken from a depth never uncovered by the sea, and transported inland, open their shells, lose the contained water, and die; but that left in reservoirs, where they are occasionally left uncovered for a short time, they learn to keep their shells shut, and live for a much longer time when removed from the water. If oysters can learn by experience, lower worms probably can do the same.
Certain experiments made on sea-anemones, actinæ animals a little more highly organized than hydra, demand repetition under careful observation.[5] The observer placed on one of the tentacles of a sea-anemone a bit of paper which had been dipped in beef-juice. It was seized and carried to the mouth and here discarded. This tentacle after one or two experiments refused to have anything more to do with it. But other tentacles could be successively cheated. The nerve-cells governing each tentacle appear to have been able to learn by experience, but each group in the diffuse nervous system had to learn separately. The dawn of this much of intelligence far down in the animal kingdom would not be surprising, for the selection and grasping of food has always involved higher mental power than most of the actions of these lowest animals. Memory goes far down in the animal kingdom. Perhaps, as Professor Haeckel has urged, it is an ultimate mental property of protoplasm. And the memory of past experience would continually tend to modify habit or instinct.
It is unsafe, therefore, to say just where intelligence begins. At a certain point we find dim traces of it; below that we have failed to find them. But that they will not be found, we dare not affirm. In the highest insects instinct predominates, but marks of intelligence are fairly abundant. Ants and wasps modify their habits to suit emergencies which instinct alone could hardly cope with. Bees learn to use grafting wax instead of propolis to stop the chinks in their hives, and soon cease to store up honey in a warm climate.
Our knowledge of vertebrate psychology is not yet sufficient to give a history of the struggle for supremacy between instinct and intelligence, between inherited tendency and the consciousness of the individual. But the outcome is evident; intelligence prevails, instinct wanes. The actions of the young may be purely instinctive; it is better that they should be. But instinct in the adult is more and more modified by intelligence gained by experience. There is perhaps no more characteristic instinct than the habit of nest-building in birds. And yet there are numerous instances where the structure and position of nests have been completely changed to suit new circumstances. And the view that this habit is a pure instinct, unmodified by intelligence, has been disproved by Mr. Wallace. But while size of brain, keenness of sense-organs, and length of life may be rightly emphasized as the most important elements in the development of vertebrate intelligence, the importance of the appendages should never be forgotten. Cats seem to have acquired certain accomplishments—opening doors, ringing door-bells, etc.—never attained by the more intelligent dog, mainly because of the greater mobility and better powers of grasping of the forepaws. The elephant has its trunk and the ape its hand. The power of handling and the increased size of the brain aided each other in a common advance.
The teachableness of mammals is also a sign of high intelligence. The young are often taught by the parent, a dim foreshadowing of the human family relation. And we notice this capacity in domestic animals because of its practical value to man. And here, too, we notice the difference between individuals, which fails in instinct. All spiders of the same species build and hunt alike, although differences caused by the moulding influence of intelligence will probably be here discovered. But among individual dogs and horses we find all degrees of intelligence from absolute stupidity to high intelligence. And many mammals are slandered grievously by man. The pig is not stupid, far from it.
Still only in man does intelligence reign supreme and clearly show its innate powers. But even in man certain realms, like those of the internal organs, are rarely invaded by consciousness, but are normally left to the control of reflex action. These actions go on better without the interference of consciousness.