Popular Science Monthly/Volume 68/March 1906/Trial and Error as a Factor in Evolution


By Professor W. B. PILLSBURY,


SINCE Darwin wrote there have been many general formulæ advanced under which all forms of development might be brought, and while each has sufficed for a time, each has been seen to fail and each has been replaced with greater or less completeness when tested by a new set of facts. While no one of the formulae can be regarded as final, each has been valuable in so far as it has summarized the facts and points of view of the age under which it has developed.

Within the last decade there seem to be facts developing in varying fields that support a new formula, which, while perhaps not so definite in its explanation as many that have preceded it, can at least lay claim to very wide application. This generally stated is that all progress is the result of chance trials and a selection from the trials of those that are successful in attaining some end. The first formulation of the process in so many words seems to have been to describe the method by which animals learn. As Professor Thorndike and many later investigators have shown, an animal learns simply as the result of a selection from his chance movements—those which serve for some definite end. When a horse learns to open a gate or a dog to bring a stick through a fence, learning is accomplished by trying all possibilities until the end desirable at the moment is attained, and after it is once attained there is usually a smaller number of false movements and a shorter time of accomplishment at each succeeding trial, until finally all movements but the right one have been eliminated. These observations make a sufficient number of possible movements and a selecting agent the only essentials in the learning process.

From this comparatively modest starting point the doctrine has extended in both directions. It seems fairly evident from experiments that man must learn new movements in exactly the same way as the animal. He, too, can not be helped to learn by being put through the movement from outside. Knowledge of anatomical relations and rational external knowledge is valueless except as it serves as a point of departure. The only method by which the child or man can acquire new movements is by painfully trying and selecting the movements that most nearly accomplish the end in view.

Recently Professors Jennings and Holmes, in studies of the reactions of relatively low forms of life, seem to show that much that has hitherto been regarded as an almost machine-like response to external stimulation is not made with the definiteness that has been supposed. On the contrary, what seems to take place is a feeling about for a favorable condition. When this is found there is either continued motion in this most favored direction or quiescence in the most favorable position. Here again we should have to do with trial and error, but with less complicated possibility of movement and, in all probability, with a different basis for the selection of the favorable condition.

Still a fourth expansion of the category of trial and error is possible in a metaphorical sense. This is to explain the general course of evolution. If we accept in all strictness the conclusions of Weismann, there is no possibility of foreseeing with very great accuracy any change in a race. Changes of one kind appear here, changes of another kind appear there. Aside from the conditions of mating, however, there is no way of tracing to any known causes the changes observed. We are left then with what, at the present stage of knowledge, seem entirely unforeseen and undetermined chance changes in the animal structure, with an accompanying set of instincts and general activities. The real determining factor is, of course, natural selection. In brief the environment determines which of the many forms and functions that originate by chance shall survive. By personification, and even more literally, we can think of the chance variations as the analogue of the trials of the individual animal, and survival as corresponding to the movement that is successful and so retained.

If we should then be permitted to generalize, we should have chance at the basis of all learning, all advancement, all adaptation. The primary facts would be the variation in structure, which would form the basis for all other adaptation. Within the organism at the lowest stage would be found adaptation from moment to moment on the basis of successful chance adjustment. At this stage, however, there is no learning. One adjustment is of no value for later activities, as the animal is at the same level, in the same condition, after the adaptive movement has been made as it was before. At the next stage, in addition to the increased complexity of the organism which makes possible more numerous movements, there is retention of the successful trials. A movement once made is accompanied by a change in the organism which makes that movement more likely to occur in the future. From this point upward there is variation in degree of complexity of possible movements, in the readiness with which movements once attained are retained and repeated, but there is no great change in the mechanics of the problem.

What does change throughout, and what is, after all, on this theory the essential factor in all development, is the selecting agent and the rewards which serve to make one thing permanent rather than another. The selecting agent in the race is the environment, and the agent of selection is always life and death. If the organism varies in a way that is suitable, it lives and its progeny multiply. If, on the contrary, some variation be unfavorable, death is its punishment, the animal is eliminated, and nothing further is heard of it in the struggle for existence.

In the earliest forms, in the paramecium, upon which Professor Jennings has worked, or in the blow-fly larva, that Professor Holmes investigated, we can hardly imagine that there is much more than vague chemical activity or quiescence. When the light is favorable, motion directly ahead is preferred, or no motion at all. The animal moves away rather than towards the light when negatively phototactic merely because there is no physico-chemical tendency to draw back the head when it is turned away from the light and there is a stimulus which leads to general locomotion. We have to do with the rudiments of pleasure and pain, perhaps, but we can be sure of nothing more than increased tendency toward motion in one position and decreased tendency to movement in the other. It is approximately a mechanical equivalent of pleasure and pain.

At the next level of complexity in animal learning, the case is not so different. The simplest answer to the question is that the creature is controlled by pleasure and pain. It is not as clear as might be imagined at first sight what this means in last analysis, for, at the very lowest, pain and pleasure must go for their ultimate explanation to the evolution of the species. Other factors are perhaps to be found in the earlier experience of the animal and in even more remote circumstances. While we can not unravel the tangle of factors involved in what we call pleasure and pain, yet it may be interesting to indicate that, regarded as a selecting agent, neither is a simple thing but the result of many factors. It is at least worth while to indicate that the deciding factors here are conscious, as opposed to the chemical or physical processes in the organism or to the natural forces in the environment. There may be nothing really new or peculiar in the circumstances or conditions, but it does mean that we classify the manifestations under a new head. This alone makes it worth while to set the selecting agent off as belonging to a special class or group.

If we bring the different groups under a single general statement, we should have racial progress, due to the chance variations in the animal structures, and have as the selecting agent the environment, which enforces its decrees through the life or death of the organism, or, at least through its nourishing or its failure to flourish. The adaptation of the individual would take place in the lower forms through chance responses to stimulation, which were in the main not determined by the nature of the stimulus, but which attained their end by a selection in terms of the chemical constitution of the organism. Each adaptation here is without influence upon later reactions, but each must be hit upon anew each time the circumstances arise. There is no learning. At the next stage again the response is brought about by chance, and the selection determines the process in its completeness, but there is here, on the one hand, a conscious pleasure and pain, and what is more certain and more important as an objective criterion, there is a permanent effect left upon the organism by the action once performed.

In man and perhaps in some of the higher animals the same general processes hold, but in addition to immediate organic processes of pleasure and pain there are new elements added to the selecting agencies, which may ultimately become pleasure and pain, but are only remotely organic in their origin. These in some way all seem to originate in the social milieu, all seem to have their origin in the phenomena connected with the living of man in groups. There are many things which seem indifferent to racial survival or to immediate pleasure and pain that will always and at once be repressed in terms of good manners or good form. Some traditional virtues strike one who has been reared in a given society as just as fundamental as others which can be shown to possess survival values, but we find civilizations of high rank which survive just as well without them. So, if an Anglo-Saxon were to select the fundamental virtues, modesty would be one of them. But let him consider for a moment the customs of the Japanese, and their national success, and then modesty would not seem so fundamental as it did at first sight.

These more subtle selecting agents act in the same way as the cruder. When any individual by chance departs from the traditional line of conduct, he is at times made to feel by popular attitude that he himself or his conduct is not welcome. It is not merely departure from the social norm that is repressed, but departure in certain ways that can not be foretold in advance of trial. Some innovations are welcomed and accepted and the discoverer made a social hero, exceptional man or genius. Others are checked in one or more of the insidious ways that in society are more effective than the arm of law. What determines this social selection, however, is not evident. In extremes it may be racial survival, in minor cases it may be what passes for esthetic appreciation, although esthetic appreciation can probably be reduced to social selection as well as social selection to esthetic appreciation.

One thing seems fairly evident, and this is that imitation does not play the important part in social selection or in any form of learning that has been supposed. In these higher forms, what we want explained is not the persistence of the traditional conduct, but the determining factors in selecting some and eliminating other departures from the traditional methods of action. Even in the learning: of children or of animals, the striking feature of the process is not the fact that the child gradually approaches the standard of society, but the method by which the approach is brought about. If you study a child learning to speak, it will at once be seen that there is no inherent impulse to repeat the sounds that are spoken, but that all sorts of movements are made, and those which in themselves are interesting or acquire vicarious interest from their resemblance to the sounds about are repeated until learned. The child does not imitate everything, although from the indifference of his interests he sometimes seems to. His imitation is not from a desire to reach an end; rather the child selects from the spontaneous unforeseen movements of all kinds those which strike his fancy. In spite of the fact, then, that there seems to be no instinct in the German child to speak German rather than English, he nevertheless selects from his varying movements those which resemble the sounds that he hears and so he learns to speak German. The sounds heard about him are by no means the incentive to the endeavor. Experiments seem to indicate that even in adults a knowledge of what it expected, or even a desire to execute a certain movement when one has exact anatomical knowledge of the parts to be moved, is no aid to its accomplishment in advance of trial. Much less then can we assume that the unappreciated presence of a sound can spur to its production by the child. The instincts that may serve to produce the sounds from which selection is made are varied and are the expression of numerous connecting paths in the nervous system. There is no evidence of an instinct or impulse to imitate for the sake of imitation.

The explanation of the numerous actions that are imitated by the child is to be found, on the one hand, in the great variety of useless movements at his command, and on the other in the wide range of his interests as yet unrestricted by the training that tends to restrain the adult individual in one relatively narrow line.

Imitation, then, seems to be a subordinate form of the general law of learning rather than learning a subordinate form of imitation. The explanation of learning that depends upon trial and error alone differs from an explanation in terms of imitation merely in that it makes individual appreciation of the results of a movement the essential element rather than the presence of a similar movement in some of the individual's neighbors. The two theories are alike in that the former must insist that seeing a fellow perform the movement is an important factor in raising individual appreciation. But they must differ in that it as firmly denies that seeing a movement performed is any incentive to its performance by the second individual. A movemerit seen may become interesting if the organism chances to throw out a similar movement immediately after the first has been observed, but it will serve merely to make the individual repeat it a second time when once it has been made by chance; it will not serve to initiate a movement of itself.

The social factors which have been brought under the general term imitation have much the same relation to the more complicated conduct of the affairs of life that the simple copy has in spurring to the more simple and immediate action. They do not primarily initiate but serve to select factors otherwise initiated. Good form may lead to conscious imitation in an adult who already has command over the movement. Fashion may directly bring about imitation in the matters of dress, where the movements are already under control and mental processes alone are involved in the choice, but the impelling forces in society are those that make a man shunned who offends, and give him renewed applause when he initiates valuable lines of action. The enforcement of the moral law, apart from the material agencies, depends not upon precept or good example, but upon these vague social forces that are constantly repressing some and rewarding other departures from the accepted standards. Some of those rejected are rationally and by association apparently no worse than those retained. But social selection is none the less definite and absolute in fact because it seems irrational when attempt is made to explain it theoretically. The man who departs from the traditional course takes his reputation in his hands, for society is essentially conservative. Chances are that the result will be social death, and reasonably so, because the long course of evolution would probably make the existing the best, when we are dealing with any course of conduct that can have any survival value. Were it possible to reduce all the influences of social control to immediate or traditional survival values, the problem would be very much simpler than is really the case. Many courses of action which society represses most rigidly are apparently indifferent to survival, and many can not easily be shown to be associated with lines of action that could have been of value at present or at any earlier period.

The nature of the action selected will vary from civilization to civilization and from people to people and even from community to community within the same civilization. It does not seem possible as yet to push very far in the analysis of these elements, but it is nevertheless valuable to recognize their importance for both individual and sociological psychology. An insistence upon the importance of this factor under the term imitation or what else has probably been the most important contribution that psychological sociology has made, and an analysis into its elements and tracing it back to causes would undoubtedly have even more important results.

Looking back upon our general summary of this modern formulation of development as a whole we may ask what its value may be. The chief importance lies in the fact that it permits one to bring the generally accepted facts of racial and individual development under a single phrase. Even though the words are used in a slightly different sense, it is evident that chance gives the variations upon which all development must be based, even though the factors that we must assume to bring about the chance result are not altogether the same in the racial as in the individual development. The process of selection is also much the same throughout, for selection results from mere survival of one and rejection of others.

The main lack in the formula is our inability at present to analyze or define all the selecting agents. The environment in general which serves as the agent in racial development is comparatively well understood, or at least the meaning of the word and the methods of producing results give definite pictures. On the other hand, the physico-chemical constitution of the organism which must be assumed in the lowest organisms, and the intimate nature of social pressure which is effective in man both need much more complete analysis. And even pleasure and pain are not as simple or as free from ambiguity as we are inclined to suppose at first sight. But at least each of them marks a fairly definite field for investigation and will serve in so far to satisfy the needs of a formulation of the facts already known, and act as a spur to further work.