Introduction to the Science of Sociology

by Robert Ezra Park; E. W. Burgess

The widespread interest in the study of children has inspired in recent years a considerable literature bearing upon the original and inherited tendencies of human nature. The difficulty of distinguishing between what is original and what is acquired among the forms of behavior reported upon, and the further difficulty of obtaining accurate descriptions of the situations to which the behavior described was a response, has made much of this literature of doubtful value for scientific purposes. These studies have, nevertheless, contributed to a radical change in our conceptions of human nature. They have shown that the distinction between the mind of man and that of the lower animals is not so wide nor so profound as was once supposed. They have emphasized the fact that human nature rests on animal nature, and the transition from one to the other, in spite of the contrast in their separate achievements, has been made by imperceptible gradations. In the same way they have revealed, beneath differences in culture and individual achievement, the outlines of a pervasive and relatively unchanging human nature in which all races and individuals have a common share.

The study of human nature begins with description, but it goes on from that point to explanation. If the descriptions which we have thus far had of human nature are imperfect and lacking in precision, it is equally true that the explanations thus far invented have, on the whole, been inadequate. One reason for this has been the difficulty of the task. The mechanisms which control human behavior are, as might be expected, tremendously complicated, and the problem of analyzing them into their elementary forms and reducing their varied manifestations to precise and lucid formulas is both intricate and perplexing.

The foundation for the explanation of human nature has been laid, however, by the studies of behavior in animals and the comparative study of the physiology of the nervous system. Progress has been made, on the one hand, by seeking for the precise psycho-chemical process involved in the nervous reactions, and on the other, by reducing all higher mental processes to elementary forms represented by the tropisms and reflex actions.

In this, science has made a considerable advance upon common sense in its interpretations of human behavior, but has introduced no new principle; it has simply made its statements more detailed and exact. For example, common sense has observed that "the burnt child shuns the fire," that "the moth seeks the flame." These are both statements of truths of undoubted generality. In order to give them the validity of scientific truth, however, we need to know what there is in the nature of the processes involved that makes it inevitable that the child should shun the fire and the moth should seek the flame. It is not sufficient to say that the action in one case is instinctive and in the other intelligent, unless we are able to give precise and definite meanings to those terms; unless, in short, we are able to point out the precise mechanisms through which these reactions are carried out. The following illustration from Loeb's volume on the comparative physiology of the brain will illustrate the distinction between the common sense and the more precise scientific explanation of the behavior in man and the lower animals.

It is a well-known fact that if an ant be removed from a nest and afterward put back it will not be attacked, while almost invariably an ant belonging to another nest will be attacked. It has been customary to use the words memory, enmity, friendship, in describing this fact. Now Bethe made the following experiment: an ant was placed in the liquids (blood and lymph) squeezed out from the bodies of nest companions and was then put back into its nest; it was not attacked. It was then put in the juice taken from the inmates of a "hostile" nest and was at once attacked and killed. Bethe was able to prove by special experiments that these reactions of ants are not learned by experience, but are inherited. The "knowing" of "friend and foe" among ants is thus reduced to different reactions, depending upon the nature of the chemical stimulus and in no way depending upon memory.

Here, again, there is no essential difference between the common sense and the scientific explanation of the behavior of the ant except so far as the scientific explanation is more accurate, defining the precise mechanisms by which the recognition of "friend and foe" is effected, and the limitations to which it is subject.

Another result of the study of the comparative behavior of man and the lower animals has been to convince students that there is no fundamental difference between what was formerly called intelligent and instinctive behavior; that they may rather be reduced, as has been said, to the elementary form of reaction represented by the simple reflex in animals and the tropism in plants. Thus Loeb says:

A prominent psychologist has maintained that reflexes are to be considered as the mechanical effects of acts of volition of past generations. The ganglion-cell seems the only place where such mechanical effects could be stored up. It has therefore been considered the most essential element of the reflex mechanism, the nerve-fibers being regarded, and probably correctly, merely as conductors.

Both the authors who emphasize the purposefulness of the reflex act, and those who see in it only a physical process, have invariably looked upon the ganglion-cell as the principal bearer of the structures for the complex co-ordinated movements in reflex action.

I should have been as little inclined as any other physiologist to doubt the correctness of this conception had not the establishment of the identity of the reactions of animals and plants to light proved the untenability of this view and at the same time offered a different conception of reflexes. The flight of the moth into the flame is a typical reflex process. The light stimulates the peripheral sense organs, the stimulus passes to the central nervous system, and from there to the muscles of the wings, and the moth is caused to fly into the flame. This reflex process agrees in every point with the heliotropic effects of light on plant organs. Since plants possess no nerves, this identity of animal with plant heliotropism can offer but one inference—these heliotropic effects must depend upon conditions which are common to both animals and plants.