Page:Popular Science Monthly Volume 58.djvu/527

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FORMATION OF HABITS IN THE TURTLE.

THE FORMATION OF HABITS IN THE TURTLE.[1]
By ROBERT MEARNS YERKES,

HARVARD UNIVERSITY.

HABITS are determinants in human life. It is true that we are free, within limits, to form them; it is also true that, once formed, they mold our lives. In the life of the brute habit plays an even more important role than it does in man. The ability to survive, for example, frequently depends upon the readiness with which new feeding habits can be formed. So, too, in case of dangers habitually avoided, those individuals which form habits most quickly have the best chances of life. But it is unnecessary to emphasize the importance of habit to all living beings, for it is obvious. We have now to ask, What precisely is a habit?

A habit proves in analysis to be nothing more or less than a tendency toward a certain action or line of conduct—a tendency due to structural and functional modifications of the organism which have resulted from repetition of the action itself; for nothing can be done by the animal mechanism without resultant changes in its organization. These changes it is which influence all subsequent activities and constitute the physical basis of habit. Repetition of an act apparently leads to the formation of a track for the controlling nervous impulse—a line of least resistance, so to speak—along which the current therefore tends to pass. A duck when thrown into the water does not have to stop to think what to do to get out, how to move this leg and then that; it instinctively, we say, meets the situation with that combination of movements called swimming. But the duck swims almost, if not quite, as well the first time it is put into the water as it ever does. There is little profiting by experience. This simply means that the structural basis of the swimming habit is present at birth, and does not have to be formed by repetition of the action thereafter. The habit is, in other words, inherited. For man swimming is not an instinctive act; he has to learn every detail of the complex muscular process by trial; he has to establish by repetition of the


  1. This article is based upon an experimental study of the associative processes of turtles made at the Marine Biological Laboratory, Woods Holl, Mass., during the summer of 1899, under the direction of Dr. E. L. Thorndike. My thanks are due Dr. Thorndike and Prof. C. O. Whitman, the director of the laboratory, for their kindness.