Popular Science Monthly/Volume 58/March 1901/The Formation of Habits in the Turtle
|THE FORMATION OF HABITS IN THE TURTLE.|
By ROBERT MEARNS YERKES,
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 activity the basis of the habit. Finally, however, the man will be able to meet the situation—water, a distant shore, and a desire to be on the shore—as the duck does—that is, habitually.
Since habits make an animal what it is in great part, the study of their formation, of the manner and rapidity of their growth, and of their permanence must be of practical as well as of scientific importance. We are rapidly realizing, as the increasing interest in animal psychology clearly indicates, that the mental life of all animal types must be understood before we can attain to a satisfactory science of psychology or give a history of the evolution of mind. To watch the progress of a habit's growth is exceedingly interesting, whether the subject be a man or one of the lower animals. Ordinarily the chief difficulties in the way of such a study are the great length of time and the constancy of observation necessary. But these obstacles may readily be avoided by making observations under artificial or experimental conditions—that is, by adapting conditions to the needs of the experiment, instead of trying to adapt one's self to natural conditions. The account which follows presents, as an example of this kind of work, observations on habit formation in the common 'speckled turtle' (Chelopus gutiaius). It has been my aim to give a brief account of the way in which a particular turtle profited by experience.
The work was undertaken to determine to what extent and with what rapidity turtles can learn; to measure as accurately as might be their intelligence. Reptiles are usually considered sluggish and unintelligent creatures, and there can be no question about the general truth of this opinion. Turtles certainly appear to be very stupid—so much so, indeed, that one would not expect much in the way of intelligent actions. Just how stupid, or better perhaps, just how intelligent they are, we shall be better able to judge after studying the habits of the animals more carefully, and collecting more evidence like the following:
The finding of the way through a labyrinth to a nest was chosen as the habit to be studied. The motives employed to get the subject to try to find its way to the nest were: first, the desire to hide in some dark, secluded place; secondly, the impulse to escape from confinement; and lastly, the desire to get to a place of comfort. Dr. Thorndike, in studying the associative processes of cats and dogs (of which a brief account appeared in the Popular Science Monthly for August, 1899), used hunger as the chief motive for escape. This is unsatisfactory in the case of turtles, because they frequently do not eat well in confinement, and at best their feeding or desire for food is very irregular and hard to control as a motive in experimental work.
The method of experimentation was simple. A box three feet long, two feet wide and ten inches deep was divided into four portions by partitions, also ten inches deep, arranged as shown in Fig. 1. In each partition was a hole four inches long and two inches deep, just large enough to permit the turtle to pass through easily. The box is shown in ground plan by Fig. 1.
A is the space in which the animal was placed to start, the starting-point being marked by a dot (.). The corner marked nest contained a mass of damp grass and was darkened. When everything was ready for an experiment the animal was placed in A at the dot and allowed to wander about until it found the nest by passing through the openings marked 1, 2 and 3.
On July 20 the animal, a speckled turtle about four inches long which was found in Woods Holl, Mass., was placed in A for
|Fig. 1. Plan of Labyrinth No. 1.||Fig. 2. Course for Fourth Trip.|
the first time. After wandering about almost constantly for thirty-five minutes, it chanced to find the nest, into which it immediately crawled, there remaining until taken out for another experiment two hours later. The observations were made from one to two hours apart, in order to avoid fatiguing the animal, and also to leave it some inducement for seeking the nest, for if it were taken out each time as soon as it got back to the comfortable corner, the game would soon lose interest. The second time the nest was reached in fifteen minutes, with much less wandering. The time for the third trip was five minutes, and for the fourth, three minutes thirty seconds. During the first three trials the courses taken were so tortuous that it seemed foolish to try to record them. There was aimless wandering from point to point within each space, and from space to space. After the third trip the routes became much more direct, and accurate records of them were obtained. Fig. 2 gives the course taken in the fourth experiment. It is fairly direct, but shows that the animal lost its way in A and again in B; having passed through 2, it took the shortest path to the nest.
A record of the route in connection with the time of the trip is necessary as an index of the effect of experience, because if the animal takes a direct course, with no wrong turns, but makes several halts, the time may indicate no profiting by the former acts, whereas the route will at once show that there has been improvement. Thus one record supplements the other.
These experiments were made six or eight times a day until fifty trials had been given. The tenth trip was made in three minutes five seconds, with two mistakes in turning. The time of the twentieth journey was but forty-five seconds, and that of the thirtieth, forty seconds. In the latter experiment a direct course was taken; this was also true in the case of the fiftieth trip, which was made in thirty-five seconds. Fig. 3 represents graphically the times of the first twenty experiments of this series. The vertical
|Fig. 3. Times of Experiments from One to Twenty.||Fig. 4. Plan of Labyrinth No. 2.|
column of figures at the left, 1 to 40, indicates minutes; the horizontal line of figures, 1 to 20, gives the number of trials.
That the turtle profited by experience, and that very rapidly, is evident from the figures. The average time for the first ten trips, from one to ten, was eight minutes fifty-four and a half seconds; the average time of the ten trips between thirty and forty was one minute three seconds. What at first took minutes, after a few trials required only as many seconds. There was remarkably little aimless wandering, crawling up the sides of the box and sulking in the corners after the third experiment. In fact, the animal soon began to behave as if it had the goal in mind and was intent on making directly for it. It learned with surprising quickness to make the proper turns and to take the shortest path. Three or four times I noticed it turn in the wrong direction, crawl into a corner and, as it seemed, become confused, for it then returned to the starting-point, as if to get its bearings, and started out afresh. In every case the second attempt resulted in a direct and unusually quick journey to the nest. Very frequently halts just in front of the holes were noticed. It looked as if the animal were meditating upon the course to be taken. Had one seen a man in a similar situation he would unhesitatingly have said that the person was trying to decide which way to go. There can be little doubt, however, that the mental attitude of the turtle was extremely simple compared with a man's under similar conditions. There are those who would claim that even the turtle was thinking about its environmental conditions, but it seems far more probable that it stopped in order the better to get those sensory data by which it was enabled to follow its former course. Smell and sight furnish the most important elements in the associative processes of lower animals. This interpretation of the action is supported
|Fig. 5. Course for Fifth Trip.||Fig. 6. Course for Thirtieth Trip.|
by the fact that it occurred most frequently after the course had been gone over a few times.
A more complex and novel labyrinth was now substituted. Its new features were a blind alley (see F, Fig. 4) and three inclined planes (3, 4 and 6 of Fig. 4). A plan of the labyrinth is shown in Fig. 4. At the left of the nest a side view of the inclines 3 and 4 is shown. Each was one foot long, and the middle point (M) was four inches from the floor.
Labyrinth No. 2 was used in the same way as No. 1, the turtle being placed in A and permitted to seek the nest, which was this time a box filled with moist sand. The inclines at first baffled the little fellow, and it was an hour and thirty-one minutes before he reached the nest. A and B seemed to offer no difficulties, but the new features—the blind alley and the inclines—were puzzles. By the fifth trial, however, these had become somewhat familiar. The route taken in this experiment has been produced in Fig. 5.
The time of this trip was sixteen minutes. The times of some of the other trials were as follows:
The route for the thirtieth trip was, as Fig. 6 indicates, almost direct.
The times of these experiments are generally longer than those of the first series because the inclines consumed considerable time.
During the formation of the habit of crawling up incline 3 and sliding down incline 4 a very interesting modification of the action occurred, namely, the shortening of the path to the sand-box by crawling over the edge of incline 4. At first the animal, after climbing up 3, would slide all the way to the bottom of 4 and would then turn toward the nest. Soon, however, it began making the turn toward the nest before reaching the bottom, thus throwing itself over the edge of 4. The turn was made earlier and earlier on 4, until finally it got to crawling over as soon as it reached the top of 3, or M. It always turned itself over the edge carefully, and landed, after a fall of four inches, usually on its head or back. By this process the path was shortened eight or ten inches. This action is a splendid illustration of the way in which an advantageous habit may grow by accretion, as it were, until it seems as if it must have been the result of reasoning. Some would, no doubt, hold that in this case the turtle chose the direct path because of inferences from judgments. Although this may be true, there is surely a sufficient explanation of the habit, as we have come to know it, in the profiting by chance experience. No one would say that the nest was at first found by inferences. It was reached because of the animal's impulse to move about, to seek escape or hiding. Had the turtle stopped to judge and draw inferences as to the way to escape, instead of persistently moving from place to place, it would probably be in the pen yet. No; the wandering impulse led by chance to the finding of satisfaction, turtle pleasure, in the nest. Because of this satisfaction, the action was impressed on the vital mechanism, so that there was a tendency (the beginning of a habit) toward repetition of it. Had the action failed to give satisfaction, the probability of its being repeated would have been merely that of chance, and not chance plus the influence of the former pleasure-giving activity. The turtle happened to crawl over the edge of the incline, and, finding that this enabled it to get to the nest quicker, it continued the act, thus forming a habit.
Such experiments as these give clear pictures of habit formation in animals. They also furnish a means of measuring with considerable accuracy the rapidity of the process, the degree of intelligence and the permanence of associations, thus making possible a comparison of the mental abilities of different animals.
- 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.
- 'Animal Intelligence, an Experimental Study.'