FORMATION OF HABITS IN THE TURTLE. 519 



THE FORMATION OF HABITS IN THE TURTLE.* 



By ROBERT MEARNS YERKES, 



HARVARD UNIVERSITY. 



TZTABITS are determinants in human life. It is true that 

 -1 — *- we are f ree ^ 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 sub- 

 sequent activities and constitute the physical basis of habit. Repe- 

 tition 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 swim- 

 ming is not an instinctive act; he has to learn every detail of the com- 

 plex muscular process by trial; he has to establish by repetition of the 



* 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. 



