MATURATION AND USE IN THE DEVELOPMENT 

 OF AN INSTINCT 



J. F. SHEPARD AND F. S. BREED 

 From the Psychological Laboratory, University of Michigan 



Two figures 



INTRODUCTION 



The work reported in this paper was done in the Psychological 

 Laboratory of the University of Michigan during June, July and 

 August, 1 91 2. The problem grew in a very natural way out of 

 a previous study 1 of the pecking instinct in barred Plymouth 

 Rock chicks. In this earlier work a method was devised whereby 

 the course of development in accuracy of the pecking reaction 

 was satisfactorily traced. After the developmental curve of the 

 instinct had been found, the question arose as to how much of 

 the improvement from day to day is attributable to practice 

 and how much is due to maturation apart from practice. To 

 quote from an earlier article : 



" One sometimes speaks of the modifiability of an instinctive 

 action like that of pecking, but wherever this term has been 

 employed in this paper in connection with instinct no more 

 has been mplied than the objective fact of improvement in 

 accuracy, an increasingly successful adjustment of parts in a 

 more comprehensive function. The problem still remains, Is 

 this development dependent upon practice, or is it the natural 

 functional correlate of structural maturation independent of 

 practice? Swallows are reported to be able to fly without pre- 

 vious practice. If the pecking of chicks could be successfully 

 inhibited for a week's time without doing violence to the normal 

 physical condition of the animals, would the accuracy of the 

 reactions at the end of that time average 36.67 on a scale of 

 50, the average for our lot of twenty-one? There is evidence 

 in support of the belief that such chicks would very quickly be 

 pecking with average efficiency, without anything like the 



1 F. S. Breed. The development of certain instincts and habits in chicks. Be- 

 havior Monographs, 1911, vol. 1, no. 1, p. 14 ff. 



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