Differences in Behavior 267 



which is expressed by the indices of modifiability 50 and 100. 

 In other words, it took No. 407 twice as long to acquire this 

 habit as it took No. 403. Similarly the ladder-climbing tests 

 revealed important individual differences in ability to profit 

 by experience. In the tables of labyrinth tests (38, 39, 40) 

 individual differences are too numerous to mention. It 

 required forty-nine tests to establish in No. 50 a labyrinth-C 

 habit which was approximately equal in degree of perfection 

 to that which resulted from twenty-two tests in the case of 

 No. 52. The figures in this and other instances do not ex- 

 aggerate the facts, for repeatedly I have tested individuals 

 of the same litter, the same sex, and, so far as I could judge, 

 of the same stage of development, and obtained results which 

 differ as markedly as do those just cited. If space limits 

 permitted, I could present scores of similar differences in 

 docility which the problem, labyrinth, and discrimination 

 methods have revealed. 



In examining the detailed individual results of the various 

 tables for differences of this sort, it is important to bear in 

 mind that sex, age, and descent should be taken into account, 

 for with each of them, as will be shown clearly later in 

 this chapter, sensitiveness, docility, and initiative vary. I 

 have therefore based my statements concerning individual 

 differences in docility upon the results of comparison of mice 

 of the same litter, sex, and age. It is safe to say that human 

 beings similarly selected for comparison do not exhibit greater 

 differences in ability to profit by experience than did these 

 dancing mice. 



The facts concerning individual differences in initiative 

 which I have discovered are not less definite than those of 

 the preceding paragraphs. From the beginning of my study 

 of the dancer I observed that what one individual would 

 readily learn of his own initiative another never learned. For 



