THE HEREDITY OF SAVAGENESS AND WILDNESS 



IN RATS 



ROBERT M. YERKES 

 Harvard University 



In 1 910 Professor William E. Castle suggested to me the 

 desirability of studying the heritability of savageness and wild- 

 ness in certain strains of rats which were being bred for studies 

 in the heredity of structural characteristics at the Bussey Insti- 

 tution. I undertook the proposed investigation, and by the 

 generous aid of Professor Castle and Doctor John C. Phillips 

 I have been enabled to test the behavior of nearly three hundred 

 individuals. The investigation is incomplete, and in this paper 

 I propose to present merely a preliminary report, reserving the 

 detailed account of my work, with the experimental data, for 

 a paper to be published later, in some journal of genetics. 



At the outset I made a preliminary analysis of the behavior 

 of some of the rats in order to discover several traits which 

 seemed to be fairly isolable and capable of reasonably accurate 

 measurement. As a result of these observations, I decided to 

 make tests of the savageness, wildness, and timidity of wild 

 rats, tame rats, and of the first and second generation hybrids. 



Preliminary attempts at measurement indicated that six 

 grades, with respect to these several traits, might be utilized. 

 These grades I designated as o, 1, 2, 3, 4, and 5. The grade 

 o indicates the absence of the various signs of savageness, wild- 

 ness, or timidity. The grade 5 indicates the presence of these 

 signs in maximal number and intensity. 



In order to obtain a rough measure of the reliability of my 

 judgments, I tested the individuals of several litters of rats 

 with respect to the three traits designated and, later, without 

 knowledge of my previous results, retested the same individ- 

 uals. A comparison of the measurements thus obtained indi- 

 cated that they were often the same and seldom differed by 

 more than a grade. The results given below are typical. 



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