HEREDITY OF WILDNESS AND SAVAGENESS IN 



MICE 



INTRODUCTION 



For many years, especially since the appearance of Galton's 

 work on the inheritance of mental abilities (1869), students of 

 heredity have recognized the possibility that mental character- 

 istics are inherited as well as the physical and, perhaps, in a 

 somewhat similar way. The later studies of Galton (1897), 

 and those of Woods (1906), Pearson (1903), Ellis (1904), Bentley 

 (1909), Davenport (1896), Goddard (1911), Conklin (1915), 

 and others tend to substantiate the hypothesis of the inherit- 

 ance of mental traits. 



All of these studies, however, pertain to the heredity of mental 

 or moral characteristics in mankind, and the data from which 

 the studies were made were obtained from various historical 

 and observational sources. In 1910 Professor Robert M. 

 Yerkes began an investigation of the hereditability of savage- 

 ness, wildness, and timidity in rats (1913). So far as the writer 

 has been able to ascertain this was the first study in mental 

 heredity to be made in a laboratory where the conditions under 

 which the subjects lived could be controlled to some extent. 

 The rats used in this study numbered 300 and consisted of 

 wild rats, tame rats, first generation hybrids obtained from 

 crosses of the wild w4th the tame rats, and the second genera- 

 tion hybrids procured by crossing the first generation among 

 themselves. The investigation, though incomplete, proved 

 conclusively that these three characteristics, wildness, savage- 

 ness, and timidity are heritable in rats. 



In order to gain more definite information concerning the 

 modes of transmission' of such behavior-complexes as the above, 

 the writer, at the suggestion of Professor Yerkes, undertook the 

 investigation described in this paper. Owing to the limited 

 space in the Harvard Psychological Laboratory mice were 

 used instead of rats. The study was begun in December, 1911, 

 and continued without interruption until May, 1914. The 



