HEREDITY OF SAVAGENESS AND WILDNESS 289 



Tests of savageness, wildness, and timidity were made with 

 eight male and eighteen female tame rats (some wide, some 

 narrow). Each individual was tested twice, the tests being 

 separated by an interval of one month. In no case did the 

 males receive a grade above o. All were so gentle and tame 

 that they could readily be taken up in the ungloved hand and 

 examined. The females were decidedly less gentle and tame 

 than the males. Two of the eighteen tested received a grade 

 of i for savageness and fourteen of the eighteen received a 

 grade of i for wildness. The number receiving a grade above 

 o for timidity was twelve. 



The contrast between the wild and the tame rats with respect 

 to savageness, wildness, and timidity is extremely marked. 



The first generation of hybrids was obtained in almost all 

 cases by crossing a wild male with a tame female. This mating 

 is much more satisfactory, because more likely to yield off- 

 spring, than the mating of a wild female with a tame male. By 

 crossing the first generation hybrids among themselves, without 

 selection with respect to savageness, wildness, and timidity, the 

 second generation hybrids were obtained. Up to the present, 

 no third generation hybrids have been examined. 



As the mating, numbering, and weaning of the rats used 

 were attended to by Professor Castle and Doctor Phillips, the 

 experimenter was wholly unprejudiced, while making his tests, 

 by knowledge of the genetic relations of the individuals. Very 

 rarely indeed did he know whether the individual under obser- 

 vation was a tame rat or a first or second generation hybrid 

 rat. Thus, he was able to escape entirely the influence of pos- 

 sible presuppositions concerning the behavior of savageness, 

 wildness, and timidity in heredity. 



With a few exceptions, each individual was tested from three 

 to five times, at intervals of several days. The first test was 

 made, as a rule, at the age of about six weeks and the remain- 

 ing tests usually covered a period of at least a month, some- 

 times two months. It was noted that in general the animals 

 receive lower grades with repetitions of the tests. This is due 

 in part to the experience of being handled, but even more to 

 the fact that they become accustomed to seeing human beings 

 and to being disturbed when fed or when the cages are cleaned. 

 There is also some evidence that ageing has something to do 

 with the change. 



