ATAVISM. 145 



as well. The importance of this fact can hardly 

 be overstated. If it were more generally under- 

 stood that physical and mental derangements that Family Traits 

 have obtained in a family one, two or three gen- ^PP 63 ** 

 erations back, even though absent in the present 

 generation, are likely to reappear in the next, those 

 contemplating marriage and parentage would cer- 

 tainly use discretion in the selection of the com- 

 panion. 



The causes of atavism have never been fully 

 determined. My own thought is that use and dis- 

 use and heredity are the principal ones. In the 

 evolution and development of all physical and 

 mental attributes use or exercise is the all-potent Causes of 

 factor. Change of environments, habits and con- Atavism. 

 ditions in life produce new requirements that in 

 turn develop new functions and characters ; func- 

 tions and characters thus acquired become fixed 

 in the species or family fixed only in the sense 

 that they represent the established order of life. 

 With change of environment or condition the es- 

 tablished order of life changes and functions pecu- 

 liar to the old environment drop into disuse and 

 finally become latent. In this latent state the Y 

 are not manifest in the life or character of the 

 species or family, but are transmitted, generation 

 after generation, as a part of the fixed pattern of 

 life, gradually becoming weaker and weaker until 

 finally they may become extinct altogether. If, 

 however, before the latent function or character 

 becomes extinct there are conditions or exciting 

 causes calculated to stimulate it, the ancestral 

 trait may become manifest. Thus a morbid con- 

 dition, such as insanity, kleptomania, cruelty or 



