412 PROGRESS OF SCIENCE IN THE CENTURY. 



Transmissibility of Acquired Characters or Modi- 

 fications. — Since 1883, when Weismann expressed 

 his entire scepticism as to the transmission of ac- 

 quired characters, the question has been almost con- 

 tinuously debated. This is not surprising, for it is 

 much more than a technical problem for biologists. 

 It is of profound interest to the parent, the physi- 

 cian, the teacher, the moralist, and the social reform- 

 er; and it really concerns us all, for the answer to it 

 affects every-day conduct. This is sufficient reason 

 for devoting some attention to it here, and this 

 is further justified by the fact that although the 

 negative position has been tentatively assumed at 

 various periods, e.g., by Kant and by Prichard 

 (b. 1Y86), the careful discussion of the question is 

 characteristic of the last quarter of the nineteenth 

 century, and dates from an essay by Galton in 

 18Y5,* and from one by Weismann in 1883. f 



^^Modifications'' or ^'^ Acquired Characters'' may 

 be defined as structural changes in the body of the 

 organism induced by changes in the environment or 

 in the function, and such that they transcend 

 the limit of organic elasticity, and therefore persist. 

 Plants of the plain when brought into Alpine condi- 

 tions may develop more protective tissue and exhibit 

 many other modifications. The white man who 

 works for many years under a tropical sun may be- 

 come so deeply tanned that the result does not dis- 

 appear after years of residence in Britain. Unlike 

 the Ethiopian he has changed his skin, but he cannot 

 change it back again. Through prolonged disuse 



*A Theory of Heredity, Contemporary Review, XXVIL, 

 pp. 80-95. 



t Uel)er die Yererhung, Jena, trans. Oxford, 1889. 



