CHAPTER XXIII 



ARE ACQUIRED CHARACTERS (MODIFICATIONS) 



HEREDITARY ? 



Introductory Note. — In the previous chapter, under the heading "Classifica- 

 tion of Variations," the authors pointed out that germinal variations are hereditary, 

 and somatic variations (modifications) are not hereditary. That germinal varia- 

 tions are hereditary and may be produced in a number of different ways was made 

 clear in the last chapter, but the statement that somatic modifications are never 

 in the least hereditary is equivalent to a total denial of the doctrine of the 

 "Inheritance of Acquired Characters," the so-called Lamarckian theory', which was 

 briefly presented in chapter ii. 



This is not a closed question and the final answer has been given neither in 

 the negative nor in the affirmative. The problem is of utmost import for evolu- 

 tionists and for all who are interested in race improvement. So important is it 

 to view this question fairly that we shall quote extensively from several of the 

 leading students of the problem. 



MISUNDERSTANDINGS AS TO THE QUESTION AT ISSUE^ 



J. .\RTHUR THOMSON 



The precise question is this: Can a structural change in the body 

 induced by some change in use or disuse, or by a change in surrounding 

 influence, affect the germ-cells in such a specific or representative way 

 that the offspring will through its inheritance exhibit, even in a slight 

 degree, the modification which the parent acquired ? 



Before we pass to discuss the evidence pro and con it will be useful 

 to notice some frequently recurring misunderstandings, the persistence 

 of which would make further argument futile. 



Misunderstanding I. — How can there be progressive evolution if 

 acquired characters are not transmitted ? — Those who have not thought 

 clearly on the subject often shake their heads sagely and remark that 

 they "do not see how evolution could have been possible at all unless 

 what is acquired by one generation is handed on to the next." To 

 this we have simply to answer (i) that our first business is to find out 

 the facts of the case, careless whether it makes our interpretation of 

 the history of life more or less difhcult, and (2) that in the supply of 

 germinal variations, whose transmissibility is unquestioned, there is 

 ample raw material for evolution. We know a Httle about the abundant 



' From J. A. Thomson, Heredity (copyright 1907). Used by special permis- 

 sion of the publisher, John Murray, London. 



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