CHAPTER XXXI 



ARE ACQUIRED CHARACTERS (MODIFICATIONS) 



HEREDITARY? 



Introductory Note. — In a previous chapter (chap, xvi), under the heading 

 "Heredity in Pure Lines," it was pointed out that germinal variations are hered- 

 itary, and somatic variations (modifications) are not hereditary. That germinal 

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

 also made clear in the discussion of mutations, 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 1 



J. AKTHUR 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 difficult, and (2) that in the supply of 

 germinal variations, whose transmissibility is unquestioned, there is 

 ample raw material for evolution. We know a little 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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