CHAPTER XXIII 
ARE ACQUIRED CHARACTERS (MODIFICATIONS) 
HEREDITARY ? 
Inrropucrory Nore.—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. ARTHUR 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 (1) 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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