(3) Adaptations to external conditions. 



(4) Functional adaptations. 



With regard to mutilations there is no trustworthy 

 evidence that such are heritable. ^ It is difficult, more- 

 over, to believe that the modifications made on our bodies 

 by accidents, by disease, by exposure to environment, or by 

 the functional activity of parts, for such are occurring every- 

 day, are heritable. Brown-Sequard 's experiments on 

 guinea pigs, in which he produced epilepsy by the section of 

 certain large nerves and epileptic symptoms appeared in 

 the offspring of a few of the animals, have been frequently 

 quoted in proof of the transmissibility of acquired charac- 

 ters. Later investigators, however, failed to confirm 

 Brown-Sequard 's experiments; besides, his results are 

 capable of another interpretation (Consult Thomson's 

 Heredity). 



Some experiments have been conducted in transplant- 

 ing plants and animals to a new environment, when marked 

 changes of habit occurred. But here again no conclusions 

 of a definite nature can be drawn. 



In the discussion of this subject the real question at 

 issue is: Does a structural change of this kind in a part of 

 the body so influence the germ plasm that the offspring will 

 show the same modification? No one doubts that environ- 

 mental influences may have an indirect influence on the off- 

 spring, but this is not to the point. 



It must be confessed that much of the discussion as to 

 the heritability of acquired characters has arisen through a 

 misunderstanding of the exact nature of acquired characters 

 and in applying loose methods of reasoning. ^ Thomson 

 ably summarizes these and similar misunderstandings after 

 the following manner: 



1. Interpretations are not necessarily facts. — Many facts 

 of nature, such as the disappearance of the legs of snakes, 

 the hardening of the hoofs, the long neck of the giraffe, etc., 

 are explained as due to the action of use and disuse, but 

 these interpretations may be erroneous. 



2. Begging the question. — It is often assumed that cer- 

 tain characters such as short-sightedness and rheumatism 

 are modifications, and transmissible. But may these not 

 be congenital characters ? 



(1) — For example, the riglvt of circumcision and the docking of lambs' 

 tails have been practised for hundreds of generations. 



(2) — Lamarckians object to the practice of Weismannists of calling 

 acquired characters congenital as soon as they are shown to be 

 heritable. 



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