440 DARWINISM 



The Non-Heredity of Acquired Characters. 



Certain observations on the embryology of the lower 

 animals are held to afford direct proof of this theory of heredity, 

 but they are too technical to be made clear to ordinary 

 readers. A logical result of the theory is the impossibility of 

 the transmission of acquired characters, since the molecular 

 structure of the germ-plasm is already determined within the 

 embryo ; and Weismann holds that there are no facts which 

 really prove that acquired characters can be inherited, although 

 their inheritance has, by most writers, been considered so prob- 

 able as hardly to stand in need of direct proof. 



We have already shown, in the earlier part of this chapter, 

 that many instances of change, imputed to the inheritance of 

 acquired variations, are really cases of selection ; while the very 

 fact that use implies usefulness renders it almost impossible to 

 eliminate the action of selection in a state of nature. As 

 regards mutilations, it is generally admitted that they are not 

 hereditary, and there is ample evidence on this point. When 

 it was the fashion to dock horses' tails, it was not found that 

 horses were born with short tails ; nor are Chinese women 

 born with distorted feet ; nor are any of the numerous forms 

 of racial mutilation in man, which have in some cases been 

 carried on for hundreds of generations, inherited. Neverthe- 

 less, a few cases of apparent inheritance of mutilations have 

 been recorded, 1 and these, if trustworthy, are difficulties in the 

 way of the theory. The undoubted inheritance of disease is 

 hardly a difficulty, because the predisposition to disease is a 

 congenital, not an acquired character, and as such would be the 

 subject of inheritance. The often-quoted case of a disease 

 induced by mutilation being inherited (Brown-Sequard's 

 epileptic guinea-pigs) has been discussed by Professor Weis- 

 mann, and shown to be not conclusive. The mutilation itself 

 — a section of certain nerves — was never inherited, but 



new forms. Again, in parthenogenetic females the complete apparatus for 

 fertilisation remains unreduced ; but if these varied as do sexually produced 

 animals, the organs referred to, being unused, would become rudimentary. 



Even more important is the significance of the " polar bodies," as explained 

 by Weismann in one of his Essays ; since, if his interpretation of them be 

 correct, variability is a necessary consequence of sexual generation. 



1 Darwin's Animals and Plants, vol. ii. pp. 23, 24. 



