XVI ARE ACQUIRED CHARACTERS INHERITED ? 341 



the environment, are mere individual effects which are 

 not hereditary ; while, whenever such changes appear in 

 species that have long been subjected to uniform conditions 

 — as in the case of the Texan Saturnia — they indicate 

 that some portion of the external peculiarities of those 

 species were individually acquired characters, and there- 

 fore afford strong evidence of the non -inheritance of such 

 characters. 



Summary of the Argument. 



I have now fairly met, so far as the space at my 

 disposal will allow, the strongest arguments of the 

 advocates of use-inheritance as a law of nature and as a 

 factor in evolution. I have shown that the effects which 

 it ought to produce in the case of mankind do not appear, 

 and that breeders of animals do not recognise it as a factor 

 to be taken account of. The alleged cases of inherited 

 habits or instinct, supposed to be useless, are shown in one 

 case to be not necessarily so ; while all such cases involve 

 so many elements of uncertainty or ignorance that no 

 conclusion of value can be drawn from them. The alleged 

 difficulty of the origin of horns except by the inherited 

 effect of blows and pressures, I have shown to be founded 

 on error as to fact ; and their origin by normal variation 

 and their development where useful by selection, to be 

 supported by the frequent occurrence of dermal excres- 

 cences in many animals. The case of the mammalian 

 teeth has been shown to be quite explicable without use- 

 inheritance, the mode of action of which is, in this case, 

 itself inexplicable. Mr. Herbert Spencer's three main 

 arguments to prove the inadequacy of natural selection have 

 been fully discussed, and have, I venture to think, been 

 shown to be entirely inconclusive, since they are either 

 founded on comparatively unimportant and adventitious 

 peculiarities, or on a neglect of some of the most important 

 conditions under which natural selection in its various 

 forms comes into play. 



In order to render the position clearer I wish, before 

 concluding, to say a few words on the general question. 



