LOGICAL POSITION OF THE ARGUMENT 239 



when natural selection ceases to affect its degree of development — 

 " would be incredible, even were the assumptions of the theory 

 valid." But as a sequence of disuse the change is clearly explained. 

 Prof. Lloyd Morgan replies : "Is there any evidence that a structure 

 really dwindles through disuse in the course of individual life ? Let 

 us be sure of this before we accept the argument that vestigial organs 

 afford evidence that this supposed dwindling is inherited. The 

 assertion may be hazarded that, in the individual life, what the evi- 

 dence shows is that, without due use, an organ does not reach its full 

 functional or structural development. If this be so the question 

 follows : How is the mere absence of full development in the indi- 

 vidual converted through heredity into a positive dwindhng of the 

 organ in question ? " Moreover, the convinced Neo-Darwinian is 

 not in the least prepared to abandon the theory of dwindling in the 

 course of panmixia, especially in the light which Weismann's con- 

 ception of germinal selection has thrown on this process. 



§ 13. The Logical Position of the Argument 



Before we state what appears to us at present the inevitable 

 conclusion, it may be useful to indicate briefly the logical position 

 of the argument. 



Weismann has pointed out that there are two possible methods 

 by which the affirmative position — that modifications are trans- 

 missible — might be established. In the first place, there might 

 be actual experimental proof of such transmission ; in the second 

 place, there might be a collection of facts which cannot be in- 

 terpreted without the hypothesis of modification-inheritance. 



Experiment. — The experimental method has not been followed 

 as often as might have been expected, and where it has been 

 followed the results are far from conclusive. But it is important 

 to remember that although a few good cases of the inheritance 

 of an acquired character would prove the possibility of such in- 

 heritance, hundreds of failures to demonstrate the transmission 

 experimentally do not prove that it is impossible. 



The Neo-Lamarckian believes that when new conditions of life 



