5280 THE THEORIES OF EVOLUTION 



The theory of organic selection endeavours, like 

 Weismann's theory of germinal selection, to dispose 

 of grave objections made by the anti-selectionists, by 

 compromising with them on several points, and to a 

 certain extent, it attains its purpose. All the theories 

 based solely on innate variations or on acquired modi- 

 fications are weakened by their exclusiveness. The 

 theory of organic selection, which recognises the in- 

 fluence of those two factors, is more inclusive and 

 nearer the truth. It gives at least an explanation of 

 the fact of common observation that, when a group 

 of individuals is submitted to the influence of a new 

 environment, they do not all respond in the same de- 

 gree to the new stimulus. For example, if the fur 

 of several black animals transported to the polar re- 

 gions turns white, the degree of discolouration will 

 not be the same in every animal; the peculiar sensi- 

 tiveness to a change in climate evinced by some of 

 them is certainly due to a germinal peculiarity. 



Unfortunately, this theory does not solve the prob- 

 lem in a satisfactory way; like all the theories which 

 j)ostulate the cumulation of innate variations, it fails 

 to supply a physiological explanation of that cumula- 

 tion. Furthermore, even if we accept the "illusory" 

 heredity of acquired characters as a satisfactory ex- 

 planation of useful adaptations, we cannot very well 

 understand the transmission of peculiarities which 

 lack usefulness, such as the colouration of butterflies, 



