182 DARWINISM TO-DAY. 



Defended." With these, concessions made it is necessary to 

 call to the aid of the selection theory, if it is still to be con- 

 sidered an important factor in species-forming these con- 

 cessions do not, of course, invalidate the claims of selection 

 to be the all-important final factor in determining the 

 general course of evolution, by encouraging or restraining 

 the various general lines of descent certain auxiliary and 

 aiding theories or explanations. Such helps to selection are 

 to be found especially in isolation, organic selection, and 

 the Weismannian theories of panmixia and germinal selec- 

 tion. The outlining of these theories will form the con- 

 tents of our next chapter. 



APPENDIX. 



1 Plate, Ludwig, "Uber die Bedeutung der Darwin'schen Selec- 

 tionsprinzip," 1903. 



2 The question, what is meant by "selective value," has been dis- 

 cussed by Conn ("Method of Evolution," pp. 83-86, 1900), as fol- 



Conn's discus- lo ws : "How useful must a character be to be of 

 sion of selective selective value? Such a question it is, of course, im- 

 valne, possible to answer. The preservation of any particu- 



lar character is not an isolated matter. It is not single characters 

 that are preserved, but a combination of many characters together. 

 The survivor is the animal showing the best combination of char- 

 acters. It may even have some harmful ones, provided the useful 

 ones predominate. The rattle of the rattlesnake has at times doubt- 

 less been of a disadvantage to its possessor, and has caused the 

 death of hundreds of thousands of individuals. It is doubtless 

 possible to show, as Darwin did, that it has also been of value to 

 the animals. But how are we to decide whether its use or dis- 

 advantage is the greater, except by the theoretical conclusion that 

 it must on the whole be useful or it would have been eliminated? 

 The whole study of utility is sure to result in an unsatisfactory 

 circular logic, something as follows : The survival of the fittest is 

 a law. If an organ be not useful it could not have been developed 

 by natural selection. Therefore, all organs and all characters must 

 be useful. Since in such a problem no one can prove a negative, 

 this position cannot be disproved; but it is certainly not very satis- 

 factory. 



