PHILOSOPHICAL CONCLUSIONS. 379 



at all the decision that the sun, while it is the cause when we 

 speak of the development of the leaf, is not the cause when 

 we speak of the particular course of that development. 



When we seek the cause of the changing of the characters 

 of organisms in the course of geological history the same 

 reasoning applies. 



The fact that an infinitesimal part of the differences in the 

 characters of organisms is an expression of adaptation to the 

 immediate conditions of its local and temporal environment 

 does not suffice to prove that the environment is the cause of 

 the adjustment. 



The determination of the true relations of cause and 

 effect in nature is therefore not a matter of observation, but 

 interpretation of cause is founded upon the philosophy we 

 apply in the interpretation of the course of nature. 



Ability to Adjust the Organization to Conditions of Environ- 

 ment a Chief Element in the Fitness for Survival. It is un- 

 doubtedly true that the fittest do survive, but too much is 

 made of the theory that fitness consists in precision of adjust- 

 ment of organic structure to conditions of environment. If 

 this were true the less variable would be more fit than the 

 more variable, and the result of survival would be the cessa- 

 tion of variation; whereas it is probably much nearer the 

 truth to say that fitness to survive is in almost direct propor- 

 tion to the ability to vary. 



Darwin did not find it essential to inquire why variation 

 takes place: variation was assumed to be a common fact in 

 the life of organisms, and it is one of the chief factors of 

 evolution. But when we push the question, why has a par- 

 ticular variation arisen, become abundant, and been trans- 

 mitted from generation to generation? we are forced to 

 the conviction that the primal characteristic which distin- 

 guishes it from its unsurviving fellows is its greater capacity 

 to modify its structure, function, and habits into fitness for 

 the particular conditions of environment. It is the greater 

 ability to adjust, not the closer adjustment of structure to 

 environment, which constitutes the higher fitness to survive. 

 An organism is the fittest to survive, not because it has less 

 to oppose it, or less to overcome, not because the condi- 



