COSMIC PHILOSOPHY 



maintain an equilibrium between organisms and 

 their environments ; 



6. But the environment of every group of 

 organisms is steadily, though slowly, changing ; 



7. Every group of organisms must accord- 

 ingly change in average character, under penalty 

 of extinction ; 



8. Changes due to individual variation are 

 complicated by the law that a change set up in 

 any one part of a highly complex and coherent 

 aggregate, like an organism, initiates changes in 

 other parts ; 



9. They are further complicated by the law 

 that structures are nourished in proportion to 

 their use ; 



10. From the foregoing nine propositions, 

 each one of which is indisputably true, it is an 

 inevitable corollary that changes thus set up and 

 complicated must eventually alter the specific 

 character of any given group of organisms ; 



11. It is postulated that, since the first ap- 

 pearance of life upon the earth's surface, suffi- 

 cient time has elapsed to have enabled such 

 causes as the foregoing to produce all the spe- 

 cific heterogeneity now witnessed. 



It seems to me that this summary fairly re- 

 presents the logical character of the theory of 

 natural selection. The theory is so strong that 

 no scientific writer is disposed to deny that the 

 process of natural selection has always gone on 

 68 



