226 COOK 



* 



To find that organisms differ in different environments is, 

 after all, only to find that they exist, for where the conditions 

 of existence differ the organisms must differ. The power of 

 organisms to form adjustments is a measure of their ability to 

 exist, for no environments are absolutely constant. Species 

 strive, as it were, by every artifice at their command to enlarge 

 their environments, to conquer more opportunities of existence. 

 Now and then a successful combination is attained. 



Causes which can bring characters of selective value into 

 existence can bring other characters as well, and can carry for- 

 ward their development. It is no longer necessary to suppose 

 that natural selection is an evolutionary cause at all, in the strict 

 sense of the word. Selection may still be recognized as a con- 

 dition or an influence in evolution, but there is nothing to show 

 that evolutionary progress is actuated by selection. Fitness, in 

 last analysis, comes by evolution, not evolution by fitness. 

 Selection helps to explain adaptation, but it does not explain 

 evolution ; it enables us to understand why evolution follows 

 some courses and not others, but it does not show how the evo- 

 lutionary advance is accomplished, nor how a new character can 

 develop to the point of utility or harmfulness, so that selection 

 can encourage or restrict it. 



The Lamarckian and the Darwinian theories ascribed evolu- 

 tion to causes resident in the environment. The kinetic theory 

 ascribes it to causes resident in the species. The causes of 

 evolution are not to be ascertained by the solution of the prob- 

 lem of fitness, but lie rather in the constitution of species and 

 in the methods of organic descent. 



2. INTRASPECIFIC DIFFERENCES AS MATERIALS OF EVOLUTION. 



The time has gone by when it was supposed that new knowl- 

 edge could be gained by the analysis and rearrangement of old 

 data and deductions. Nevertheless, it remains true that every 

 advance in science requires, sooner or later, a new and consistent 

 arrangement of the materials of investigation, and of the lan- 

 guage to be used in describing them. Words are not things, 

 but they often control the predisposition of the mind and thus 

 obscure or illuminate the field of mental vision. 



