252 COOK 



We permit ourselves to say that agriculture was learned in 

 some such accidental way, but we forbear to say that plants 

 also learn to adapt themselves to take better and better advan- 

 tage of environmental requirements. We base the distinction 

 on the fact that we have reasons for our actions, but in the great 

 majority of comparable cases the reasons have been discovered 

 long after the arts had been perfected. We have theories of 

 swimming, but young children often swim quite as instinctively 

 as animals. 



This may appear an entirely irrelevant digression, but a use- 

 ful purpose may have been served if we are ready to recognize 

 the essential unity of the phenomena of accommodation or direct 

 adaptation and cease to demand special explanatory terms and 

 hypothetical forces for each of the multifarious forms of adap- 

 tive change. The explanation will come when our knowledge 

 of protoplasmic organization has sufficiently increased, but in 

 the meantime we gain nothing by multiplying the mystery or 

 by giving it a multitude of names. 



Under the theory that environment causes evolution a very 

 real and important relation was supposed to exist between 

 artisms, or adaptive alternative characters inside species, and 

 ecology, or the study of the adaptive characters of species. 



Artisms or environmental adjustment variations have received 

 much consideration from those who have held that evolution is 

 caused by the environment, and who have believed, in accord- 

 ance with this view, that the environmental variations were true 

 examples of progressive evolutionary change, carried forward 

 by external influences. 



This doctrine became untenable when Weismann showed that 

 characters directly " acquired" from the environment are not 

 inherited, that is, they do not show any tendency to repeat them- 

 selves unless the inducing conditions are present. Weismann 

 proposed to explain the possession by the same species of alter- 

 native characters by his theory of determinants, or internal 

 " mechanisms of heredity." These determinants were thought 

 to control in advance the characters of the organism, and alter- 

 native characters were explained as the work of two or more 

 sets of determinants which could be brought into action by par- 



