34 Problems of Organic Adaptation 



It has sometimes been said that while racial adaptations 

 are due to natural selection, individual adaptations are due 

 to the "plasticity" of the organism; but this is merely seek- 

 ing refuge in a name. Plasticity is only passivity and is no 

 explanation at all. It has also been suggested that individual 

 adaptations are problems of development rather than of 

 evolution, of physiology rather than of phylogeny. But 

 this distinction also is nominal rather than real, for evolu- 

 tion is only one form of development, and phylogeny no less 

 than ontogeny must be based on physiological processes. It 

 is true that individual adaptations are things with which 

 we can deal directly by experimental .methods, whereas 

 racial adaptations were established in the more or less dis- 

 tant past and are not readily submitted to experimental 

 tests. Therefore we ought to know more about the causes 

 of individual adaptations than of racial ones, but hitherto 

 attention has been focussed largely upon the latter and rela- 

 tively little study has been given to the former. One of the 

 greatest needs of biology is for more detailed and accurate 

 information regarding individual adaptations; we must 

 know exactly what happens in each case the physiology 

 of the response irrespective of its usefulness and then per- 

 haps the latter may find an explanation. 



Many of these physiological processes are in a certain 

 balance with one another or with the environment, and when 

 this balance is disturbed there is a compensatory regulation. 

 For example, a muscle that is neither increasing nor decreas- 

 ing in size receives a certain amount of blood; increased use 

 of this muscle is balanced by an increased flow of blood, 

 and decreased use leads to a decrease in the blood supply; 

 correspondingly, the muscle increases or decreases in size. 

 Similarly, if one kidney is removed the one that remains has 

 to perform the functions of two, and it receives more blood 



