376 Evolution and Adaptation 



or even injurious to a slight degree, it might have been 

 retained, as appears in fact to be the case in the change of 

 color of the green lizards. 



Increase of Organs through Use and Decrease 

 through Disuse 



We meet here with one of the most characteristic and 

 unique features of living things as contrasted with non-living 

 things. We shall have to dismiss at once the idea that we 

 can explain this attribute of organisms by either the selec- 

 tion or the mutation theory ; for we find animals possessing 

 this power that could never be supposed to have acquired it 

 by any experience to which they have been subjected ; and 

 since it appears to be so universally present, we cannot 

 account for it as a chance mutation that may have appeared 

 in each species. No doubt Wolff had responses of this kind 

 in view when he made the rather sweeping statement that 

 purposeful adaptation is the most characteristic feature of 

 living things. The statement appears to contain a large 

 amount of truth, if confined to the present group of phe- 

 nomena. 



This power of self-regulation may confer a great benefit 

 on its possessor. The increase in the size and strength of 

 the muscles through use may give the animal just those 

 qualities that make its existence easier. The increase in the 

 power of vision, or at least of visual discrimination through 

 use, of the power of smell and of taste, of hearing and of 

 touch, are familiar examples of this phenomenon. 



However much we may be tempted to speculate as to how 

 this property of the animal may have been acquired, we lack 

 the evidence which would justify us in formulating even a 

 working hypothesis. It may be that when we come to know 

 more of what the process of contraction of the muscle in- 

 volves, the possibility of its development as a consequence 



