126 THE NEW PHYSIOLOGY. 



do, the only answer is that it is part of the nature of 

 reality that they do so. It is only from actual observa- 

 tion of them that we can predict their behaviour ; and 

 to predict we must make use, not of the conception of 

 " things," and their definite and limited " properties," 

 but of the distinctive conception, based on actual obser- 

 vation, of life. The ideal conceptions of the physical 

 sciences are good enough tools for many practical pur- 

 poses, but not for grappling with the phenomena of life. 



Darwin emphasised the fact of variation, but without 

 pointing out its characteristic feature as adaptation. 

 To my mind this is a serious defect in his argument. 

 Organisms struggle, not for any sort of existence, but 

 for their own specific sort of existence ; and in whatever 

 direction heritable variation may occur, and whether 

 it be in the direction of further development or of de- 

 generation, the variation has the distinctive character 

 of adaptation. In Mendelian variations, no less than 

 in other variations, organic wholeness and continuity 

 express themselves clearly. In the structural and 

 functional abnormalities or variations resulting from 

 the accidents of the reproductive process, this wholeness 

 and continuity are just as evident as in the case of 

 injuries or diseases which have been recovered from. 



From the point of view of pure biology, the struggle 

 for existence is a blind struggle. But in so far as organ- 

 isms are conscious this is no longer the case, and the 

 Darwinian theory does not apply. Adaptation is no 

 longer blind. I do not, however, propose to discuss in 

 this lecture the significance for evolution of psychical 

 facts. 



The prevailing popular physiology of Darwin's time 



