EVOLUTION 379 



of these modes a change in a living form cannot be 

 permanently established. 



But beyond these methods of transmission we have to 

 see how a change in living forms can be effected. With- 

 out at present defining how change is to be measured we 

 can realise that changes in the aggregate of any form 

 may be produced by (i) modifications of the individual 

 members not due to growth or age ; (2) modifications due 

 to the death of some individuals or to the relatively greater 

 fertility of others. In the first case an acquired, in the 

 second a congenital character is used for the modification 

 of the type. These two modes of change, acquired 

 inodificatioti and selectioji, must transmit their effects 

 either by inheritance or tradition. We have thus four 

 processes for the establishment of change, any one of 

 which may be used to describe the evolution of organic 

 forms. Whether all are really effective can only be 

 determined by quantitative investigation. The inheritance 

 of acquired modifications was accepted without proof by 

 Erasmus Darwin and Lamarck ; it has been warmly 

 advocated by Herbert Spencer, and as warmly repudiated 

 by Weismann and others. Satisfactory numerical demon- 

 stration of its existence is yet wanting. 



The tradition of acquired modifications is clearly 

 a factor of evolution in man, it is largely the means of 

 differentiating civilised from uncivilised man ; habits of 

 life, language, institutions, mechanical and other knowledge 

 serve to distinguish one race from a second. They react 

 upon the environment, upon food supply and relative 

 fertility. They may thus well be sources of progressive 

 change, for it is impossible to consider any form of life 

 merely from its material side, its habits and experience are 

 all really " characters " just as much as the physical shape 

 of its cranium. But clearly if through any change of 

 environment the tradition be destroyed, then we may have 



for his father, and being asked why he was the father, replied at once : 

 "Because he strokes his eyebrow." Thus inquiry was diawn to the point, 

 and the habit's existence in father and sonsaHke confirmed. Are such habits 

 family instincts or traditions? 



