344 THE EVOLUTION THEORY 



I should here mention all who have shared in the achievement by 

 observation or reflection. Whoever has helped it on even a single 

 step may say to himself that he has taken an active part in bringing 

 about what must be called essential progress in human knowledge. 



But in the. science of nature every new solution implies the 

 cropping up of a new riddle, and we are immediately confronted with 

 the problem, Why should nature, in the course of evolution, have 

 interpolated this process of the mingling of different hereditary sub- 

 stances almost everywhere in the organic world ? This, however, is 

 a problem which we cannot attack until we have first made our- 

 selves more fully acquainted with the phenomena of inheritance, and 

 have attempted to reason back from these to the nature of the 

 hereditary substance. We must, in short, think out a theory of 

 heredity. 



