120 EVOLUTION OF LIVING ORGANISMS. 



Variation is due to change in the metabolism ; all 

 organisms are the products of the interaction of trans- 

 mitted factors of metabolism (the factors of the in- 

 heritance) and factors of the environment. The ever- 

 changing and continuous stream of living matter is 

 diverted into this or that channel of differentiation and 

 specialisation by the environment through natural selec- 

 tion. The environment moulds the organism, and the 

 organism reacts on its environment, until in the case of 

 man he seems to have become master of it and to shape 

 his own destiny, 



