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238 THEORETICAL BIOLOGY 



a product of natural forces acting without regard to plan, 

 for the existence of such forces acting in accordance with 

 design was denied. 



As the chance product of the general chaos of Nature, the 

 species and its origin would have become exceedingly un- 

 interesting, were it not that the personal interest which every- 

 one feels in the origin of the species " man " invested this 

 doctrine with immense popularity. 



Darwinism referred everything to matter and the structure 

 of matter, and had no eyes for the living continuity ; then 

 Mendelism came, and swept the whole theory away. 



THE GENOTYPE 



Johannsen is responsible for introducing the distinction 

 between the appearance-type, or phenotype, of an organism, 

 and its rudiment-t5rpe, or genotype. By this means, certain 

 variants were referred to the effects of the environment 

 during genesis, and others to climatic and local influences, 

 while yet others were based on differences in the genes, present 

 from the very beginning. 



Through the method of culture of " pure lines " (i.e. of off- 

 spring from parents having the same genes) and through the 

 culture-experiments made on Paramecium by Jennings, who 

 raised thousands of generations by the division of a single 

 individual of this species of infusorian, it has been proved 

 beyond all question that the genotype of the animal is not 

 subject to any change. The phenotype is exposed to all 

 manner of external influences, whereas the genotype is stable ; 

 this means that the genes present in the germ are inherited 

 unchanged, so long as there is no crossing with other genes. 



It is especially satisfactory that this result should have 

 been reached by Jennings, for he had to depend on it entirely 

 in order to apply to the origin of species his law of " trial 



