THE EVOLUTION OF LIFE 



At the same time I pointed out that in this case two 

 groups of phenomena are closely connected which are 

 often separated — namely, cumulative heredity: firstly 

 external, by the action of the external conditions (food, 

 climate, environment, etc.), and secondly internal, by the 

 reaction of the organism, the influence of internal 

 conditions (habit, use and disuse of organs, etc.). The 

 action of outer influences (light, heat, electricity, press- 

 ure, etc.) not only causes a reaction of the organism 

 affected (energy of movement, sensation, chemosis, etc.), 

 but it has an especial effect as a trophic stimulus on its 

 nutrition and growth. The latter element has been 

 particularly studied by Wilhelm Roux; his functional 

 adaptation (1881) coincides with my cumulative adapta- 

 tion, the close relation of which to correlative adaptation 

 I had pointed out in 1866. Plate has recently given this 

 "definitely directed variation" the name of ectogenetic 

 orthogenesis, or, briefly, ectogenesis. 



The controversy about progressive heredity still con- 

 tinues here and there. Weismann comjjletely denies it, 

 because he cannot bring it into harmony with his germ- 

 plasm theory, and because he thinks there are no experi- 

 mental proofs in support of it. A number of able 

 biologists agree with him, led away by his brilliant 

 argumentation. However, many of them foolishly lay 

 great stress on experiments in heredity which prove 

 nothing; for instance, the fact that the offspring of a 

 mammal that has had its tail cut off do not inherit the 

 feature. A number of recent observations seem to prove 

 that in a few cases even defects of this sort (when they 

 have caused profound and lasting disease of the part 

 affected) may be transmitted to offspring. However, as 

 far as the formation of new species is concerned, the fact 

 is of no consequence; in this it is a question of cumula- 

 tive or functional adaptation. Experimental proofs of 

 this are difficult to find, if one wants a strict demonstra- 

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