HOMOLOGY AND ITS INTERPRETATION 45 



the specifications of a progressive step in evolution. Hence he 

 suggests that the chromosomal mutation is subsequently sup- 

 plemented by appropriate factorial mutation. Once this sup- 

 position is made, however, all the objections we have 

 mentioned in connection with factorial mutation [e.g the 

 subnormality of its products, its intra-specific nature, etc.) 

 return to plague the speculator, and, in addition to these, he 

 is confronted with the new difficulty of explaining how the 

 redundance of duplicate genes can be removed and replaced by 

 coordinate differentiation in their respective specificities. Now 

 we have no factual evidence whatever of such a solidaric re- 

 differentiation of the germinal factors, that would modify 

 harmoniously the composition and role of each and every 

 gene in the factorial complex. Nor is there any possibility 

 whatever of accounting for this telic superregulation of the 

 germinal regulators upon a purely mechanistic basis. How 

 can the ultimate chemical determinants of heredity be thus 

 redetermined? Consequently, although there is gametic in- 

 compatibility between diploid races and the tetraploid races, 

 which are said to have arisen from the former, we are not, 

 nevertheless, warranted, by what has been experimentally 

 verified, in regarding tetraploid races as new species, or as 

 progressive steps in the process of organic evolution. 



To conclude, therefore, we have experimental verification 

 of the efficacy of the similifying process said to have been at 

 work in evolution, namely, inheritance. The same, however, 

 cannot be said of the correlative diversifying process of trans- 

 specific variation, which is said to have superficially modified 

 old structures into new species. The latter process, accord- 

 ingly, is but a pure postulate of science known to us only 

 through the effect hypothetically assigned to it, namely, the 

 adaptive modification. 



The adaptation, however, of which there is question here is 

 not to be confounded with the *^ acquired adaptation" of 

 Lamarckian fame; for, unlike the latter, it is an inheritable 

 modification rooted in the germ plasm. Adaptations of this 



