The Unity of the Organism 



facts connected with heredity, even though no causal ex- 

 planation of them is forthcoming. 



The childlikeness, as Conklin well characterized it, of 

 the belief that chromosomes are a simple and complete ex- 

 planation of inheritance would not be so bad in itself. If 

 it stopped there, as genuine childlikeness would, no posi- 

 tive harm could be done. It is the making of this belief 

 the starting point of a grand speculation which blinds the 

 eyes and closes the mind to a vast number of facts and 

 legitimate inferences about heredity, that plays havoc with 

 thinking on genetics. It would be a great gain if gen- 

 etic theory would recognize wholeheartedly that all or- 

 ganic development, as contrasted with mere enlargement, 

 consists more fundamentally and obviously in transforma- 

 tion of substances than it does in unchanged continuity of 

 substances. For under such recognition the futility of 

 attempting to explain the transformation of one lot of 

 substance by referring it to another lot which does not 

 transform, or in other words to explain development by 

 something that does not itself develop, would be manifest. 



That the chromosome theory of heredity in reality deep- 

 ens rather than illumines the darkness which surrounds the 

 problem is seen when one reflects that not only does it 

 throw no light on the question of how the chromosomes come 

 to be bearers of heredity, but that it creates the new and 

 equally difficult question of how the chromosomes (which ac- 

 cording to the theory maintain unchanged their individuality 

 not only from generation to generation but throughout each 

 ontogeny) are yet able to be causally operative in the cell- 

 bodies undergoing the transformations which they actually 

 do undergo in the developing organism. That the germ- 

 plasm-chromosome theory of heredity could have led its 

 devotees to sidestep the details of ontogeny, especially those 

 of histogenesis, to the extent which our review has shown 

 it to have done, would be unbelievable but for what is 



