318 THE THEORY OF THE GENE 



has a specific effect on the course of development, and 

 this is not inconsistent with the point of view urged 

 above, that all the genes or many of them work together 

 toward a definite and complicated end-product. 



The best argument at present in favor of a specific 

 action of each gene is found in the series of multiple alle- 

 lomorphs. Here changes in the same locus affect pri- 

 marily the same end-result not only in one organ, but in 

 all the parts that are also visibly affected. 



Is the Mutation Process Due to a Degradation 



of the Genef 



In his mutation theory de Vries spoke of types that we 

 now call mutant recessive types as arising from the loss 

 or inactivation of genes. Such changes he regarded as 

 retrogressive. At about the same time, or a little later, 

 the idea that recessive characters are due to losses of 

 genes from the germ material became popular. At the 

 present time several critics interested primarily in the 

 philosophical discussion of evolution have attacked with 

 violence the idea that the mutant types studied by geneti- 

 cists have anything to do with the traditional theory of 

 evolution. With this latter assertion we are not much con- 

 cerned, and may safely leave the question at issue for the 

 future to decide; but the suggestion that the mutation 

 process, in so far as it involves an effect on single genes, 

 is limited to the loss of genes or to their partial loss or 

 degradation, as I venture to call such a change, is a mat- 

 ter of some theoretical interest; for, as Bateson elabo- 

 rated in his 1914 address, it leads logically to the idea 

 that the materials that we use in genetic work are due to 

 loss of genes; that absences, in a literal sense, are the 

 allelomorphs of wild type genes ; and that, in so far as 

 this evidence applies to evolution, it leads to the reductio 



