ORIGIN OF MUTANT CHARACTERS 67 



chemical sense) of the gene. Tempting as is this com- 

 parison, we must remember that, as yet, we have almost 

 no evidence as to the real nature of the mutation process. 



The mutant types that are most often referred to, or 

 used for genetic material, are as a rule rather extreme 

 modifications or aberrations. This has sometimes given 

 the impression that a mutant change involves a great 

 departure from the original type. Darwin spoke of salta- 

 tions, which are only extreme mutations, and he rejected 

 them as materials for evolution, because, he said, such 

 great alterations in one part of the body would be likely 

 to throw the organism out of harmony with its environ- 

 ment, to which it is nicely adapted. Today, while we real- 

 ize fully the truth of this statement, when applied to 

 extreme changes producing malformations or aberra- 

 tions, we have come, nevertheless, to a realization that 

 minute changes are as characteristic of mutation as are 

 the grosser changes. In fact, it has been shown many 

 times that small changes that make a part a little larger 

 or a little smaller may also be due to genes in the germ- 

 material. Since only the differences that are due to genes 

 are inherited, it seems to follow that evolution must have 

 taken place through changes in the genes. It does not 

 follow, however, that these evolutionary changes are 

 identical with those that we see arising as mutations. It is 

 possible that the genes of wild types have had a different 

 origin. In fact, this view is often implied and sometimes 

 vigorously asserted. It is important, therefore, to find 

 out whether there is any evidence in support of such a 

 view. De Vries' earlier formulation of his famous muta- 

 tion theory might at first sight seem to suggest the crea- 

 tion of new genes. 



The opening sentence of the mutation theory states 

 "that the properties of the organism are made up of 

 units, sharply distinguishable from one another. These 



