EVOLUTION AND 

 GENIC ACTION 



I have been reproached for not having made it clear in my book 

 The Material Basis of Evolution whether I was speaking of systemic 

 mutation (scrambhng of the chromosomal pattern) or of ordinary 

 mutations of a macroevolutionary type, and of being confused myself 

 on what I meant. Such criticism is based upon misunderstanding of 

 the logic of the argument. We just derived the meaning of systemic 

 mutation and its origin. In the extremest case, it would mean a 

 complete repatterning of the genome in one or a few steps. In a less 

 extreme case, it might mean a partial repatterning of one or two 

 chromosomes of the type found in the differences between two still 

 crossable species of Drosophila. But there is no clear delimitation of 

 such a lower grade of repatterning from still lower ones. The lowest 

 grade is an ordinary "genie mutation" which I consider to be a tiny 

 repatterning on a submicroscopic level. From the point of view of 

 action of the genie material there is so far no possibility of studying 

 the differences brought about by a hypothetical systemic mutation; 

 but we can study the difference at the lower end of the series, the 

 simple mutation. Such a study can give us a model for the action of a 

 systemic mutation, if we find mutants, macromutants, which produce 

 such a large deviation from normal that they show in their limited 

 action upon a part of the body (but sometimes also the entire 

 organism, e.g., corn grass) what can be accomplished within the 

 framework of viable development in regard to huge deviations, ac- 

 complishing in one step a real saltation of the kind we would expect 

 to be produced by a systemic mutation. The argument is to show, 

 with the model of the macromutant, that big saltatory deviations 

 from normal are possible within the normal potentialities of develop- 

 ment. If this can be shown, the facts not only serve as a model of 

 macroevolutionary changes but demonstrate the possibility, in princi- 

 ple, of saltations in evolution, which might be due to systemic 

 mutations, leading, in rare cases, to a viable whole. It is regrettable 

 that many evolutionists forget that the developmental potencies are 

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