Mutations and Evolution 397 



no jumps. We had become accustomed, also, in the discus- 

 sion of economic and poUtical ideas, to contrast " evolution '* 

 with " revolution." So many of us were evolutionists in the 

 comfortable indifference that was satisfied to leave every- 

 thing to ** natural law," that every change proposed threat- 

 ened to be '* revolutionary." Along came de Vries at the 

 end of the century and said in effect that this acceptable 

 process of evolution is actually a step by step process — and 

 each step is a revolution! 



This point of view had in the meantime made a congenial 

 place for itself in the minds of many people through the 

 development of new theories regarding the constitution of 

 matter. Whereas the elementary approach to the constitu- 

 tion of matter assumes a certain continuity, the atomic 

 theory at the end of the Eighteenth Century started to ac- 

 custom the civilized world to the idea that matter is made 

 up of infinitely small disconnected particles. But a century 

 later investigators were already at work breaking the atom 

 up into still smaller hypothetical units, with a still greater 

 proportion of empty space. These newer theories of mat- 

 ter emphasized especially not merely the discontinuity of 

 matter as an existing something, but also the discontinuity 

 in the change of one kind of matter into another. Every- 

 thing goes, when it goes at all, by jumps. 



Perhaps this theory of evolution, like its predecessors, 

 will also have to yield to increased knowledge. At the pres- 

 ent time it harmonizes not only with the relevant facts of 

 observation and experiment, .but with the temper of the 

 scientific world. Our reliance upon " natural laws " and 

 upon the principle of uniformity have become reconciled to 

 accepting the " new " as a normal outcome of the " old." 



