THE EPIC OF EVOLUTION 525 



Another theoretical escape from the dilemma is furnished by. the 

 assumption that the variations employed in survival are not all made 

 out of accumulations of the useless sort, which are often transitory 

 effects of the environment and not heritable, but are a particular 

 kind of variation that is of hereditary significance from the start. 

 Evidence of the existence of such a distinctive kind of germinal 

 variation, whose transmissibility is not questionable, has been 

 furnished by the Dutch botanist Hugo DeVries (1846-1935) in his 

 book entitled Die Mutationstheorie. By chance DeVries discovered 

 among some wild evening primroses, Oenothera, certain individuals 

 so decidedly different from the original type that they would be 

 regarded by a botanist as distinct species if the history of their 

 origin was not known. There was evidence that these new forms 

 did not evolve gradually, but that they appeared suddenly with no 

 warning of imminent change. Moreover, when isolated they repro- 

 duced their distinctive characteristics. Variations of this kind that 

 breed true DeVries called mutations. 



It is now known that the occurrence of mutations is widespread 

 among both plants and animals. Several hundred distinct mutations, 

 for example, have been described from the much-studied fruit fly, 

 Drosophila, alone. Mutations may be useless or useful in survival, 

 but in any case they are heritable and thus furnish raw materials 

 for the selection mill. In other words, all mutations must still run 

 the gauntlet of natural selection. 



DeVries' theory made it clear that it is not necessary to wait for the 

 slow accretions of insignificant useless chance variations to provide 

 characteristics of selective value, since mutations furnish the necessary 

 materials which evolution demands, ready made and transmissible. 

 Thus, existing organisms are to be regarded as the sum of the muta- 

 tions that have survived since the dawn of life. 



The reality of mutations has been amply demonstrated. The 

 causes of this type of variation, however, are still a matter for further 

 study and investigation, in which considerable progress has already 

 been made. It is likely, furthermore, that the mutations of DeVries 

 do not represent the introduction of something entirely new. but 

 rather a new combination of characters already present. The great 

 service of DeVries' work lies in the fact that the explanation of the 

 method of evolution has been shifted by means of it from the un- 

 scientific field of argument to the more scientific and dependable 

 field of experimentation. 



