98 HEREDITY AND VARIATION 



in observing the actual origin by mutation of stable new varieties 

 or subspecies of (Enothera lamarckiana and some other plants ; 

 in showing by historical research combined with experiment 

 that many stable stocks of cultivated plants have arisen by 

 mutation ; and by corroborating throughout the fundamental 

 idea that " the characters of organisms are composed of units 

 sharply distinguished from one another." 



The contrast between fluctuations and mutations is so im- 

 portant that we may state it once more, (i) Fluctuations 

 are continually occurring generation after generation : mutations 

 are rare and occur intermittently. (2) Fluctuations give rise 

 to a series of minute differences which may be arranged on a 

 frequency curve, according to the laws of chance : mutations 

 may be large or small, and their occurrences do not illustrate any 

 ascertained law of frequency. (3) Fluctuations do not lead to a 

 permanent change in the mean of the species unless there be 

 very rigorous selection, and even then, if the selection be slackened, 

 there is regression to the old mean : mutations lead per saltum 

 to a new specific position, and there is no regression to the old 

 mean. (4) Fluctuations do not yield anything really new, they 

 imply a little more or a little less of characters already present : 

 mutations are novelties, they imply some new pattern, some 

 new position of organic equilibrium. According to De Vries's 

 theory, no new species can be established without mutation. 

 " When a mutation has occurred a new species is already in 

 existence, and will remain in existence, unless all the progeny 

 of the mutation are destroyed." .... The phrase " survival 

 of the fittest," as describing a process of evolution, ought to be 

 replaced by " survival of the fittest species." According to De 

 Vries, species originate by mutation instead of by the continuous 

 selection of fluctuations. " Natural Selection may explain the 

 survival of the fittest, but it cannot explain the arrival of the 

 fittest." 



In regard to these far-reaching conclusions it should be noted 



