3.20 THE EVOLUTION THEORY 



since Darwin and Wallace has been almost exclusively devoted — I 

 mean the origin of adaptations. Not that he does not mention these, 

 he assumes in regard to his mutations ' a selection working in a con- 

 stant direction,' and seeks to interpret them in terms of it, but as the 

 mutations occur from purely internal reasons — I mean without any 

 connexion with the necessit}' for a new adaptation — and occur only in 

 a small percentage of individuals, and in no definite direction, they 

 cannot possil)l3" suffice to explain adaptation, which seems to dominate 

 the whole organic world. But this is precisely the point at which 

 many botanists cease to understand the zoologists, because among 

 plants there are fewer adaptations than among animals ; or, in any 

 case, adaptations in plants are not so readily demonstrated as among 

 animals, which not infrequently seem to us to be entirely built up 

 of adaptations. 



In this book, and in this chapter itself, I have discussed adapta- 

 tions and their origin so much already that I need only refer to these 

 pages for convincing evidence that we cannot think of them as being 

 lirought aV)Out by the accumulation and augmentation of individually 

 occurrino- saltatorv ' mutations.' Not even if we assume that the 

 leaps of mutation can be increased in the course of generations ; in 

 short, even if we say that mutations are all those variations which 

 breed true and lead to the development of species, while variations 

 are those which do not. This Avould onl}^ be playing with words, so 

 let us say that the fluctuating variations are really different in their 

 nature, that is, in their causes, from mutations. De Vrie s lays great 

 stress on the fact that these two kinds of va riations must be sharpl}'- 



^distinguished from one another, and this may hayebeen useful or 

 necessary for the first investigation of the facts before him, for we 

 must first analyse and then recombine, but that variations and 

 mutations are in reality different in nature can assuredly not be 



' assumed, since innumerable adaptations can only have arisen through 

 the auQfmentation of individual variations. These must therefore be 

 able to become 'pure breeding,' even although they may not have 

 done so in the cases of artificial selection which have hitherto been 

 observed. How is it possible that chance mutations, in no pai'ticular 

 direction, occurring onl}' rarely and in a small percentage of indi- 

 viduals, can explain the origin of the leaf-marking of a Kallhna or 

 an Ancea — the shiftinji; of the original wing-nervures to form leaf- 

 veins, and the exact correlation of these veins across the surfaces of 

 both pairs of wings ? And even if we were to admit that a mutation 

 mifrht have occurred which caused the veins of the anterior and 

 posterior wings to meet exactly by chance, that would still not be 



