414 OUTLINES OF EVOLUTIONARY BIOLOGY 



which are merely of a pins or minus character the changes which 

 we call mutations are given off in almost every manner of new 

 direction. They only appear from time to time, their periodicity 

 being probably due to perfectly definite but hitherto undiscovered 

 causes. 



" The theory of the inheritance of acquired characters comes 

 under the heading of fluctuations. Acquired characters have 

 nothing to do with the origin of species. Nor can the theory of 

 descent be applied to the solution of social problems." l 



There is here no suggestion of a hybrid origin for the 

 mutations in question. If, however, as seems probable, a large 

 proportion of so-called mutations are really the result of hybridi- 

 zation, and if, as we showed in Chapter XIV, hybrids tend to be 

 automatically eliminated in a state of nature though of course 

 there is nothing to prevent a constant hybrid from being pre- 

 served if it happens to possess characters peculiarly favourable 

 to its own existence it does not seem likely that such mutations 

 can have played any very great part in organic evolution. In 

 any case there is no need to suppose that the theories of muta- 

 tion and natural selection are mutually exclusive, for, however 

 new characters may arise, they must be subject to the action of 

 natural selection in the struggle for existence. 



Professor de Vries' objection to small, fluctuating variations as 

 the material upon which natural selection operates in the 

 modification of species appears to be based upon the view that 

 such characters are acquired in the lifetime of the individual 

 and cannot be inherited. If, however, we admit that a sorna- 

 togenic character may, in the course of many generations 

 and under the continued influence of the same conditions which 

 originally called it forth, become converted into a blastogenic 

 character, this difficulty entirely disappears. 



It is extremely hard to believe that mutations, which, apart 

 from the occurrence of hybridization, seem to occur very rarely 

 and at long intervals, can have afforded sufficient opportunity 

 for the production of all the marvellous adaptations which exist 

 in nature. Take, for example, the mutual adaptations which we 

 see between the length of the nectary in certain flowers and the 

 length of the proboscis in the insects which fertilize them. We 

 cannot suppose that either the elongated nectary or the elongated 

 proboscis arose by sudden mutations, for unless these mutations 



1 " The Mutation Theory." English Trans., Vol. I., p. -'13. 



