14 CONTACTS WITH DARWINISM I [ch. ii 



The hypothesis of evolution by small variation has never, so to 

 speak, been officially abandoned, but it has been so altered by 

 supplementary hypotheses that it is hardly recognisable, and the 

 theory of mutation, brought up by de Vries, has largely taken its 

 place. A mutation, which when obvious is often called a sport, 

 at once produces a morphological or structural character or 

 characters that are definitely distinct from those which were 

 found in the parent form, and not only that, but which have come 

 to stay, and are (practically) irreversible. It is always possible, 

 of course, though not very probable, that some later mutation 

 may change them, or some of them, back again, or to something 

 else. Here, then, was a hypothesis that surmounted the chief 

 difficulties mentioned above, and provided hereditary variations 

 that were differentiating and (practically) irreversible. 



Mutation was taken up, though slowly, as people gradually 

 realised the fatal nature of the objections to linear and infinitesi- 

 mal variations. Unfortunately for its speedy success, some doubt 

 was thrown upon the genuinely mutational nature of the pheno- 

 mena upon which it based. Some, at any rate, appeared to have 

 been due to hybridisation. But in spite of this setback, mutation 

 had come to stay, and we shall trace some of its history below. 

 People say that a sport is not capable of succeeding by itself, but 

 we do not know what would happen if it were really viable, and 

 plenty of time were allowed. 



Natural selection was, of course, essentially a theory of gradual, 

 progressive, and more or less continuous adaptation to sur- 

 rounding conditions. It is evident that living things are suited 

 to them, for if they were not they would soon be killed out in the 

 struggle for existence. Some theory that will explain adaptation 

 is, therefore, very desirable. It was largely because it seemed so 

 capable of doing this that natural selection was so enthusiastically 

 taken up. 



Each new species was formed, according to Darwin, because it 

 was an adaptational improvement upon its immediate ancestor. 

 Once this was fully realised, there was a great rush into the study 

 of adaptation. It was taken for granted (it could hardly be 

 otherwise) that as natural selection was trying to explain evolu- 

 tion, which showed itself mainly in external structural characters, 

 these characters must also, of necessity, be the means of expres- 

 sion of adaptation. Evolution has undoubtedly gone on in 

 morphological change, but as yet we are practically without any 

 proof that the change also represents the adaptation that may 



