i8 INTRODUCTION 



than their predecessors will survive, whilst those which 

 are worse will be destroyed by the action of natural 

 selection. 



Thus it would be an appropriate use of this concep- 

 tion to seek in a mutation the explanation of the final 

 loss of the much reduced limbs presumably exhibited 

 by comparatively recent ancestors of the family of 

 snakes. This final loss is especially difficult to under- 

 stand on the Darwinian theory. Moreover, changes of 

 a closely similar nature are not hypothetical, but have 

 actually been observed to take place. At the same 

 time it must not be supposed that mutations are con- 

 fined to the loss of pre-existing organs ; indeed, the 

 origin of a totally new organ is quite inexplicable on 

 either of the two preceding theories. The very first 

 inception of such an organ must, it would seem, of 

 necessity be sudden. 



After giving some account of the earlier theories of 

 evolution, we shall next proceed to treat of those sub- 

 jects with which we are more properly concerned 

 that is to say, the recent experimental observations 

 on variation and natural inheritance, together with 

 their bearing on the theories of evolution. And in the 

 first place we shall describe some recent studies which 

 are not strictly experimental, but which nevertheless 

 deal to some extent with actual facts namely, the 

 statistical study of variations, particularly of con- 

 tinuous variations. This subject has been dignified 

 by a special name, and is now described as the science 

 of biometry. 



