18 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 new described as the science 
of biometry. 
