182 THE STOKY OF LIFE'S MECHANISM. 



Of the fact of these variations there is no 

 question, and the matter need not detain us. 

 Every one has had too many experiences to ask 

 for proof. Of the nature of the variations, how- 

 ever, there are some points to be considered 

 which are very germane to our subject. In the 

 first place, we must notice that these variations 

 are of two kinds. There is one class which is 

 born with the individual, so that they are 

 present from the time of birth. In saying that 

 these variations are born with the individual we 

 do not necessarily mean that they are externally 

 apparent at birth. A child may inherit from its 

 parents characters which do not appear till adult 

 life. For example, a child may inherit the colour 

 of its father's hair, but this colour is not apparent 

 at birth. It appears only in later life, but it is 

 none the less an inborn character. In the same 

 way, we may have many inborn variations among 

 individuals which do not make themselves seen 

 until adult life, but which are none the less 

 innate. The offspring of the same parents may 

 show decided differences, although they are put 

 under similar conditions, and such differences are 

 of course inherent in the nature of the individual. 

 Such variations are called congenital variations. 



There is, however, a second class of variations 

 which are not born in the individual, but which 

 arise as the result of some conditions affecting its 

 after-life. The most extreme instances of this 

 kind are mutilations. Some men have only one 

 leg because the other has been lost by accident. 

 Here is a variation acquired as the result of 

 circumstances. A blacksmith differs from other 



