THE CAUSES OF THE STRUGGLE. 309 



this but is too old to change ; it is the germ which 

 is sufficiently impressionable to do this. After all 

 it is only another experience of the continuous 

 being, and differs little from the changes going on 

 every day except that the infant is more plastic 

 and more affected by the circumstance. We might 

 go on quoting examples, but plenty of these will 

 occur to the mind of the naturalist Some will 

 perhaps say that there are cases where no benefit 

 can possibly arise from particular variations. We 

 can never be quite sure that this objection is valid, 

 and even were it the case it is easy to conceive 

 that mistakes are made sometimes. It would be 

 strange indeed if nature were faultless in this 

 respect, seeing that man with all his instincts and 

 higher development of reasoning power continues 

 to err. And every mistake entails its own con- 

 sequences which are often disastrous while natural 

 selection perpetuates the most useful variations. 



From these premises it appears to us that the 

 key to variation is continuity. The experiences of 

 every past generation is embodied in every living 

 thing, and each one of these affects the offshoot 

 more or less. To these are added, in the course 

 of its own life, a thousand others, and when its most 

 critical period arrives and the bud which goes to 

 make up a new being is particularly sensitive, 



