170 LAWS OF VARIATION. Chap. V. 



Whatever the cause may be of each slight difference 

 in the offspring from their parents — and a cause for 

 each must exist — it is the steady accumulation, through 

 natural selection, of such differences, when beneficial to 

 the individual, that gives rise to all the more important 

 modifications of structure, by which the innumerable 

 beings on the face of this earth are enabled to struggle 

 with each other, and the best adapted to survive. 



