VARIATION. 263 



variations being inexplicable, we shall presently see that the 

 absence of them would be inexplicable. 



In any series of dependent changes, a small initial difference 

 often works a marked difference in the results. The mode in 

 which a particular breaker bursts on the beach, may determine 

 whether the seed of some foreign plant which it bears, is or is not 

 stranded may cause the presence or absence of this plant from 

 the Flora of the land; and may so affect, for millions of years, in 

 countless ways, the living creatures throughout the land. A 

 single touch, by introducing into the body some morbid mat- 

 ter, may set up an immensely- involved set of functional dis- 

 turbances and structural alterations. The whole tenor of a life 

 may be changed by a word of advice ; or a glance may 

 determine an action which alters thoughts, feelings, and 

 deeds throughout a long series of years. In. those still more 

 involved combinations of changes which societies exhibit, 

 this truth is still more conspicuous. A hair's-breadth differ- 

 ence in the direction of some soldier's musket at the battle of 

 Arcola, by killing Napoleon, might have changed events 

 throughout Europe : though the social organization in each 

 European country, would have been now very much what it 

 is, yet in countless details it would have been different. 



Illustrations like these, with which pages might be filled, 

 prepare us for the conclusion, that organisms produced by 

 the same parents at the same time, must be more or less 

 differentiated both by insensible initial differences, and by 

 slight differences in the conditions to which they are subject 

 during their evolution. "We need not, however, rest with 

 assuming such initial differences : the necessity of them i& 

 demonstrable. The individual germ- cells which, in succes- 

 sion or simultaneously, are separated from the same parent, 

 can never be exactly alike ; nor can the sperm-cells which 

 fertilize them. When treating of the instability of the 

 homogeneous (First Principles, 109), we saw that no two 

 parts of any aggregate, can be similarly conditioned with 



