VARIATION. 329 



there must be some cause for these apparently-spontaneous 

 variations, but it seems to me that a definite cause is assign- 

 able. I think it may be shown that unlikenesses must neces- 

 sarily arise even between the new individuals simultaneously 

 produced by the same parents. Instead of the occurrence 

 of such variations being inexplicable, the absence of them 

 would be inexplicable. 



In any series of dependent changes a small initial differ- 

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

 in which a particular breaker bursts on the beach, may deter- 

 mine 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 matter, may set up an immensely- 

 involved set of functional disturbances and structural alter- 

 ations. 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 difference in the direction of some soldier's 

 musket at the battle of Arcola, by killing Napoleon, might 

 have changed events throughout Europe ; and though the type 

 of 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 is 

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



