Organic Evolution. 233 



early days of organic evolution : how can we, then, pre- 

 tend to understand their origins ? 



If we speculate at all on the matter, we are led to the 

 view that the variations must be primarily due to the 

 differential incidence of mechanical stresses and physical 

 or chemical influences. It may be admitted that this is 

 little more than saying that they are due to some physical 

 cause. Still, this at least may be taken as certain for 

 what it is worth that the primitive tissue-differentiations 

 are due to physical or chemical influences, direct or indirect, 

 on the protoplasm of the cell. Here is one mode of the 

 origin of variations. 



I do not wish to reopen the question whether these" 

 variations originate in the germ or in the body. I content 

 myself with indicating the difference, from this standpoint, 

 between the two views. Take, for example, the end-organs 

 of the special senses, which respond explosively to physical 

 influences in- ways we shall have to consider more fully in 

 the next chapter. If we hold that variations originating 

 in the body may be transmitted through the germ to the 

 offspring, then we may say that these variations are the 

 direct result of the incidence of the physical or molecular 

 vibrations on the protoplasm. But if we believe, with 

 Professor Weismann, that all variations originate in the 

 germ, then the variations in the end-organs of the special 

 senses, fitting them to be the recipients of special modes of 

 influence, result from physical effects upon the germ of 

 purely fortuitous origin, that is to say, wholly unrelated to 

 the end in view. The rods and cones of the retina are due 

 to purely chance variations, impressed by some chemical 

 or physical causes completely unknown on the germinal 

 protoplasmic substance. Those individuals which did not 

 have these chance variations have been eliminated. It 

 matters not that the rods and cones are believed to have 

 reached their present excellence through many intermediate 

 steps from much simpler beginnings. The fact remains 

 that the origin of all these step-like variations was fortui- 

 tous, and not in any way the direct outcome of the physical 



