PRIMA R Y FA CTORS IN E VOL UTION. 83 



ator of biologist and physicist alike is as inexpressibly 

 marvellous as the philosopher's greatest common measure. 

 There are at least two great problems in evolution : — 



(A) How do changes or variations arise ? 



(B) How do these variations become new, well- 

 adapted, progressive species ? 



A. The Pritiiary Factors in Evolution — which will 

 account for the origin of variations. 



It is well to recognise that this is the fundamental prob- 

 lem. Unless we can give some theory of the origin of 

 variations, we have no material for further construction. 

 Unfortunately we are very ignorant about the whole matter. 

 But, in the first place, it is quite certain that the environ- 

 ment in the widest sense must be the primary cause of 

 changes in animals. So far almost all naturalists are 

 agreed. Thus Herbert Spencer says, " The action of the 

 environment is the primordial factor in organic evolution," 

 and Weismann traces the origin of variations in the long run 

 to the action of the environment upon the simplest organ- 

 isms. By the environment we mean all external influences 

 — mechanical, chemical, physical ; pressure, moisture, 

 aeration, heat, light, and also food. [It is indeed possible 

 that there are environmental influences of which our senses 

 are unaware, — the " spiritual influxes " of which Wallace 

 speaks, but these are obviously beyond the scope of scientific 

 analysis.] * 



That all variations are ultimately due to the action of 

 the environment in the widest sense, we regard as an axiom. 

 But in regard to the direct conditions of organic change, 

 naturalists are or ought to be very uncertain. I shall state 

 the possibilities. 



* It seems to me desirable to avoid talking about the " principles of 

 evolution," e.g., as variability, heredity, and natural selection, or as 

 variability, heredity, isolation. Not only are words like " principle " 

 used in the loosest possible way, but they suggest a conclusiveness which 

 certainly does not exist, and they are apt to become intellectual 

 fetishes. Variability is only a term for the tendency organisms have to 

 vary, the conditions of variation being numerous and obscure. Similarly, 

 heredity is only a term for the relation of organic continuity between 

 successive generations. 



