46 THE FACTORS OF ORGANIC EVOLUTION. 



productions, that they have sufficed to form new sub- 

 I varieties or races, without the aid of selection by man or 

 ( of natural selection.&quot; Of his examples here are two. 



&quot; I have given in detail in the ninth chapter the most remarkable case 

 known to me, namely, that in Germany several varieties of maize brought 

 from the hotter parts of America were transformed in the course of only 

 two or three generations.&quot; (Vol. ii, p. 277.) [And in this ninth chapter 

 concerning these and other such instances he says &quot; some of the foregoing 

 differences would certainly be considered of specific value with plants in a 

 state of nature.&quot; (Vol. i, p. 321.)] &quot; Mr. Meehan, in a remarkable paper, 

 compares twenty-nine kinds of American trees, belonging to various orders, 

 with their nearest European allies, all grown in close proximity in the 

 Bame garden and under as nearly as possible the same conditions.&quot; And 

 then enumerating six traits in which the American forms all of them differ 

 in like ways from their allied European forms, Mr. Darwin thinks there is 

 no choice but to conclude that these &quot; have been definitely caused by the 

 long-continued action of the different climate of the two continents on the 

 trees.&quot; (Vol. ii, pp. 281-2.) 



But the fact we have to note is that while Mr. Darwin 

 thus took account of special effects due to special amounts 

 and combinations of agencies in the environment, he did 

 not take account of the far more important effects due to 

 the general and constant operation of these agencies.* If 

 a difference between the quantities of a force which acts 

 on two organisms, otherwise alike and otherwise similarly 

 conditioned, produces some difference between them; then, 

 by implication, this force produces in both of them effects 



* It is true that while not deliberately admitted by Mr. Darwin, these 

 effects are not denied by him. In his Animals and Plants under Domesti 

 cation (vol. ii, 281), he refers to certain chapters in the Principles of 

 Biology, in which I have discussed this general inter-action of the medium 

 and the organism, and ascribed certain most general traits to it. But 

 though, by his expressions, he implies a sympathetic attention to the 

 argument, he does not in such way adopt the conclusion as to assign 

 to this factor any share in the genesis of organic structures much less 

 that large share which I believe it has had. I did not myself at that 

 time, nor indeed until quite recently, see how extensive and profound have 

 been the influences on organization which, as we shall presently see, are 

 traceable to the early results of this fundamental relation between organism 

 and medium. I may add that it is in an essay on &quot; Transcendental 

 Physiology,&quot; first published in 1857, that the line of thought here followed 

 out in its wider bearings, was first entered upon. 



