5 8 THE POPULAR SCIENCE MONTHLY. 



among them consequent on the likeness of their respective relations to 

 the matters and forces around ; and there will result, in some cases, 

 the differences due to the differential effects of these matters and 

 forces, and in other cases, the changes which, being life-sustaining or 

 life-destroying, eventuate in certain natural selections. 



I have, above, made a passing reference to the fact that Mr. Dar- 

 win did not fail to take account of some among these effects directly 

 produced on organisms by surrounding inorganic agencies. Here are 

 extracts from the sixth edition of the Origin of Species showing this. 



" It is very difficult to decide how far changed conditions, such as of climate, 

 food, &c, have acted in a definite manner. There is reason to believe that in 

 the course of time the effects have heen greater than can he proved by clear 

 evidence. . . . Mr. Gould believes that birds of the same species are more 

 brightly coloured under a clear atmosphere, than when living near the coast or 

 on islands; and Wollaston is convinced that residence near the sea affects the 

 colours of insects. Moquin-Tandon gives a list of plants which, when growing 

 near the sea-shore, have their leaves in some degree fleshy, though not elsewhere 

 fleshy " (pp. 106-7). " Some observers are convinced that a damp climate af- 

 fects the growth of the hair, and that with the hair the horns are correlated " 

 (p. 159). 



In his subsequent work, Animals and PIa?its under Domestication, 

 Mr. Darwin still more clearly recognizes these causes of change in or- 

 ganization. A chapter is devoted to the subject. After premising 

 that "the direct action of the conditions of life, whether leading to 

 definite or indefinite results, is a totally distinct consideration from the 

 effects of natural selection ; " he goes on to say that changed condi- 

 tions of life " have acted so definitely and powerfully on the organiza- 

 tion of our domesticated productions, that they have sufficed to form 

 new sub-varieties or races, without the aid of selection by man or of 

 natural selection." Of his examples here are two. 



" 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 genera- 

 tions." (Vol. ii, p. 277.) [And in this ninth chapter concerning these and 

 other such instances he says " some of the foregoing differences would certainly 

 be considered of specific value with plants in a state of nature." (Vol. i, p. 

 321.)] "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 same garden and under as nearly as possible 

 the same conditions." And then enumerating six traits in which the American 

 forms all of them differ in like ways from their allied European forms, Mr. Dar- 

 win thinks there is no choice but to conclude that these "have been definitely 

 caused by the long-continued action of the different elimate of the two conti- 

 nents on the trees." (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 



