278 THE EVOLUTION OF SEX. 



evolution emphasized the growing or evolving powers of the organ- 

 isms themselves, which developed in rhythmic impulses through 

 ascending grades of organization, modified at the same time by 

 external circumstances, which acted with most effect on the generative 

 system. It is difficult indeed to refrain from amusement or irritation 

 at the naive simplicity with which he evolves a mammal from a bird, 

 by the short and easy method of prolonging the period of uterine 

 life in favorable nutritive conditions; but though a goose could not 

 so simply give rise to a rat, the emphasis laid on the influence of pro- 

 longed gestation is full of suggestiveness, especially in relation to the 

 evolution of mammals. Apart from his common-sense view of evo- 

 lution as a process of continued growing, Chambers deserves to be 

 remembered as one of the first to appreciate ' ' the force of certain 

 external conditions operating upon the parturient system." 



In France, Geoffroy and Isdore St. Hilaire — father and son — 

 denied indefinite variations, regarded function as of secondary 

 importance, and laid special stress upon the direct influence of the 

 environment. To them it seemed not so much the effort to fly, as 

 the (supposed) diminished proportion of carbonic acid in the atmos- 

 phere, which had determined the evolution of birds from ancient 

 reptiles. A complete history of evolution theories, up to the publica- 

 tion of " The Origin of Species" (1859), would have to take account 

 further of the opinions of the geographer Von Buch and the embry- 

 ologist Von Baer, of Schleiden and Naudin, Owen, and Carus, and 

 many others; but no such survey is here our purpose. 



For it must be already evident from the above brief sketch of 

 representative opinions that successive naturalists have emphasized 

 now one factor and now another in the evolutionary process. To one 

 it seemed as if the organism had a motor power of development — 

 often a metaphysical one, it must be allowed — within itself, and that 

 ev )lution was to be explained, in Topsian fashion, "according to the 

 laws of organic growth' ' ; to another, function appeared all-important, 

 perfecting organs on the one hand, allowing them to wane in disuse on 

 the other; to a third, organisms were seen under the hammers of 

 external forces and circumstances, being continuously welded in more 

 and more perfectly adapted forms. The organism, its function, and 

 its environment, on each of the three factors in the problem . emphasis 

 was in turn laid. 



At this juncture Darwin elaborated his theory of " The Origin of 

 Species by means of Natural Selection and the Preservation of 

 Favored Races in the Struggle for Life," and was independently and 

 simultaneously corroborated b y Al fred Russel Wallace. They. did not 

 i ndeed deny a spontaneous power of change in t he organism itself, nor 



