THE REPRODUCTIVE FACTOR IN EVOLUTION. 303 



For it must be already evident from the above brief sketch 

 of representative opinions, that successive naturalists have 

 emphasised now one factor and now another in the evolu- 

 tionary 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 evolution 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 con- 

 tinuously 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 Favoured Races in the Struggle for Life," and 

 was independently and simultaneously corroborated by Alfred 

 Russel Wallace. They did not indeed deny a spontaneous 

 power of change in the organism itself, nor the influence of 

 function and environment; but, without definitely discussing 

 the origin of variations, sought to show how the destructive or 

 eliminating, and the conservative or selecting agency of the 

 animate and inanimate environment, were the principal factors 

 in evolution. Given a sufficient crop of indefinite variations, 

 — unanalysed or unanalysable as to their origin, — the struggle 

 for existence separated the minority of wheat ears from the 

 majority of tares, and secured a finer and finer harvest. 



So much had Darwin in his magistral labours to do with 

 making the general conception of evolution current coin, that 

 we can readily understand how not only the educated laity, 

 but the majority of professed naturalists, identified their 

 adherence to the general doctrine with a subscription to the 

 specific principle of natural selection, and in becoming evolu- 

 tionists became at the same time Darwinians, that is to say, 

 natural selectionists. Of late years, however, as conflict has 

 passed from the outworks to the very citadel of evolution, — has 

 come, that is to say, to centre round the problem of the origin 

 of variations, — history has repeated itself. Naturalists such as 

 Nageli, Mivart, and Eimer have championed the cause of 

 internal organismal variations, of evolution in terms of the con- 

 stitution of the organism, of progress according to the definite 



