1 88 HOLISM AND EVOLUTION chap. 



Darwin assumed two operative factors in the organic 

 world: (i) Variation in the reproduction and inheritance 

 of living beings, and (2) Natural Selection, or the survival 

 of the fittest, as Herbert Spencer called it. Darwin's name 

 is principally associated with the second factor, with which 

 his works mostly deal, and which he elaborated with an 

 unrivalled wealth of detail. He devoted much less attention 

 to Variation, and indeed used it chiefly as a peg on which 

 to hang his theory of the origin of species through Natural 

 Selection. Variation was to him a mysterious fact for 

 Natural Selection to work on. But its spontaneous un- 

 controlled character puzzled him. He found no helpful 

 imagery to explain the puzzle. He suggested the theory 

 of Pangenesis, which showed great insight, but it has not 

 been adopted by his successors. The germ-cell theory, 

 which supplied a mechanism for heredity and variation 

 alike, was a later discovery. The science of Genetics has 

 mainly arisen since his day. Not only were his views on 

 variation meagre and vague, but such views as he had have 

 not been adopted by later Darwinians. Thus in the passage 

 just quoted he attributes variation to the "direct and 

 indirect action of the conditions of life,'' and to "use and 

 disuse." Most Darwinians to-day hold very pronounced 

 views in the opposite direction, and deny that these are the 

 sources of Variation. At present there seem to be indica- 

 tions of a reaction, of a return to Darwin and even to La- 

 marck, and a tendency to look more favourably upon the 

 views of Darwin on this important point. But the fact is 

 that Darwin is on the whole vague on the subject of Varia- 

 tion, and concentrated all his strength on the other principle 

 of Natural Selection and its effects in shaping the organic 

 world. 



However this may be, there is no doubt that both Varia- 

 tion and Natural Selection are essential elements in the 

 Darwinian theory. Darwinism, in fact, implies two factors: 

 an internal factor, operating mysteriously in the inmost 

 nature and constitution of living organisms, and an external 

 factor working along independent lines on the results 



