192 HOLISM AND EVOLUTION chap. 



The alterations in the Darwinian scheme introduced by 

 Darwin's successors have had a profound effect on that 

 scheme as a whole; so much so that it is to-day difficult to 

 say how much of Darwin's great vision still survives. In 

 order to realise this, it would be advisable to compare Dar- 

 win's general ideas of the facts of Variation with the modi- 

 fications introduced by his successors. 



In Darwin's view, it was not only the operation of Natu- 

 ral Selection that was moulding living things in conformity 

 with their environment, by eliminating those that were less 

 suited to the conditions of the environment. Variation 

 was also bearing its share in this process of assimilating 

 and adapting them to the environment. The close fitting 

 of species to their habitats and environmental conditions 

 which is so distinctive of animate Nature was, according 

 to him, the combined effect both of Natural Selection and 

 Variation. 



In order to ensure clearness in what follows we have to 

 distinguish between various forms of so-called ''variation" 

 in living things. In the first place, we have modifications, 

 which are due to the functional activities and experiences 

 of the individual in its own life, and not to inheritance from 

 parents or ancestors. The effects on the bodily organism 

 or on particular organs of their use or disuse in any definite 

 way would be such modifications. An animal changes its 

 mode of life and in consequence ceases to use certain organs, 

 or begins to use them in a new way or for a new purpose. 

 Such disuse tends to the atrophy of these organs, just as 

 such new or increased use would develop them. Such 

 atrophy or development respectively in the bodily organism 

 is a modification. All changes or characteristics acquired 

 during the individual life are modifications. 



In the second place we have variations, which are small 

 changes passing by inheritance, and not due to the develop- 

 ments or acquisitions of the individual life. A small altera- 

 tion from the type which an animal has inherited from its 

 parents is a variation, in contradistinction to a modification 

 which has been brought about in its own Hfetime. In the 



