86 THE EVOLUTION OF ANIMALS. 



organic evolution becomes a theory of the causes and condi- 

 tions which lead to isolation " (Romanes). 



Cumulative Effect of Definite Variations. 



According to some other naturalists (Buffon, Lamarck, Tre- 

 viranus, Erasmus Darwin, Mivart, Cope, Eimer, and Geddes), 

 definite variations due to the sustained action of the en- 

 vironment, or to persistent change of function, or to internal 

 conditions of growth, may accumulate in the course of 

 generations, so that new, well-adapted, and progressive 

 species are evolved. 



In regard to environmental and functional variations, how- 

 ever, it is at present difficult to decide as to the degree in 

 which they are transmissible. 



Struggle for Existence. 



Geddes especially has protested against exaggerating the 

 importance of the individual struggle for existence, main- 

 taining that some of the most important steps in evolution 

 have been due to the subordination of nutritive to reproduc- 

 tive activities, of self-preserving to species-maintaining func- 

 tions, of egoism to altruism. Kropotkin has also shown 

 with much carefulness that mutual aid is exhibited by many 

 animals, and that it modifies and ennobles the struggle for 

 material subsistence. 



It should be remembered that Darwin intended the 

 phrase " struggle for existence " to be used " in a wide and 

 metaphorical sense." He did not mean it to be restricted 

 to individualistic competition for food. He meant it to 

 include all endeavours for the well-being both of the indi- 

 vidual and the offspring. 



Moreover, as natural selection simply means that useful- 

 variations succeed and that the unfit are eliminated, it 

 justifies altruistic endeavour no less — in some cases more — 

 than egoistic struggle. 



It seems to me quite possible to combine all the theories 

 of evolution : the difficulty is to know in what proportions. 



Meanwhile I suggest the following balance-sheet of 

 opinions : — 



