i MENTAL EVOLUTION 3 



tions also occur, and new varieties, if not new species, come 

 into existence at a birth. Further evidence has gone to 

 show that these variations, to which the name of c muta- 

 tions ' has been given, are perpetuated by heredity, while 

 the permanence of the smaller * fluctuations ' has become 

 in some degree matter of doubt. But whether < muta- 

 tions ' or fluctuations ' are the more important in the 

 history of organic evolution is a question which does not 

 affect the validity of the propositions above laid down, 

 nor impair the conclusion drawn from them. Mutations 

 are still variations in individuals qualifying the general 

 resemblance of the parent stock, though they are variations 

 of a different order from that contemplated when individual 

 variations were first conceived as the starting-point of new 

 species. What is still more important, their perpetuation 

 is subject to the conditions of the environment. If the 

 mutation is such as to unfit its possessor to cope with the 

 conditions of life he will not survive to maturity. He 

 will not reproduce his type, and the mutation will dis- 

 appear. If, on the other hand, the mutation is favourable, 

 the stock once gifted with it will multiply and possess the 

 earth. 



In fact the very simple but far-reaching theory which 

 the biologists derived from the still more simple proposi- 

 tions laid down above is not seriously affected by newer 

 views of heredity. Put into its simplest terms the theory 

 merely combines the statements of fact laid down above 

 and draws out the consequences. Variations arise no 

 matter how. We keep to the bare fact. Arising, they 

 are perpetuated again by what mechanism of heredity 

 does not for the moment matter. But they are perpetuated 

 only if they assist, or at lowest do not hinder the individual 

 in the struggle for existence. Hence arises a differen- 

 tiation of type. Of the varying individuals some are 

 weeded out : others survive. From these in turn new 

 variations proceed to meet with the same fate, or rather 

 the same alternatives of fate. Hence by the repeated 

 formation of fresh centres of variation arise the successive 

 growths which constitute new species, new genera, new 

 orders. 



