NATURAL SELECTION 49 



study of the nature of individual differences and of 

 other kinds of variations, as well as of the manner of 

 operation of ' the strong principle of inheritance,' has 

 confirmed this view as to the method of origin of 

 species, or has led to the introduction of modifications. 



Let it be remembered that this suggestion of a 

 natural means of modification had, within a few years, 

 the effect of convincing practically the whole thinking 

 world of the truth of the theory of organic evolution 

 an effect which all the other arguments recited in the 

 last chapter were quite unable to produce, so strong 

 was the then existing prejudice in favour of the doc- 

 trine of special creation. 



The truth of the general principle of the survival of 

 the fittest is quite untouched by recent criticism ; 

 but a great deal of argument has been expended over 

 the questions : (i) how much fitness is sufficient to 

 lead to survival j and (2) whether very small advan- 

 tages in the way of fitness, even if they lead to the sur- 

 vival of the individuals which exhibit them, will be 

 followed to an indefinite extent in succeeding genera- 

 tions by further improvements in the same direction. 

 We shall find that a good deal of evidence has accu- 

 mulated tending to show that the second of these 

 questions must be answered in the negative, although 

 the point is not yet settled to the satisfaction of 

 everyone. The remainder of the present chapter will 

 be occupied in discussing some of the arguments which 

 bear upon this question. 



An important factor which must probably be added 

 to the factors of variation, selection, and heredity, in 



4 



