NATURAL SELECTION 185 



recently shown that in the S.E. corner of Australia, 

 where, apparently, there are many invaders from different 

 quarters of the globe, the endemic Australian species 

 have been greatly reduced in number. How much weight 

 to attribute to these several considerations 1 will not 

 pretend to say; but conjointly they must limit in each 

 country the tendency to an indefinite augmentation of 

 specific forms. 



Summary of Chapter 



If under changing conditions of life organic beings 

 present individual differences in almost every part of 

 their structure, and this cannot be disputed; if there be, 

 owing to their geometrical rate of increase, a severe 

 struggle for life at some age, season, or year, and this 

 certainly cannot be disputed; then, considering the in- 

 finite complexity of the relations of all organic beings 

 to each other and to their conditions of life, causing an 

 infinite diversity in structure, constitution, and habits, to 

 be advantageous to them, it would be a most extraordi- 

 nary fact if no variations had ever occurred useful to 

 each being's own welfare, in the same manner as so 

 many variations have occurred useful to man. But if 

 variations useful to any organic being ever do occur, 

 assuredly individuals thus characterized will have the 

 best chance of being preserved in the struggle for life; 

 and from the strong principle of inheritance, these will 

 tend to produce offspring similarly characterized. This 

 principle of preservation, or the survival of the fittest, I 

 have called Natural Selection. It leads to the improve- 

 ment of each creature in relation to its organic and inor- 

 ganic conditions of life; and consequently, in most cases, 



