4 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



in almost any 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 infinite complexity of the rela- 

 tions of all organic beings to each other and to their 

 conditions of life, causing an infinite diversity of struc- 

 ture, constitution, and habits, to be advantageous to 

 them, it would be a most extraordinary fact if no varia- 

 tions had ever occurred useful to each being's own wel- 

 fare, 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 off- 

 spring similarly characterized. This principle of pre- 

 servation, or the survival of the fittest, I have called 

 natural selection. It leads to the improvement of each 

 creature in relation to its organic and inorganic condi- 

 tions of life ; and consequently in most cases, to what 

 must be regarded as an advance in organization. 

 Nevertheless, low and simple forms will long endure 

 if well fitted for their simple conditions of life." 



It is readily perceived that this statement makes 

 no attempt to account for the origin of variations, but 

 that it simply formulates, as observed by Mr. Darwin, 

 the doctrine of survival of such variations as are most 

 useful to their possessors. This fact is more distinctly 

 pointed out in the same work (p. 63) where the author 

 remarks: "Several writers have misapprehended or 

 objected to the term natural selection. Some have 

 even imagined that natural selection induces variabil- 

 ity, whereas it implies only the preservation of such 



