48 THE THEORY OF NATURAL SELECTION 



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 

 infinite complexity of the relations of all organic 

 beings to each other and to their conditions of life, 

 causing an infinite diversity in structure, constitu- 

 tion, and habits, to be advantageous to them, it would 

 be a most extraordinary 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 charac- 

 terized. This principle of preservation, 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 conditions of life, and, conse- 

 quently, in most cases, to what must be regarded as an 

 advance in organisation. Nevertheless, low and 

 simple forms will long endure, if well fitted for their 

 simple conditions of life.'* 



We have here a very definite and concise statement 

 of the way in which Darwin believed the principle of 

 natural selection to take effect in the production of new 

 kinds of organisms. It will be our business in this and 

 in succeeding chapters to show how far the modern 

 * ' Origin of Species,' sixth edition, p. 96. 



