DARWIN^ BEFORE AND AFTER 107 



important part in the oripn of species. The same spot 

 will support more life if occupied h\ very diverse forms. 

 We see this in the many generic forms in a square yard 

 of turf, and in the plants or insects on any little uniform 

 islet, belonging almost invariably to as many genera and 



families as species Now, every organic being, by 



propagating so rapidly, may be said to be striving its 

 utmost to increase in numbers. So it will be with the 

 offspring of any species after it has become diversified . 

 into varieties, or subspecies, or true species. And it 

 follows, I think, from the foregoing facts, that the vary- 

 ing offspring of each species will try (only few will suc- 

 ceed) to seize on as many and as diverse places in the 

 economy of nature as possible. Each new variety or 

 species, when formed, will generally take the place of, 

 and thus exterminate its less well-fitted parent. This T 

 believe to be the origin of the classification and affinities 

 of organic beings at all times, for organic beings always 

 seem to branch and sub-branch like the limbs of a tree 

 from a common trunk, the flourishing and diverging 

 twigs destroying the less vigorous — the dead and lost 

 branches rudely representing extinct genera and 

 families." 



Again, in 1872, Darwin stated : " If under changing 

 conditions of life organic beings present individual dif- 

 ferences in almost every part of their structure, and this 

 cannot be disputed ; if there be, owing to their geometric- 

 al 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, consti- 

 tution, 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 



