THE ORIGIN OF SPECIES. 43 



"The truth of the principle that the greatest amount of life 

 can be supported by great diversification of structure is seen 

 under many natural circumstances. In an extremely small area, 

 especially if freely open to immigration, and where the contest 

 between individual and individual must be severe, we always 

 find great diversity in its inhabitants. For instance, I found 

 that a piece of turf, three feet by four in size, which had been 

 exposed for many years to exactly the same conditions, sup- 

 ported twenty species of plants, and these belonged to eighteen 

 genera, and to eight orders, which showed how much these 

 plants differed from each other. So it is with the plants and 

 insects on small and uniform islets ; and so in small ponds of 

 fresh water. Farmers find that they can raise most food by a 

 rotation of plants belonging to the most different orders ; Nature 

 follows what may be called a simultaneous rotation. Most of 

 the animals and plants which live close round any small piece of 

 ground could live on it (supposing it not to be in any way pe- 

 culiar in its nature), and may be said to be striving to the utmost 

 to live there ; but it is seen that, where they come into the 

 closest competition with each other, the advantages of diversi- 

 fication of structure, with the accompanying differences of habit 

 and constitution, determine that the inhabitants, which thus 

 jostle each other most closely, shall, as a general rule, belong to 

 what we call different genera and orders." (p. 114.) 



The abundance of some forms, the rarity and final 

 extinction of many others, and the consequent diver- 

 gence of character or increase of difference among the 

 surviving representatives, are other consequences. As 

 favored forms increase, the less favored must dimin- 

 ish in number, for there is not room for all ; and the 

 slightest advantage, at first probably inappreciable to 

 human observation, must decide which shall prevail 

 and which must perish, or be driven to another and 

 for it more favorable locality. 



We cannot do justice to the interesting, chapter 



