The Evolution 



of Communities 



The millions of species of plants and animals that 

 evolved formed the species mixtures constituting 

 the biological communities of the world. These com- 

 munities, however, are not random mixtures of 

 species. The species living together today exhibit 

 various degrees of adjustment to each other as well 

 as to their physical habitat. Some of these inter- 

 specific adjustments are so intimate that they can 

 be no happenstance but must have come about by 

 a process of evolution. The conclusion seems obvious 

 that, first of all, species mixtures occurred, then 

 some sort of order evolved within these mixtures. 

 Questions relevant to this situation are: How did 

 the first species mixtures occur, how many species 

 had to occur in a mixture before some sort of order 

 evolved, what kind of order evolved first, and what 

 influences were involved? The first prerequisite to 

 investigating these questions is an understanding of 



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