tually each returns the very molecules and atoms of its constitution to the air 

 and the waters, and to the earth, from which its substance came. 



It is impossible for every new individual to live out the full cycle typical 

 of his species. A single pair of frogs may produce thousands of eggs in a given 

 season. From a single pair of houseflies starting out in the spring would come 

 enough progeny by the end of the season — // all lived and grew and repro- 

 duced — to fill a space as large as a city block to a height of six or seven stories. 

 Essentially there is the same disproportion between the new admissions and 

 life opportunity for every species — even the slowest growing and the least 

 fertile. 



There is not only a limited amount of space. We may imagine that as 

 species become more differentiated, many will fill in unoccupied spaces and 

 so increase the total amount of living matter in the world. There is, however, 

 a definite limit to the total amount of carbon, hydrdgen, sulfur, nitrogen, 

 phosphorus, and so on. And only a limited fraction of these essential ele- 

 ments can be embodied in living organisms at any time. For plants and ani- 

 mals are "alive" only while the material is actually shifting from the non- 

 living world into the living, from organism to organism, from the organism 

 outward. 



All species are, in fact, closely interrelated through their living processes. 

 Not only do they come into conflict for limited space, light, water, air, the 

 earth elements; but no species could thrive if the others died out, for the 

 various forms of life depend upon one another. Living means dealing with 

 the inanimate world, but it also means dealing with other organisms, directly 

 or indirectly. There is but Httle chance to continue indefinitely the life of 

 individuals; more abundant life seems to be a matter of adjusting the inter- 

 dependent and the conflicting elements for a balanced total. This balance 

 among all living things is itself a constant rise and fall, a constant coming and 

 going, a constant give and take. Like the waves of the sea, which endlessly 

 take on similar shapes and yet are never for two moments the same, life is a 

 continuous balancing and adjusting rather than a crystallized and finished 

 fact. 



526 



