Man in the Light of Evolution 



uals would double in each generation. Frogs 

 produce several hundred eggs at each spawning ; 

 fish, thousands or even millions. The insect lays 

 several hundred eggs. If of all these eggs only 

 two produce mature individuals, the number of 

 the individuals in the species will be maintained. 

 Most species of plants or animals remain about 

 as common or rare one year as another for long 

 periods. 



Sometimes an insect, like the currant worm or 

 potato bug, escapes from a territory where food 

 is limited and enemies abound to a region of 

 fewer enemies and abundant food. It multiplies 

 and swarms, a devastating pest. But animals 

 which feed upon it or parasites which live in it 

 are also benefited. They increase with equal or 

 greater rapidity. Finally they become sufficiently 

 numerous to subdue it or to keep It within 

 bounds. The great and rapid increase has been 

 due to surrounding conditions favoring survival 

 of young, far more than to any increase of repro- 

 ductive power. If all the young of even the 

 most slowly reproducing animals could survive, 

 there would not be standing room for them on 

 the globe after a few centuries. 



Let us suppose that a certain insect produces 



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