534 BIOLOGY AND HUMAN LIFE 



development and to reproduce itself. // all the eggs laid by a 

 single house fly in the spring reached maturity, and each female 

 laid her usual number of eggs, and these all developed, and so 

 on through the summer, there would result a mountain of flies 

 as large as a good-sized city. // the eggs of any variety of fish 

 all developed into adults and reproduced in this way for only a 

 few generations, they would fill up the whole ocean. But here 

 are too many conditions that cannot be fulfilled. There is the 

 food supply: What is'the food, and is there enough for all the 

 fly maggots or all the fish fry? There is the presence of ene- 

 mies : Can every egg escape the bacteria and insects and fungi 

 that inhabit the manure heap? Or can every fish egg escape 

 the bacteria and fungi and crustaceans and other fish that 

 swarm in the sea? Putting the situation in another way, it is 

 impossible for all animals to grow up, because growing up itself 

 means the destruction of animals. 



Now the destruction of life is going on all the time, just as 

 the making of new protoplasm is going on all the time; and 

 one process depends upon the other. There is no life without 

 death. The growing body carries on by destroying part of its own 

 protoplasm— the life's energies come from the oxidation of pro- 

 toplasm material ; and the living body grows by obtaining the 

 protoplasm products of other organisms. The result of this 

 relation is the process which has been called the struggle for 

 existence. The idea is that in its struggle to maintain itself life 

 is in perpetual conflict with its surroundings. When the tem- 

 perature gets very low, many seeds or young plants and many 

 eggs or young animals may freeze to death. Here protoplasm 

 struggles to live in a falling temperature. In the woods some 

 plants grow faster than others ; the shaded ones may be unable 

 to get sufficient light to produce all the carbohydrates they 

 need, and they finally perish. Here protoplasm struggles toward 

 the light. Down on the ground, in the shade of the trees, some 

 plants manage to get enough light to live on, while others are 

 shaded to death, just as some seeds manage to survive the cold 

 spell, while others do not. Again, during a period of drought 



I 



