82 DARWINISM AND HUMAN LIFE 



would, at the end of sximmer, weigh down the 

 population of China. 



The common house-fly lays eggs in batches of 

 120 to 150 at a time, and may lay five or six of 

 these batches during its life — of about three weeks 

 in very hot weather. At the end of summer, if all 

 developed, and if there were six generations, the 

 progeny of a single pair, pressed together into a 

 solid mass, would occupy a space of something like 

 a quarter of a million cubic feet, allowing 200,000 

 flies to a cubit foot. There is no real increase, 

 hence the mortality must be prodigious. 



The intensity of the struggle can be inferred 

 from the rate of increase. If there is slow multi- 

 pUcation and yet no falling ofiE in the number of 

 adults, there is no keen struggle for existence. If 

 there is rapid multiplication and yet no increase 

 in the number of adults, there must be a keen 

 struggle for existence. It is useful to think over 

 the simple equation : the number produced minus 

 the number eliminated equals the normal number 

 of adults. 



(b) Another reason follows from the pattern of 

 the web of life — there are nutritive chains, one 

 organism depending on another for its food-supply. 

 Indeed, the struggle that strikes us most is that 

 which follows from the obvious fact that many 

 animals prefer to be carnivorous. There is a good 

 deal of the conjugation of the verb " To eat " in 

 life, and the objection to be eaten is as natural 

 to some animals as the desire to eat is to others. 



(c) A third reason for struggle is to be found 

 in the irregular changefulness of the physical 

 environment. Give an animal time, and it may 

 become marvellously well adapted to its surround- 



