LECTURE XXII. 



THE STRUGGLE FOR EXISTENCE. 



No one doubts it ; no one realizes it. More born than 

 mature ; all live who can ; all destroyed who cannot 

 meet the conditions ; the killing never indiscriminate. 



Law of Malthus (Thomas Malthus, 1798 : " Prin- 

 ciples of Population"). Man tends to increase in 

 geometric ratio ; food supply in arithmetical ratio. 

 Criticisms of this law as a partial truth. Darwin's 

 application of this law to animals and plants. Any 

 rate of increase in a limited world leads to a struggle 

 for existence. Ratio of increase of minor importance, 

 for all geometric progressions in time outrun all arith- 

 metical progressions. Those increase who do not live 

 ki beyond their income," the rest perish. 



Herschel's observation on man. Not hard matter 

 enough in the earth for the bones of the men that 

 might theoretically be alive. 



Increase of protozoa. Bacteria would fill sea in a 

 month. Rate of increase of codfishes ; of sparrows ; 

 of elephants ; of man ; of flies. " Three flies will de- 

 vour a dead horse as quickly as a lion."- Linnseus. 

 One hundred trillion flies in the world today ; in three 

 months one pair would produce as many. Should 

 each fly have the most favorable environment no one 

 could escape the plague of flies. Ten million birds in 

 England ; fifty million birds and birds' eggs die every 

 year, and of this destruction no traces seen. 



