404 ELEMENTARY ZOOLOGY 



ence to actual processes or to obvious results, the principles of this 

 chapter. 



The multiplication and crowding of animals. In the 



reproduction or multiplication of animals the production 

 of young proceeds in geometric ratio, that is, it is truly a 

 multiplication. Any species of animal, if its multiplica- 

 tion proceeded unchecked, would sooner or later be 

 sufficiently numerous to populate exclusively the whole 

 world. The elephant is reckoned the slowest breeder of 

 all known animals. It begins breeding when thirty years 

 old and goes on breeding until ninety years old, bringing 

 forth six young in the interval, and surviving until a 

 hundred years old. Thus after about eight hundred years 

 there would be, if all the individuals lived to their normal 

 age limit, 19,000,000 elephants alive descended from the 

 first pair. A few years more of unchecked multiplication 

 of the elephant and every foot of land on the earth would 

 be covered by them. But the rate of multiplication of 

 other animals varies from a little to very much greater 

 than that of the elephant. It has been shown that at the 

 normal rate in increase in English sparrows, if none were 

 to die save of old age, it would take but twenty years to 

 give one sparrow to every square inch in the State of 

 Indiana. The rate of increase of an animal, each pair 

 producing ten pairs annually and each animal living ten 

 years, is shown in the following table: 



Years. Pairs produced. Pairs alive at end of year. 



1 10 II 



2 110 121 



3 1,210 1,331 



4 i3>3!0 14,641 



5 146,410 161,051 

 10 25,937,424,600 



20 700,000,000,000,000,000,000 



