1468 THE STORY OF THE UNIVERSE 



viduals are produced than can possibly survive, there 

 must in every case be a struggle for existence, either 

 one individual with another of the same species, or 

 with the individuals of distinct species. 



There is no exception to the rule that every or- 

 ganic being naturally increases at so high a rate that, 

 if not destroyed, the earth would soon be covered 

 by the progeny of a single pair. Even slow-breeding 

 man has doubled in twenty-five years, and at this 

 rate, in less than a thousand years, there would liter- 

 ally not be standing-room for his progeny. Linnaeus 

 has calculated that if an annual plant produced only 

 two seeds and there is no plant so unproductive as 

 this and their seedlings next year produced two, 

 and so on, then in twenty years there would be a mil- 

 lion plants. The elephant is reckoned the slowest 

 breeder of all known animals, and I have taken some 

 pains to estimate its probable minimum rate of nat- 

 ural increase; it will be safest to assume that it be- 

 gins breeding when thirty years old, and goes on 

 breeding till ninety years old, bringing forth six 

 young in the interval, and surviving till one hundred 

 years old; if this be so, after a period of from 740 

 to 750 years there would be nearly nineteen million 

 elephants alive, descended from the first pair. 



But we have better evidence on this subject than 

 mere theoretical calculations; namely, the numerous 

 recorded cases of the astonishingly rapid increase of 

 various animals in a state of nature, when circum- 

 stances have been favorable to them during two or 

 three following seasons. Still more striking is the 

 evidence from our domestic animals of many kinds 



