376 CHARLES ROBERT DARWIN. 



fruit, and by care in animal life the swiftest horses 

 for speed as well as the strongest for labor, so 

 nature selects her best for the higher development 

 of the race. 



Darwin says, " There is no exception to the rule 

 that every organic 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 literally not be standing-room 

 for his progeny. . . . The elephant is reckoned 

 the slowest breeder of all known animals ; it will 

 be safest to assume that it begins 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." 



In various ways the weakest are destroyed. 

 Darwin, on a piece of ground three feet long and 

 two wide, says, " I marked all the seedlings of our 

 native weeds as they came up, and, out of 357, no 

 less than 295 were destroyed, chiefly by slugs and 

 insects." 



He gives this interesting instance of the strug- 

 gle for existence. "I find from experiments that 

 humble-bees are almost indispensable to the fertil- 

 ization of the heart's-ease, for other bees do not 

 visit this flower. . . . Humble-bees alone visit red 



