ORGANIC EVOLUTION 275 



pond a single female frog may lay 300 eggs on a spring 

 morning, and she may repeat the performance in successive 

 years. If half of the succeeding generations were females, 

 and were at maturity equally prolific, and if all should sur- 

 vive to reproduce, a simple calculation would show that in a 

 very few years we should have more bulk of frogs than of 

 water in the pond. Three pairs of oftspring in one hundred 

 years is said to be the rate of reproduction of the African ele- 

 phant—a rate phenomenally slow ; yet even this is an increase 

 of 300% in a century — sufficient if maintained without any 

 losses except from old age, to cover the earth with elephants. 



It is by excess of births that nature provides for inevitable 

 losses; and the excess is proportioned to the dangers to be 

 encountered in the race of life. A single pike may lay 

 upwards of 80,000 eggs each season, scattering them broad- 

 cast in shoal waters, where most of them early fall a prey to 

 other fishes. When hatched, their ranks continue to be 

 thinned, however, in a diminishing ratio, as they become 

 larger and better able to take care of themselves. But if out 

 of all these offspring there remains at maturity for every 

 pair of old pike a single pair of young ones surviving to re- 

 produce each season 80,000 potential offspring, this race of 

 fishes is holding its own; the natural balance is maintained. 

 For more than this proportion to survive persistently would 

 disturb that balance, by depleting the numbers of other 

 fishes on which pike feed. A sunfish that guards its eggs 

 until hatched, need not produce so many of them. But 

 every species, in order to avoid extinction, must produce 

 sufficient excess of off'spring to make good the inevitable loss 

 of life during immaturity, and the failures of adult life. 



Competition. — For want of food, therefore, and often 

 indeed for want of standing room, the vast majority of 

 organisms born into the world are foredoomed to perish 

 before reaching maturity. Yet the method of nature is not 



