BASIS OF THE PEOBLEM 55 



and I have taken some pains to estimate its probable minimum 

 rate of natural increase ; it will be safest to assume that it begins 

 breeding when thirty years old, and goes on breeding until 

 ninety years old, bringing forth six young in the interval, and 

 surviving till 100 years old ; if this be so, after a period of 740 

 to 750 years there would be nearly ninety million elephants alive, 

 descended from the first pair.' l 



12. These examples show that the power of fecundity, which 

 is always huge, is in many instances much greater than in others. 

 Were it not for the fact that normally all but a small proportion 

 of eggs are always fertilized, it might be suggested that in those 

 cases in which there was no copulation a much larger number of 

 eggs was necessary than among the higher forms, in order that 

 a sufficient number should be fertilized. This, however, can only 

 be a partial explanation of the larger number of eggs among 

 those lower forms where there is no copulation. 



In order to obtain an answer to the question as to what it is 

 which determines the fecundity of any species, it is necessary 

 to look into certain features of the life of animals and plants in 

 a state of nature. Observation and deduction bring one remarkable 

 fact to light. The number of adults of any species at any one 

 season of the year, when compared with the number in the 

 corresponding period in other years, remains upon the whole 

 constant. This fact cannot be based upon statistics, for we cannot 

 take anything approaching to a census. Nevertheless, it is an 

 unavoidable deduction from the known facts. The more emphasis 

 that is laid upon variations in numbers from season to season, 

 the more apparent does it become that such differences are 

 trivial when compared with the possible rate of increase. But we 

 know that all but a small proportion of eggs are fertilized, and as 

 we date the existence of a new member of the species from the 

 moment of fertilization, it is clear that the numbers composing 

 every new generation greatly exceed the number of adults to 

 which the new generation owes its existence. It follows, therefore, 

 that all but a small proportion of the young of each generation 

 perish before the adult stage is reached. The most remarkable 

 increases in the adults of any species ever recorded are negligible 

 compared with the possible increase, and observation shows that 

 as a general rule there is no increase at all. 



1 Darwin, Origin of Species, p. 51. 



