Chap. HI.] GEOMETKICAL EATIO OF INCEEASE. 79 



Geometrical Ratio of Increase. 



A struggle for existence inevitably follows from the 

 high rate at which all organic beings tend to increase. 

 Every being, which during its natural lifetime produces 

 several eggs or seeds, must suffer destruction during 

 some period of its life, and during some season or 

 occasional year, otherwise, on the principle of geometri- 

 cal increase, its numbers would quickly become so 

 inordinately great that no country could support the 

 product. Hence, as more individuals 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, or with the physical conditions 

 of life. It is the doctrine of Malthus applied 

 with manifold force to the whole animal and 

 vegetable kingdoms ; for in this case there can be no 

 artificial increase of food, and no prudential restraint 

 from marriage. Although some species may be now 

 increasing, more or less rapidly, in numbers, all cannot 

 do so, for the world would not hold them. 



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. Linnseus 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 million plants. The 



