Chap. III.] GEOMETRICAL RATIO OP INCREASE. 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 oc- 

 casional year, otherwise, on the principle of geometri- 

 cal increase, its numbers would quickly become so in- 

 ordinately great that no country could support the pro- 

 duct. Hence, as more individuals are produced than 

 can possibly survive, there must in every case bea~ 

 struggle for existence, either one individual with an- 

 other 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 rapid- 

 ly> 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. 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 should be a million plants. The 



