GEOMETRICAL RATIO OF INCREASE 79 



birds to devour and thus disseminate its seeds. In these sev- 

 eral senses, which pass into each other, I use for conveni- 

 ence sake the general term of Struggle for Existence. 



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, other- 

 wise, on the principle of geometrical 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 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 increas- 

 ing, 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. Lin- 

 naeus 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 ele- 

 phant is reckoned the slowest breeder of all known animals, 

 and I have taken some pains to estimate its probable mini- 

 mum rate of natural increase ; 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 



