STRUGGLE FOR EXISTENCE 59 



But several seedling mistletoes, growing- close together 

 on the same branch, may more truly be said to struggle 

 with each other. As the mistletoe is disseminated by 

 birds, its existence depends on birds ; and it may meta- 

 phorically be said to struggle with other fruit-bearing 

 plants, in order to tempt birds to devour and thus 

 disseminate its seeds rather than those of other plants. 

 In these several senses, which pass into each other, I 

 use for convenience' sake the general term of struggle 

 for existence. 



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 occa- 

 sional year, otherwise, on the principle of geometrical 

 increase, its numbers would quickly become so in- 

 ordinately 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 a few 

 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 



