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beings and to external nature, will tend to the preservation of that individual, 

 and will generally be inherited by its offspring. The offspring, also, will thus 

 have a better chance of surviving, foi*, of the many individuals of any species 

 which are periodically born, but a small number can survive. 



" This 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 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 another of the same species, or with 

 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. 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 elephant 

 is reckoned the slowest breeder of all known animals, and I have taken 

 some pains to estimate its probable minimum rate of natural increase ; it 

 will be under the mark to assume that it breeds when thirty years old, and 

 goes on breeding till ninety years old, bringing forth three pair of young in 

 this interval ; if this be so, at the end of the fifth century there would be alive 

 fifteen millions of elephants, descended from the first pair. 



" But we have better evidence on this subject than mere theoretical 

 calculations, namely, the numerous recorded cases of the astonishingly rapid 

 increase of various animals in a state of nature, when circumstances have been 

 favourable to them during two or three following seasons. Still more striking 

 is the evidence from our domestic animals of many kinds which have run wild 

 in several parts of the world ; if the statements of the rate of increase of slow 

 breeding cattle and horses in South America, and latterly in Australia, had 

 not been well authenticated, they would have been incredible. So it is with 

 plants : cases could be given of introduced plants which have become common 

 throughout whole islands in a period of less than ten years. Several of the 

 plants, such as the cardoon and a tall thistle, now most numerous over the 

 wide plains of La Plata, clothing square leagues of surface almost to the 

 exclusion of all other plants, have been introduced from Europe ; and there are 

 plants which now range in India, as I hear from Dr. Falconer, from Cape Comorin 

 to the Himalaya, which have been imported from America since its discovery. 

 In such cases, and endless instances could be given, no one supposes that the 

 fertility of these animals or plants has been suddenly and temporarily increased 

 in any sensible degree. The obvious explanation is that the conditions of life 

 have been very favourable, and thei-e has consequently been less destruction of 

 the old and young, and that nearly all the young have been enabled to breed. 

 In such cases the geometrical ratio of increase, the result of which never fails 

 to be surprising, simply explains the extraordinarily rapid increase and wide 

 diffusion of naturalized productions in their new homes. 



