The Atlantic Monthly, Volume 18, No. 108, October, 1866, page 69 by Various Authors
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ecome feral; and this would certainly greatly alter (as indeed I have observed in parts of South America) the vegetation: this, again, would largely affect the insects; and this, as we just have seen in Staffordshire, the insectivorous birds, and so onwards in ever-increasing circles of complexity."
In the struggle for life, the strongest live; or, in other words, those best fitted to live in the environment endure. Animals and plants produce in vast excess of the possibility of life. A destruction of life is going on to an almost incredible amount. Were this not the case, the slowest breeders in existence would soon cover the earth so as to occupy every inch of space. Darwin reckons that the elephant, the slowest breeder, if allowed to go on unchecked, and to live his allotted term of years, would in five centuries produce fifteen millions of elephants from one pair. If every cod's egg had developed into a full-grown fish, the whole ocean would, ages ago, have been packed with them, like herrings in a box. In this destruction, the weaker animals and plants--those least fitted to thrive under the influences around--become the prey of others better fitted for the struggle, or die of their own lack of assimilative force. Thus, through untold ages of shifting outward circumstances, the plastic forms of organic life have been remoulded. A little obscure plant, the food of an insect, dies out; the insect itself, deprived of its food, dies out or migrates; the bird which fed upon it dies out or migrates; the bird of prey follows the like course. Migration introduces them to an entirely new state of existence, temperature, food, and antagonists. The migrating animals are replaced by others, which likewise experience new surroundings; and thus the extirpation of a single plant may determine a long series of changes. Instances of this kind are not uncommon. What must these changes have been throughout the remote ages which have turned sea-shore mud into uplifted mountain chains, and sunk long-stretching, sunny hill