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FACTORS OF EVOLUTION.
An organism, as living matter, does not stand in opposition to, or outside of, the rest of the world. It is part of the world. It receives matter from its surroundings, and gives some back; therefore it is influenced by its surroundings. It is acted upon, and it reacts upon the latter, and if these change (and they are nowhere and never strictly the same) the organism also varies. It adapts itself, and if it does not, or, rather, cannot, do so, it dies, because it is unfit to live in the world, or, rather, in those particular surroundings and conditions in which it happens to be. That organism which yields most easily, accommodates itself most quickly, has the best chance of existence—survival of the fittest.
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