"It cannot but happen?that those will survive whose functions happen to be most nearly in equilibrium with the modified aggregate of external forces? This survival of the fittest implies multiplication of the fittest."

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But you must not change one thing, one pebble, one grain of sand, until you know what good and evil will follow on that act. The world is in balance, in Equilibrium. A wizard's power of Changing and Summoning can shake the balance of the world. It is dangerous, that power...It must follow knowledge, and serve need.

— Ursula K. Le Guin