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Basically, if we resorted to programming analogies which everyone understands here - you have a program with a bug and you try these approaches:
* you shuffle the program code randomly, compile and test millions of times until the bug is fixed - this is mutation breeding
* you sit back and wait for a random bit flip in the code to bring you closer to the bugfix - this is selection breeding
* you debug program, find the bug and fix it using vim - this is CRISPR