variation quotes

I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection, in order to mark its relation to man's power of selection.

- Charles Robert Darwin
  The Origin of Species by Means of Natural Selection, ch.3.

Asto Mr Feeder,B.A.,Doctor Blimber's assistant, he was a kind of human barrel-organ, with a little list of tunes at which he was continually working, over and over again, without any variation.

- CharlesJohn Huffam Dickens
^8  Dombey and Son, ch.11.