Source : Webster's Revised Unabridged Dictionary (1913)

Darwinian \Dar*win"i*an\, a. [From the name of Charles Darwin,
   an English scientist.]
   Pertaining to Darwin; as, the Darwinian theory, a theory of
   the manner and cause of the supposed development of living
   things from certain original forms or elements.

   Note: This theory was put forth by Darwin in 1859 in a work
         entitled ``The Origin of species by Means of Natural
         Selection.'' The author argues that, in the struggle
         for existence, those plants and creatures best fitted
         to the requirements of the situation in which they are
         placed are the ones that will live; in other words,
         that Nature selects those which are to survive. This is
         the theory of natural selection or the survival of the
         fittest. He also argues that natural selection is
         capable of modifying and producing organisms fit for
         their circumstances. See {Development theory}, under
         {Development}.

Darwinian \Dar*win"i*an\, n.
   An advocate of Darwinism.

Source : WordNet®

Darwinian
     adj : of or relating to Charles Darwin's theory of organic
           evolution; "Darwinian theories"
     n : an advocate of Darwinism