The Collaborative International Dictionary of English v.0.48:

Evolutionism \Ev`o*lu"tion*ism\, n.
   The theory of, or belief in, evolution. See Evolution, 6
   and 7.
   [1913 Webster]

WordNet (r) 3.0 (2006):

evolutionism
    n 1: (biology) a scientific theory of the origin of species of
         plants and animals [syn: theory of evolution, theory of
         organic evolution, evolutionism]