The Collaborative International Dictionary of English v.0.48:

Evolutionist \Ev`o*lu"tion*ist\, n.
   1. One skilled in evolutions.
      [1913 Webster]

   2. One who holds the doctrine of evolution, either in biology
      or in metaphysics. --Darwin.
      [1913 Webster]

WordNet (r) 3.0 (2006):

evolutionist
    n 1: a person who believes in organic evolution