The Collaborative International Dictionary of English v.0.48:

Polygenism \Po*lyg"e*nism\ (p[-o]*l[i^]j"[-e]*n[i^]z'm), n. [Cf.
   F. polyg['e]nisme.] (Biol.)
   The doctrine that animals of the same species have sprung
   from more than one original pair.
   [1913 Webster]