The Collaborative International Dictionary of English v.0.48:

Polygenesis \Pol`y*gen"e*sis\ (-j[e^]n"[-e]*s[i^]s), Polygeny
\Po*lyg"e*ny\ (p[-o]*l[i^]j"[-e]*n[y^]), n. [Poly- + genesis, or
   root of Gr. gi`gnesqai to be born.] (Biol.)
   The theory that living organisms originate in cells or
   embryos of different kinds, instead of coming from a single
   cell; -- opposed to monogenesis.
   [1913 Webster]