sym·bi·o·gen·e·sis 
(sĭm′bē-ō-jĕnĭ-sĭs, -bī-)
(sĭm′bē-ō-jĕnĭ-sĭs, -bī-)n.
The formation of a new organism through the merging of two or more free-living organisms. Some biologists believe that symbiogenesis is an important mechanism of evolutionary change.
sym′bi·o·ge·netic (-jĕ-nĕtĭk) adj.