[4] The fitness requirements for androdioecy to arise and sustain itself are theoretically so improbable that it was long considered that such systems do not exist.
This means that all else being equal, males have to fertilize twice as many eggs or ovules as hermaphrodites to make up for the lack of female reproduction.
[9] In the well-studied roundworm Caenorhabditis elegans, males are very rare and only occur in populations that are in bad condition or stressed.
[citation needed] The most common form of androdioecy in animals involves hermaphrodites that can reproduce by autogamy or allogamy through ovum with males.
[12]: 21 Another type of androdioecy has males and simultaneous hermaphrodites in a population due to developmental or conditional sex allocation.