oneness of origin; esp. (biol.), development of all beings in the universe from a single cell; -- opposed to polygenesis. called also monism.-that form of reproduction which requires but one parent, as in reproduction by fission or in the formation of buds, etc., which drop off and form new individuals; asexual reproduction.-the direct development of an embryo, without metamorphosis, into an organism similar to the parent organism; -- opposed to metagenesis.