My mind was piqued by the idea of endosymbiosis of a bacterium penetrating the cell of an archaean being a precursor to the advent of eukaryotes. And I thought that perhaps something analogous to this sort of thing was also precursor in the advent of metazoa.
For instance, could the first metazoan have been the penetration of an "entrepreneurial" sperm-like choanozoan into the single-celled body of another, genetically similar enough, holozoan? a holozoan, perhaps similar to pluriformea or ichthyosporea? And that choanozoan and other holozoan... those two species found their greatest evolutionary advantage, their quickest ticket to diversification of their descendants, was to work together. To rework their genomes against each other's. And metazoa are actually two holozoan species that intertwined their evolutionary fates with each other's. And their specific genetic distinctivness was sacrificed for the advantages of shuffling their genetic material together. And the success of metazoa is actually the continued reproductive success of those two species. And that subsequent descendant-phyla offload certain functions to one species or the other, resulting in the many diverse levels on the spectrum of sexual dimorphism, that we see throughout non-social species, and also in gender roles as expressed in social animal species. And that conception of a metazoan zygote is the reenactment, eon after eon, of the first joining of those two cells of those two species. The hunting choanozoan swims through an ocean, searching through chemoreception for a cell that has evolved to attract it, enticing it to slam its genetic material into itself. Hunting the waters for something calling to its chemoreceptors. Smelling for a smell familiar enough, a smell that indicates that it is genetically compatible enough, to constitute an invitation. And "maleness" could also actually be thought of as "choanozoa-ness" and "femaleness" could be thought of as the likeness of whatever other holozoan species the first "egg" might have been.
Has anyone heard of any more formal research or speculation into an idea like this?