You sound like you know more about this than I do. Are there any theories (not even with evidence) about how sex evolved? I can’t find a way two unrelated species (that did not have a “mother and father” of some sort) came together to produce the first ever offspring with two progenitors. In otherwords some creature was conceived (using the term lossely) and born in a way vastly different from it’s parent. All the “plumbing” (organs) needed for that first combination, which would have been an evolutionary anchor up to that point, is something I can’t see my way around.