maybe we could self reproduce before. maybe a mad scientist in atlantis separated our x and y chromoses and genetically sepated males from females and created a division of the sexes. maybe we used to have both the x and y sequence and could both reproduce offspring, the hyleg of the x in males is now a y, so males are dependant on females with the x sequence for gestation, maybe males used to have an x and females had an xy or other self reproducing combination. geneticists are not telling us the whole story of our chromosomes and thier functions and capacities. or maybe we just de-evolved from a rough life on terra firma and now need sex , cross pollination.