Technically you're not wrong, when the first mother of gender decided to evolve gender from lesser components, she had both a penis and a vagina, one for spraying acid swimmers at the enemy who tore chunks off the enemy hull land brought it back as calories, the best of which were vacuumed up by the vagina and the best one rewarded with repetitive production as I make more immune system fluid. So there she was, spraying immune system and vacuuming up those that return with food after wrecking enemy, and a disaster happened during mitosis, the mouth and penis went one way, and the mouth and vagina went the other way, amazingly, somehow, defying belief, it all worked, and not only that, it worked better.

Now you are this disaster that found a local maximum in dominating a planetary surface.