I recently read the story "All You Zombies" by Robert A. Heinlein, where time-travel shenanigans by an older version of the main character, out to preserve their own existence, leads to them sleeping with and impregnating their past self... with themselves. Now, disregarding the time travel elements, is it theoretically possible for a human with functioning male AND female reproductive organs, capable of impregnating others as well as becoming pregnant themselves, to exist? How would such a being work? Would it be the result of chimerism, where a sibling absorbs the cells of a sibling while still growing in the womb, or would it need artificial methods to come into being?