All You Zombies

I was just reading a book for Astro and I came across an exceedingly interesting story written in 1959 by Robert Heinlein. I shall relate it here as it appears in J. Richard Gott's book "Time Travel in Einstein's Universe (2001):

"A 25-year old man is in a bar lamenting his fate, curiously he calls himself the "Unmarried Mother." He tells the bartender his story. This man has had it rough. He had been born a girl and raised in an orphanage. As a young woman, she had had sex with a man who then abandoned her. She became pregnant and decided to keep the baby. When it came time to give birth, she had a cesarean section. The baby was born - it was a girl. During the operation, the doctor noticed that the woman had, hidden inside her body, male as well as female organs. With some reconstructive surgery, the doctor transformed her into a man without her consent. This is why the man refers to himself as the "Unmarried Mother." Moreover, the child was soon kidnapped from the hospital by a stranger.

The bartender interrupts the young man's story: "The matron at your orphanage was Mrs. Fetherbridge - right? ... Your name as a girl was Jane - right? And you didn't tell me any of this - right?" The bartender asks the Unmarried Mother whether he wants to find the man who had gotten "him" pregnant. He does. Then the bartender ushers the unfortunate young man to the rear of the bar to a time machine. They go back in time 7 years and 9 months, where the bartender drops the man off. The bartender goes forward in time 9 months just in time to abduct a baby named Jane. He next takes baby Jane back 18 years earlier in time and puts her on the steps of an orphanage. After that he returns to the young man, who has just impregnated a young woman named Jane. The bartender then takes the young man to the future to learn the trade of bartending. At the end, the bartender considers the whole affair, and looks down at his old cesarean scar: "I know where I come from - but where did all you Zombies come from?" he muses."