I can't reply to your response to my comment because of the screening thing.

What seemed improbable? The whole concept of how babies were made. If there was a specific action that made babies, then there wouldn't be people who wanted babies and didn't have them, and there wouldn't be people who didn't want them who did have them. Obviously, getting pregnant was like getting a cold: a sort of contagion from sleeping together, and you might be lucky or unlucky.

I don't know how I ever came to believe the truth. Probably found it in a book somewhere, eventually.