This is what I love about this website: We can start talking about the mental agility of those who write books, but then wind up talking about gender distribution in the medical profession.
I first heard that riddle in the 70s (during the heyday of the women's lib movement) and it was designed to call us out for being an inherently sexist society. I think it did that superbly. We were supposed to think - oh yeah...women can be surgeons too...ain't I a sexist bastard! Anyway a woman doctor is just not all that usual today. In fact, I think I read somewhere that more women than men graduated from medical schools in the United States last year. I am willing to bet, though, that surgery is still predominately a male sport.
So here's what I like about your post, Vota. It calls me out for my own prejudices. I have always considered father-and-son to be a blood relationship. Father and son, or for that matter, mother and son, share 50% of the same DNA. To my mind a step dad is a legal construct - related by a marriage contract, and you can change who you're married to, but you can't change your blood. That is in no way meant to diminish the bonds of affection between a step dad and his step son.