I have shamelessly poached this topic from a history forum, which posed the question back in 2006 - was Joan of Arc really a man. Now, the thinking behind this was related to a medical condition known as "testicular feminization syndrome" or "complete androgen insensitivity syndrome".
From the website: "The complete androgen insensitivity syndrome is usually detected at puberty when a girl should but does not begin to menstruate. Many of the girls with the syndrome have no pubic or axillary (armpit) hair. They have luxuriant scalp hair without temporal (male-pattern) balding. They are sterile and cannot bear children."
What do we know of Joan that might fall into the above catergory.
1. There was no obvious signs of menstration.
2. She bore no children - child bearing would have been common for a girl of her age - and engaged in no known sexual activity.
3. Despite the saintly modern day depictions, Joan was, by nature of her ancestry, considered to have been short, dark complexioned and swarthy - almost masculine in appearance.
4. Yes she did undergo an "inspection" to ascertain that she was still "virgo intacta" - but would those women who examined her have been at all familiar with a medical condition in which a male took upon, to all intents and purposes, female form. And quite frankly, no man would have undertaken such an intimate examination of a woman.
5. The Duke of Alencon, in his later reflections on Joan, was said to have remarked "... it was if she had known how to be a man-at-armss following the wars since her youth.." And the Burgundian Chronicler Georges Chastellain also commented on her manly skills.
So, just as there is the mystery of Pope Joan - could we have the mystery of John of Arc??