If you pass Norrie on the sidewalk, you won't be able to tell if she is a man or a woman.
The 49-year-old walks through her gritty Sydney, Australia neighborhood barefoot and wearing a dress. She is flat-chested, has an Adam's Apple, medium-sized feet and sports a haircut that could be male or female -- short in the back and on the sides, with a mop of long hair on top. She wears little or no make-up.
Norrie goes by only one name and is a self-described 'spansexual.' She was the first person in the world ever to be issued identity papers that state: "Sex Not Specified."
"I see myself as male and female," she said. Norrie is happy to be referred to as "he" or "she" in conversation. But says she doesn't want her identity documents to be telling lies.
"In terms of M or F," Norrie said. "I'm not specifically M or F. You can't specify me as being male or you can't specify me as being female without committing a 'fudge' at the very least."
Two doctors examined Norrie and couldn't determine that she was one sex or the other, physically or psychologically. So the State of New South Wales issued her a document that states: "Sex Not Specified."
"There are men, women -- most of us fall into one of those categories," said Professor Walter Bockting from the University of Minnesota Medical School, who has been researching gender identity development. "But then there is a minority who falls in between."
Norrie was born, anatomically, as a normal boy in a small Scottish town. Her family immigrated to Australia when she was seven, where she grew from an awkward adolescent into a glamorous gay man.
"At that stage, I was very androgynous," Norrie said. "That was the 1980s when Boy George was allowed to do it, but don't you do it in real life!"
Norrie said that during the day, she was discriminated against at her job in a government office for her appearance and sexual orientation. At night, Norrie socialized with transvestites and transsexuals where she felt accepted.
Eventually, she started dressing in drag and came to believe she was a woman trapped in a man's body.
"I knew that I couldn't do the role of man," she explained. "The role of woman seemed to be one I was getting approval for and felt natural for me."
At the age of 27, Norrie had sex change surgery to remove her penis and testicles and to create a vagina. She said the first couple of years after her surgery were liberating.
"I was absolutely ecstatic about it," she said. "Until I got involved with straight guys who, when they found out I was a 'trannie,' told me I wasn't a female. They felt they'd been lied to. I was threatened with violence."
Norrie explained that she then began to question gender itself, the simple male/female dichotomy. It's a question that Professor Bockting has been researching for the past 25 years.
"Historically, there have always been transgender people," he said. "There were cultures where there were more than two genders."
Bockting explained that some Native American tribes had a third gender: The "berdache" or men who lived as women. To this day, a third gender is socially accepted in Thailand: the "Kathoey," or lady boys. Across South Asia, the Hijra, most of whom are born outwardly male, have surgery and choose to live like women, remain an important, mystical part of Hindu culture.