"Dual-Gender" among humans is a mutation not only caused by pollution or radiation, it is also caused by severely damaged chromosomes, i seen a documentary movie about it on Discovery Science some time ago.
While being an "unwanted" mutation seen by human scientists and common folk, some believe it is actually nature's stance on human evolution. The fact that there are so few of living specimens of both gender humans (altered surgically to be a single gender or otherwise hiding) means that nature itself is taking an option into consideration, whether it's accepted by humans or not, if nature itself will decide this is the course we should go, we have little to say about it 20.000 years in the future.
But the basic idea is, XX chromosome is defining a human Female right now, any other change is resulting in subject not being a female.
I see the question I stated earlier gives as much problem to answer as I expected it to be, however in many groups I tried that, I get different areas of answers, here on forums we met on genetic area, when at work, I landed on different language notions and their dictionary explanations. I found those boring explanations which make me question the logical ability of my co-workers, here at least I can have an interesting discussion on the field.
