The majority are the result of something going wrong early in a pregnancy, where the fetus is exposed to an inappropriate amount of hormones in the uterus.

You can get genetic girls who look from the outside like males because they were exposed to male hormones at a critical stage of fetal development. Conversely, you can get genetic males looking like females because they didn't get enough male hormones in utero.

There are a whole group of more mixed external manifestations of gender that also occur.

Until the 1950's, when an intersex child was born, they were let be. But starting in the 1950's, the general approach was to make the child into one sex or another. If it was a partially masculinized female, there was a surgical attempt to turn her into a "normal" female. Structures were created so that she could have intercourse later.

If the child was a genetic male, the question was, Will the adult penis be large enough for sexual intercourse? The vast majority of the children with severe inadequacy of the penis were converted to "female" surgically and then raised as girls.

Q. So the prescription for the intersex boys was castrate them and put them into a dress?

A. The problem was, In a large number of children, as with my first intersex patient, it never took. Gender has far more to do with other important structures than external genitals.

Q. How do you know what constitutes gender identity?

A. As part of a research study, I've personally seen and assessed 400 children with major anomalies of the genitals. Of those, approximately 100 might be called "intersex." Our findings have been many and complex. The most important is that about 60 percent of the genetic male children raised as female have retransitioned into males.

We also found that of this group there were some genetically male children, who despite genital anomalies were raised as males, and they continued to declare themselves as male.