Sex anatomy is thought of as occuring in two ways - male orfemale.  This way of separating sex is inaccurate in that evengenetic testing cannot guarantee that you will know what sexcharacteristics a person will have.  Because we have only twocategories of sex, most people are assigned a category at birth and areexpected to stick to that category throughout their lives.

Depending on what hormones affect a fetus during its developement,fetal gonads differentiate into various configuations.  Intersexedpeople's developement didn't settle to one of the extremes of genitaldifferentiation.