Oh, Dark. More info:

There are many different reasons a person may exhibit a mix between male and female genitalia. In many cases, the individual has a "normal" genotype (XX or XY) but a mutation in some other gene that causes the genitalia to form differently. It is important to realize that every human being starts out as a "hermaphrodite," in that you possess both male and female proto-sexual organs while you are developing, and one or the other is typically suppressed/degrades depending on your chromosomal makeup.

The most common intersex condition is congenital adrenal hyperplasia, where a person's adrenal glands produce higher than normal masculanising hormone levels, resulting in the partial to complete masculanisation of the genitalia of an XX individual.