Thereafter, the development of the internal reproductive organs and the external genitalia is determined by hormones produced by foetal gonads (ovaries or testes) and the cells’ response to them.
The initial appearance of the foetal genitalia (a few weeks after conception) is basically feminine: a pair of “urogenital folds” with a small protuberance in the middle, and the urethra behind the protuberance.
Being intersex is often treated as a medical disorder which should be corrected with treatments such as hormone therapy or surgery to "normalise" sex characteristics.
If an intersex condition is discovered at birth or during childhood then medical procedures may be performed without the child or parent giving consent or even being aware, and many intersex people are not notified of their condition even as adults.
The common habit in the 21st century of elevating the role of the sex chromosomes above all other factors when determining gender may be analogous to the older habit of finding “true” sex in the gonads.
Though school biology lessons teach that men have XY and women XX chromosomes, in fact there are quite a few other possible combinations such as XO, XXX, XXY, XYY, XO/XY, XX male, XY female, and there are many individuals who do not follow the typical patterns (such as cases with four or even more sex chromosomes).
The most common cause of sexual ambiguity is congenital adrenal hyperplasia, an endocrine disorder in which the adrenal glands produce abnormally high levels of virilising hormones.