Sex reversal is the process that changes the sexual identity of an individual from one sex to the other, often through a combination of surgical, pharmacologic, and psychiatric procedures is called a sex reversal. We can observed the complete sex reversal in birds (unlike man) if the hormones are injected in the embryo at very early stage of development.
In mammals also, if the gonads are removed at an early stage (the process is called castration or ovariectomy) or they got destructed by some disease, it results in an intersex appearance due to partial or complete reversal of secondary sexual characters. In Middle East, North Africa and China, boys are castrated before puberty called eunuchs, which were employed as harem chamberlains. The process of castration is useful in animal husbandry in order to increase fat content and improve the quality of meat by avoiding undesirable odors from the meat of adult males. It also helps in taming animals like oxen which are used for carrying loads.
By means of plastic surgery and the hormonal treatment, a human intersex may opt for a sex reversal process but, however, they remain sterile.