Transsexuality is a condition in which a person believes that they are trapped in a body of the wrong sex. Many transsexuals undergo surgery and hormone therapy to correct this, but the cause of transsexuality is still unknown. Some scientists believe that it is caused by a birth defect, while others believe that it is the result of a psychological condition. There is no evidence to support either theory.
It is possible that transsexuality is caused by a combination of genetic and environmental factors. For example, a person may be born with a genetic predisposition for transsexuality, but the condition may not be triggered until later in life by a traumatic event. Alternatively, a person may be born with normal sexual anatomy, but experience a hormonal imbalance during puberty that leads to the development of transsexuality.