Transgender, or transsexualism, a condition in which the individual defines him or herself as male or female in opposition to their physical gender, or feels strongly that he or she wants to live as a member of the other gender, is rare. By some estimates, no more than 1 person in 350,000 believes he or she was born the wrong gender.
As they progress through childhood, their inability to relate to their own gender identity increases. Some seek the advice of a physician, and by the time they reach early adulthood, begin to take medical action to alter their gender.
Since more males than females are diagnosed as transsexuals, it is more common for males to receive hormone treatment to develop secondary sex characteristics, such as breasts.
In some cases, a surgical procedure is performed to alter the male sex organs to physically complete the transformation from one gender to the other.
At the Netherlands Institute for Brain Research in Amsterdam, scientists studied six male-to-female transsexuals and found evidence that a section of the hypothalamus that controls sexual function appeared to be more like the type found in women than that found in men.
Because human embryos destined to become males differentiate early in the development process, the Netherlands study raises the question of whether the developing embryo could receive mixed hormonal signals to portions of the brain and the developing genitalia. Thus, as of the late 1990s, research seems to indicate that there may be physical reasons for transsexualism.