- next gonadal differentiation (ovaries or testes),
- next differentiation of the internal and external genitalia (physical genital
formation) and - finally the differentiation of the brain into male or female (brain-sex).
In an XY foetus ( usually male ) - an XY chromosomal pattern (chromosomal
configuration), testis (gonadal development), male internal and external genitalia and
finally a male brain differentiation being the substrate of male type behavior. In an
XX foetus ( usually female ) - an XX chromosomal pattern (chromosomal
configuration), ovary (gonadal development), female internal and external genitalia
and lastly a female brain differentiation being the substrate of female-type behavior.
Most of this physical development takes place in the developing foetus stage before
birth. The last stages of this process of brain sexual differentiation takes place after
birth.
These are in brain structures that only become sex-dimorphic (differentiated)
between the ages of two and four years, well after birth and long after legal
assignment to the male or female sex has taken place. Transsexualism is a disorder
of sexual differentiation: the process of becoming male or female as we
conventionally understand it. It is a condition where the sexual form and structure
(phenotype) of the appearance of a person's body and the genetic construction
(genotype) of a person's body are opposite that of their brain.^1
There are many people for whom not all traditional criteria of physical sex
development are in harmony. For a variety of reasons, one in 80 or so babies is born
with some kind of sex or gender identity anomaly. These are many intersex
conditions which result in a birth with some biological characteristics of one sex and
some of the others. Most intersex conditions are observable at birth, others are not
observable at birth and still others are only discovered much later at puberty.
The predicament of transsexualism means the sexual differentiation of the
brain has not followed the pattern predicted by their earlier steps in the sexual
differentiation process (such as chromosomes, gonad, genitalia) but has
followed a pattern typical of the opposite sex in the final stage of brain
differentiation process.
Like other people born with disorders in this process of sex differentiation, men and
women with transsexualism seek medical rehabilitation for increased harmony with
that of their brain. This decision is similar to the one made in cases of intersexed
children where legal assignment takes place to the sex in which they in all likelihood
will function best.^3 The decision to recommend hormonal and surgical treatment for