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The simple version: XX=girl and XY=boy. The presence or absence of testosterone makes the child develop into a boy or a girl. In the second half of the pregnancy a testosterone peak will differentiate a boy, fixing our brains and gender identity for life.


John lost his penis from a botched circumcision at 8 months of age, his testicles were removed and they decided to turn him into a girl. He had girls clothes, psychological counselling, was given oestrogen in puberty. The child developed normally as a female. As an adult, Joan had the sex change reversed, married, adopted children, got separated and committed suicide. - his gender identity hadn't changed.

AIS: androgen insensitivity syndrome. The person produces testosterone but their bodies are insensitive to it. Both the external organs and brain are feminized. They become heterosexual women, even though they are XY.

CAH: congenital adrenal hyperplasia. Girls who have been exposed to a high dose of testosterone in the womb and have such a large clitoris they sometimes are registered as boys. They almost always are assigned a female gender, but 2% acquire male gender identity in the womb.

The preference of dolls or cars isn't forced by society, it's programmed in our brains to prepare us for our roles in life, even in monkeys the same choices are made. Girls are prepared for motherhood and boys for fighting and technical tasks.

The peak in testosterone is responsible for this. Girls with CAH are more boisterous and may be called tomboys.

Eye contact between women during negotiations leads to a better outcome, between men it prevents coming to terms. Men also prefer to sit side by side rather than face to face. Side by side is more friendly, as though they are on watch together.

How can homosexuality still be in genes? Heterosexual individuals with the same genes produce a larger-than-average number of offspring, keeping the genes in circulation and this may be a reason.

Girls with CAH are more likely to be bi or homosexual.

The more older brothers a boy has, the greater the chance for him to be homosexual. The mother's immune response to male substances produced becomes stronger with each pregnancy.

Pregnant women suffering from stress release cortisol with affects foetal sex hormone production.

The biological clock is twice as large in homosexual men.

Sexual orientation is determined by many structural and functional brain differences, all of which develop in the womb the second half of pregnancy, and which cannot be changed by the post-birth environment.

Transsexuality: feeling you have been born in the body of the wrong gender. Sex organ differentiation happens in the first months. Brain sexual differentiation happens in the second half of the pregnancy. Since they are separate events, they can be influenced independently of one-another.

BST- bet nucleus of the stria terminals is an area involved in many aspects of social behaviour. It is twice as large in men as women. In transsexuals, it is the opposite.

Sudden pedophilia may have many causes: a brain tumour in the prefrontal cortex, temporal cortex, hypothalamus, it may be a symptom of dementia, brain infections, Parkinsonism, multiple sclerosis, brain trauma, partial removal of the anterior lobe during operations to cure epilepsy.

Deviant sexual behaviour is displayed in 18% of first degree relatives of pedophile men, suggesting it may also be genetic.

There is less grey matter in the hypothalamus, the bed nucleus of the stria terminals, amygdala of pedophiles.

The smaller the amygdala, the more likely to commit pedophilic crimes.


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