There is uncertainty regarding the actual cause or causes of HBS. Some might say people with HBS are born with souls of the opposite gender to their bodies, which may be true, but it is not verifiable scientifically.

Others consider it simply a problem concerning upbringing, which seems unlikely, given that it has occurred throughout history in all societies and social classes.

However, the most plausible explanation is that people with HBS have neurological structures that do not match the gender of the rest of their bodies, due to some genetic or hormonal irregularity.

When a human egg is fertilised by a sperm, a new life begins from a single cell containing a mixture of DNA from both parents. This DNA usually contains either the chromosome pair XX or the pair XY.

The cell replicates itself, and after a while the cells separate into three distinct groups. One group shall later form the skin, nervous tissue, and brain. Another group shall form bone, blood, and muscle. The third group shall form most internal organs.

A placenta forms to connect the embryo to its mother. This transfers substances such as nutrients from the mother’s blood stream to the embryo, and produces hormones to regulate the development of the embryo.

There is little understanding of the process that the embryo uses to develop gonads that shall later differentiate into either testes or ovaries, but we know that it involves hormones and the XX or XY chromosomes.

The embryo also develops the beginnings of both male and female internal reproductive structures, one of which is resorbed into the body depending on the presence of certain hormones.

The presence of testosterone causes the male structures to develop further, and the presence of AMH causes the body to resorb the female structures. The testes produce both of these factors. In the absence of both hormones, the body resorbs the male structures, and the female structures will develop.

The external genitalia is initially female, but the presence of testosterone causes further development into a male configuration. Often, there is a seam where the proto-labia fused itself together on the scrotum and the underside of the penis of adult males.

The sexual differentiation of the brain is not as clear cut, but hormones similarly affect it. The brain develops quite independently from the reproductive system, with the cells that will form the two systems differentiating very early in the development of the embryo.

Sexual differentiation occurs at different times, may involve different hormones and different genes, and involves tissues that may respond differently to the same hormones. The brain is also exceptionally complex, and smaller hormonal variations could affect it much more than other parts of the body.

The DNA of the embryo is essentially the blueprint from which it develops. This outline contains much more information than the embryo shall actually use. Genetic abnormalities can cause errors in the parts of the chart that the embryo is using, or tell it to use the wrong parts of the pattern.

Therefore, some parts of the body might not make required changes when sexual hormones interact with them. In addition, the presence of hormones at different developmental stages of the embryo helps regulate the following of the DNA blueprint.

The embryo shall not develop as expected if we introduce incorrect hormones at critical times, such as when the mother takes certain forms of medication. On the other hand, natural factors may prevent the correct hormones from being present.

The designation for abnormalities in sexual differentiation as a group is Intersexuality. Androgen Insensitivity Syndrome (AIS) is a good example. Embryos with Total AIS do not recognise testosterone, so their external genitalia are female. However, AMH affects them normally, so if they have XY chromosomes they will not develop female internal organs such as the uterus.

HBS is a form of intersexuality in which the brain of a person with XY chromosomes fails to masculinise for some reason. Conversely, the brain of a person with XX chromosomes does masculinise. This can happen in many ways.

Other signs of mild atypical sexual differentiation often, but by no means always, accompany it. That is, there may be a particularly large clitoris or small penis, unusually pronounced proto-labial seam, late or minimal puberty, etc.

It can also coexist with other types of intersexuality, although if another variety of intersexuality were present, most would think an additional diagnosis of HBS superfluous.

Technically speaking, this makes the neurological gender identity of a person with HBS the thing that is anomalous, unless their brain matches their chromosomes, and everything else is wrong, but that is not common. However, the brain is by far the most important part of the body; the rest is merely a shell to keep the brain alive.

While the gender identity of a person with HBS may not be what their DNA intended, their body is in a perfectly normal and healthy state. For all practical purposes, their brain development is normal, and their bodily evolution is in error.

The XX/XY chromosomes do affect the sexual differentiation of the embryo, but are by no means the only factor, and are not a useful means of determining a person’s actual neurological gender.

In some species, chromosomes are completely irrelevant, and the incubation temperature of the eggs determines sexual differentiation. Members of other species naturally change their sex during their lifetimes.

Women with HBS seems to be more common than men with the condition, although no consensus exists as to the exact ratio. This is a natural consequence of human development being female by default, for it is generally easier for something to fail to happen when it should than for something to happen when it should not.

One situation in which the cause of Harry Benjamin Syndrome is quite clear is the sexual mutilation of children or infants. This most often occurs with physically intersexed infants, where the individual is operated on to make them conform more closely to a sex chosen by a doctor with no possibility of consent or regard for their neurological gender identity.

It can also occur if there is accidental damage or removal of a male infant’s penis, and it is easier to surgically transform him into a female, and raise him as such, than it is to reconstruct the penis. It is common for people in these situations to be very unhappy with this situation, and often they revert to living according to their actual neurological gender later in life.

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