A biological basis of transsexualism

What are the assumptions that lead us to conclude that a biological basis for transsexualism exists?

As detailed throughout this website, and especially on the summary page, transsexualism is likely to be caused, influenced and triggered by a multitude of factors, both biological (e.g. genes, epigenetics, gene expression, hormone exposure before and around birth) and social (e.g. cultural issues, gender roles, upbringing). Our psychology, our mentality, our character, our identity are also influenced by both biological and social factors. It’s not either nature or nurture, as the old question goes – it’s both to different degrees.

Many medical conditions, such as allergies, diabetes, autism, disorders of sex development (DSD), Alzheimer’s, neuron diseases, etc. seem to be caused by a multitude of factors, making it impossible to find one single origin. Fortunately, medical science is getting better and better at understanding what predisposes us to certain conditions, and what trigger factors come into play. However, to fully understand all factors and their interdependencies is a long, long way ahead.

We have reason to believe that a biological basis for transsexualism exists. Whether biological processes, for example before and around birth, can be the singular cause of transsexualism, or whether and what other factors can come into play, is being discussed and researched.

To conclude that a biological basis exists, the following seven assumptions need to be true:

  1. Humans come in different genders, including male and female

  2. On average, the two genders have some differences in behaviour and mentality, such as gender behaviour/expression and gender identity

  3. On average, the two genders have some physiological differences, including differences in areas of the brain

  4. Some of those behavioural and psychological differences have their roots in physiology, including areas of the brain that show differences between the genders

  5. The formation of the brain and the body, including areas that show differences between the genders, is partly or fully controlled by biological processes

  6. Biological processes act in different ways and at different times when developing gender differences

  7. These biological processes can masculinise or feminise parts of the body and the brain to different degrees and even in opposing directions

I believe the assumptions are factual. Our current body of knowledge supports each of these assumptions strongly. It is very unlikely that the above processes do not contribute at least partly to the phenomenon of transsexualism.

Please have a look at the reference pages of this webpage, where many studies are listed.

I don’t give evidence for some of the assumptions above (e.g. number 2 – there are some behavioural and psychological differences between male and female) as there is simply so much material around, and they are not disputed anyway. Assumptions 1, 4 and 5 are obviously true, and there is a lot of evidence supporting them.

Assumptions 3, 6 and 7 are the ones I focus on. As you can see on this website, there is a lot of research in many areas including neuroscience, neurology, genetics, endocrinology, psychology and also especially disorders of sex development (DSD) that supports the assumption.

Anyway, like I say on the summary page, the most important question for an individual affected by gender dysphoria is how quality of life can be improved, and not what the root cause might be.

However, I believe that research and knowledge will help us in finding remedies, better treatment and also in increasing social acceptance and discrimination.

No matter what the cause, transsexualism is part of the identity of some people. That identity cannot be changed – and even if it was possible to change, it would raise grave moral questions. All humans are equal and all human experience has the same worth.


The main body of evidence is listed on the four main reference pages:

What is transsexualism? | What causes transsexualism? | What helps?

More evidence: Disorders of sex development (DSD)

A summary of the findings of the reference pages is given here: Summary

More references can be found here (articles not directly relevant to the observations discussed on the main reference pages): Other references

A short discussion regarding possible contradicting evidence is here: Evidence against?

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