That's a question I have been asked dozens of times.
And other questions pop into my head. Why is water wet? Why are blueberries purple? I spend about as much time considering each of those queries.
I've written about this in the past: Layers of Why.
After extensive introspection I basically came up with this:
If I had to pick a single step in my growth process as a human being, it would be the moment when it occurred to me that it didn’t matter why I was the way I was. What mattered was that I existed, that I was a human being and I was living my life the best way I knew how.
But that is not good enough for some people. That set would especially contain those who exhibit little respect for science, but still demand a scientific explanation for the existence of transpeople...which still probably wouldn't be good enough, because, you know, God.
Recently Sabrina Rubin Erdely of Rolling Stone took a stab at the science.
Once upon a time, the thought was that transgender was caused by childhood trauma of some sort. Our families were dysfunctional or we were sexually abused as children. But while our families may or may not have been dysfunctional, that is not how we came to be who we are.
That is absolutely not true at all. But I still get people in my clinic who are trying to unravel what the traumatic incident was, that caused their kid to be trans.
--Dr. Johanna Olson, medical director of the Transgender Clinic at Children's Hospital Los Angeles
The "childhood trauma" that most transfolk suffered, in my not inconsequential experience, was having nobody around who understood how we felt.
More recent research is pointing the finger at biology, rather than childhood trauma.
In 2008 researchers at Australia's Prince Henry's Institute released the results of a study of the genetics of transsexual people. The scientists compared the length of the androgen receptor gene in 112 male-to-female transsexual people with the AR gene in a control group of 250 cisgender men.
A lengthy AR gene is known to make testosterone less effective at signaling and circulating...and just plain functioning. Less potent testosterone could, it was thought, affect the development of the brain in the womb...creating a brain that was "under-masculinized" and more structurally similar to a female brain.
What they found was that that the AR gene tended to be longer in transsexual women than it was in cisgender men.
This new evidence is supported by a few previous studies that have found that male-to-female transsexuals have other biological similarities to women; they tended to have fewer somatostatin (growth regulating) neurons than the average man, for example, and the ratio of their index and ring fingers (also known as 2D:4D, a common proxy for androgen exposure in utero) was higher than it usually is in men, closer to the average female ratio.
Studies in cells show the longer version of the androgen receptor gene works less efficiently at communicating the testosterone message to cells. Based on these studies, we speculate the longer version may also work less efficiently in the brain.
--Professor Vincent Harley, lead researcher
The results were not conclusive: not all transsexual women had the longer AR gene and some men with a longer AR gene did not have known gender identity issues. That suggests that perhaps another gene is also involved...or that there is a combination of genetic and psycho-social factors.
It's a very tough condition. These people are often on the margins of society, are ostracised, poor, unemployed. It's not something you would want to choose yet still some people think it's a choice when it's more likely transsexuals are born like that.
--Harley
This study appears to reinforce earlier studies which have indicated that, in some trans people, there may be a genetic trigger to the development of an atypical gender identity.
However, it may be just one of several routes and, although it seems extremely likely that a biological element will always be present in the aetiology of transsexualism, it's unlikely that developmental pathways will be the same in all individuals.
--Terry Reed, Gender Identity Research and Education Society
People develop an inner sense of being male or female from an early age but transsexuals identify with a physical sex opposite to their biological sex. Some theories suggest some causes that include psychosocial factors including dysfunctional family dynamics and traumatic childhood experiences. But research is increasingly implicating biological factors including family history and genetics.
The present study would disapprove the social stigma that trans-sexualism is simply a lifestyle choice; the findings support a biological basis of how gender identity develops.
--Ground Report
Erdely also notes that recent Spanish brain scan studies have shown that the white matter in non-treated transmen looks much like that of birth-assigned males. They also found that the amount of white matter of transgender women fell about halfway between that of birth-assigned male and birth-assigned female control groups.
Olson warns that since "those parts of the brain are shaped by performance and experience" the results may be a result of nurture rather than nature. Since a recent survey of identical twins found that only 20% of cases resulted in both twins turn out transgender. so it is unclear what the precise role of genetics is.
Trying to identify causes, whether they be genetic, hormonal, or something else entirely, those studies are underway. The question is, what contributes to the formation of gender identity? It's really complex.
--Olson
But no matter what, we are still valid human beings...no less deserving of equal treatment than other humans.
But this is not a valid assessment for some people. It's time to quote myself again. From an old column I wrote in the mid-90s for Triangle Rising newsmagazine:
Western society, particularly the North American brand, has come up with the idea that life is some sort of contest in which there are winners and losers. At the same time, we are inculcated with the belief that is important to always strive to win in any contest. So people feel they need to prove that their way of living is a winning strategy.
Too many people believe that the only way to do that is to claim that any life that is not lived in accordance with their strategy is the life of a loser. Then they set out to make their belief a reality by making the lives of those they have labeled as losers more difficult.
There is a large group of people who believe that other people should be forced to adopt their life strategy (what they would call "be normal"). Any deviance from their "normality" is viewed with anything from disdain to hatred and may cause them to react with rumor, innuendo, discrimination, verbal, sexual, physical and/or emotional harassment or abuse and, in some cases, even violence.
All this is because it somehow is supposed to make them feel better about themselves and their lot in life.