The reasons that people are the way they are are extremely important to some people. Nobody knows exactly why this is.

The Savvy Psychologist, Ellen Hendrikson, at Scientific American, has been asked to explain why some people are transgender.

Generally the answer for why people are the way they are breaks down to 1) nature, 2)nurture, 3) somewhere in between or 4) sin, depending on the positioning of the observer. 3) often is the safest bet.

Being transgender, however, seems not to be one of these things. While the research is still in its infancy, so far, the answer is overwhelmingly: nature.

One recent finding (2010 is not that recent, and the finding has been expected for a very long time) is that anatomical sex, gender identity, and sexual orientation are all determined in the womb. Everything is set before birth and in sequence. Sexual anatomy happens first, in the first six weeks of development. But once anatomy is settled, there’s a big time lag—until about six months gestation—before the brain masculinizes or feminizes. At that point, if exposed to a testosterone surge, a fetal brain’s nerve cells develop in a male direction—a male gender identity. In the absence of such a surge, the brain develops in a female direction—female gender identity. And last but not least, sometime between six months and delivery, sexual orientation is set in the brain through an as-yet unknown combination of genetics, hormones, and the uterine environment.

So why don’t genitals always match the brain? The definitive answer is still beyond the reach of science, but there are three factors that may determine where one falls on the gender identity spectrum:

#1: Genetics:

In a 2012 review, researchers scoured the world for twins in which one or both twins were transgender. In the identical twin pairs, meaning twins with exactly the same genetic information, 39% were both transgender. Of the fraternal twins, where each sibling is genetically unique, how many were both transgender? Exactly zero. The much higher likelihood of both twins being transgender if they are identical versus fraternal implies that genes play a role in determining transgenderism. What’s more, a study in the journal Biological Psychiatry actually found a gene variant associated with being a transgender woman.

#2: The Uterine Environment

But wait, you say, shouldn’t identical twin pairs be the same? If one identical twin is transgender, shouldn’t the other? How do you account for the 61% of identical twin pairs where only one is trans? Again, the scientific jury is still out, but a probable answer lies in the prenatal environment, aka the womb. Identical twins may share genetic codes, but their epigenomes—which of the genes get expressed or remain unexpressed—diverge. Let’s not forget that identical twins have separate umbilical cords, usually have separate amniotic sacs, and develop in different locations in the womb. All these factors can affect the exact dispersion of nutrients, chemicals, and, most importantly, hormones.

#3: Brain Structures

Brains are shaped by experience, so neuro-imaging of adult trans brains is somewhat problematic.

a 2014 study in the Journal of Neuroscience found that differences in the brain’s white matter tracts fell along a perfect spectrum of gender identity with cisgender men and women at the ends and trans men and women in the middle.

One important note is that a factor not on this list is nurture. So far, the role of the environment seems to be tiny. Back in the day, a transgender identity was thought to be the result of some sort of early trauma. Families, especially mothers, were wrongfully blamed. But as biological evidence mounts, the role of the environment shrinks, which explains why conversion therapies, whether for gender identity or sexual orientation, are increasingly considered ineffective at best, and harmful at worst.

OK, so if gender identity is biological and set before birth, why is there a mental health diagnosis associated with being transgender?

Gender dysphoria is a diagnosis that connects transgender people with the health care system when it is necessary to treat the harm caused by interaction with an often hostile society.

People are people. People vary in their physical and mental characteristics, none of which makes then "not people." "Target for hate" should never be an unquestioned human label.