The author wrote "Similarly, although the incidence of transgenderism is much lower than same-sex attraction, twin studies show that the condition is not genetic per se."

Which studies would these be, then? Because the actual, not made up, studies say something quite different.

Transsexuality Among Twins: Identity Concordance, Transition, Rearing, and Orientation, Diamond M, International Journal of Transgenderism, 14:1, May 2013, pp 24-38

-- The relative contributions of genetic and environmental factors to the development of gender identity have been debated. Twins were studied that are concordant or discordant for gender identity status in order to provide clarification of this issue. An extensive library search yielded reports of 27 male and 16 female sets concordant or discordant for transsexuality. An Internet bulletin board search and clinical contact requests for participants in a survey of twins in which one or both transitioned located 69 new twin pairs. In addition to asking about matters associated with gender, these new twins were asked about their transition, rearing, and sexual practices. Combining data from the present survey with those from past-published reports, 20% of all male and female monozygotic twin pairs were found concordant for transsexual identity. This was more frequently the case for males (33%) than for females (23%). The responses of our twins relative to their rearing, along with our findings regarding some of their experiences during childhood and adolescence show their identity was much more influenced by their genetics than their rearing.--

An earlier work reviewed hormonal vs genetic factors.

Gender Identity Concordance Among Monozygotic and Dizygotic Twin Pairs, Diamond M, Abstract for World Professional Association for Transgender Health Symposium, Atlanta, GA. 24-28 Sept. 2011

--

The relative contributions of genetic and other factors to the development of gender identity are still being debated. We studied twins, over the age of 10 who were concordant or discordant for gender identity status in order to provide clarification of this issue. An extensive literature search yielded 24 studies of monozygotic (MZ) twin pairs (14 male, 10 female) who were discordant or concordant for transsexuality. In addition, Internet requests for participants and clinical contacts of the author located 55 new pairs of twins: 18 monozygotic male pairs, 16 monozygotic female pairs, 8 dizygotic (DZ) male pairs and 13 dizygotic female pairs. The dizygotic twins included 2 male/female pairs.

From the literature, 8 of the 14 (57%) monozygotic male pairs were found to be concordant for transsexual gender identity and 4 of the 10 (40 %) female pairs were concordant. From our survey, 5 male monozygotic pairs out of 18 (28%) were identified as concordant for gender identity. Three of 16 sets of female MZ twins (19 %) were identified as concordant. Among 8 male and 13 female dizygotic twin sets, none were found to be concordant for transsexuality.

Combining data from our independent findings with those from past publications, 13 of 32 male monozygotic twin pairs (38%) were found to be concordant for transsexual identity and 7 of 26 (27%) female MZ twins were found concordant. In comparison, concordance among either male or female DZ twins was only found in one of 27 cases (04%).

These findings support the suggestion that there exists a significant genetic contribution to the development of gender identity disorder. --

The author then goes on to say :

"This idea may align with radical feminist theory, but it is not evidence-based...."

Here's what actual radical feminist theory says. I'll quote from Radical Feminist Professor Janice Raymond. I agree it's not evidence based, but supports exactly the author's equally fact-free views.

Paper Prepared for the National Center for Health Care Technology on the Social and Ethical Aspects of Transsexual Surgery
By Janice G. Raymond
Assistant Professor of Medical Ethics and Women's Studies
Hampshire College/University of Massachusetts
Amherst, Massachusetts
June, 1980

"For this small number of individuals, transsexual surgery is not only a therapeutic necessity but a reasonable and humane treatment. Furthermore, the majority of postoperative reports of transsexuals testify that the surgery has been proven effective and efficacious and is therefore no longer experimental. They cite the fact that 90% of those persons who have undergone surgery report that their lives are happier and healthier.
These reports, however, do not explore the deeper social issues, nor do they question a satisfaction that is achieved at the expense of never investigating the underlying social and ethical issues. They do not state that after surgery the transsexual fits into a role-defined world better than most native-born women who live out their feminine roles....
While there are many who feel that morality must be built into law, I believe that the elimination of transsexualism is not best achieved by legislation prohibiting transsexual treatment and surgery but rather by legislation that limits it and by other legislation that lessens the support given to sex-role stereotyping, which generated the problem to begin with."

They want transsexuals eliminated. It's an article of faith to them too that there can be no biological basis, regardless of the evidence. To continue:

"The issues that this paper has highlighted should by no means be confined to the transsexual context. Rather they should be confronted in the "normal" society that spawned the problem of transsexualism to begin with."

Rather than being on opposing sides, both the Radical Lesbian Feminists and Family Voice Australia are of like mind here.

In addition to genetics, hormonal environment in the womb plays a role.

-> Prenatal exposure to diethylstilbestrol(DES) in males and gender-related disorders:results from a 5-year study Scott Kerlin. Proc. International Behavioral Development Symposium July 2005

46,XY foetuses exposed to DES in the womb have a 500 times greater rate of transsexuality.

This is a congenital anatomical issue.

-> A sex difference in the human brain and its relation to transsexuality. by Zhou et al Nature (1995) 378:68–70.
-- Our study is the first to show a female brain structure in genetically male transsexuals... --

--> Male–to–female transsexuals have female neuron numbers in a limbic nucleus. Kruiver et al J Clin Endocrinol Metab (2000) 85:2034–2041
"The present findings of somatostatin neuronal sex differences in the BSTc and its sex reversal in the transsexual brain clearly support the paradigm that in transsexuals sexual differentiation of the brain and genitals may go into opposite directions and point to a neurobiological basis of gender identity disorder."

Paul McHugh (who the author quotes) wrote in "Psychiatric Misadventures," The American Scholar, (Autumn, 1992), pp.
497-510.
"We have to learn how to manage this condition as a mental disorder when we fail to prevent it. If it depends on child rearing, then let's learn about its inner dynamics so that parents can be taught to guide their children properly. If it is an aspect of confusion tied to homosexuality, we need to understand its nature and exactly how to manage it as a manifestation of serious mental disorder among homosexual individuals."

Both Gay and Straight Transpeople exist. So much for the "form of homosexuality". The whole idea of a "psychiatric" cause has been repeatedly debunked in numerous experiments over 60 years.

From the Medical Standards of Care v7 2011:
"Treatment aimed at trying to change a person’s gender identity and expression to become more congruent with sex assigned at birth has been attempted in the past without success (Gelder & Marks, 1969; Greenson, 1964), particularly in the long term (Cohen-Kettenis & Kuiper, 1984; Pauly, 1965). Such treatment is no longer considered ethical.

Candide - There is no real social "issue" because the condition is rare. There is a real (but rare) condition. The issue is invented because it fits neatly into the Left's belief in gender warfare and wedge issues. There are thousands of more common conditions which are ignored because they have no political "wedge" value and therefore warrant no airtime.

No doubt it will become more popular over time

>>Transgender treatment, like anorexia treatment, may take many years. It is best begun early. Schools should not, by policies which reinforce body misperceptions, delay the process.<<

Now there I agree with the author. However, what she proposes as "treatment" she doesn't say. The kind of treatment she apparently has in mind results in children dying. It is unethical. It has been shown repeatedly not to work - though there's a plethora of religious propaganda pieces baldly asserting that it does. They just haven't bothered testing this assertion, not once in the last 40 years. It's an article of faith in the most literal sense.

In contrast, there are multiple studies - actual measurements of large numbers of cases - showing that the treatment she espouses is harmful, and that that she wishes to be discontinued on religious grounds *does* work. Moreover, the earlier this treatment commences, the better the outcome. Better late than never, but better early than late.

See
The treatment of adolescent transsexuals: changing insights. Cohen-Ketternis et al, J Sex Med. 2008 Aug;5(8):1892-7.

"From these studies it appeared that the youth who were selected for early hormone treatment (starting between 16 and 18 years) no longer suffered from gender dysphoria, and that 1–5 years after surgery, they were socially and psychologically functioning not very different from their peers. Their scores on various psychological instruments, such as a shortened Dutch form of the Minnesota Multiphasic Personality Inventory and the Symptom Check List-90, were considerably more favorable than scores of a group of subjects who had been treated in adulthood in the Amsterdam clinic, and scores were in the normal range as compared to normative samples."