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Biology 202, Spring 2005 Third Web Papers On Serendip

The Neurobiology of Gender Bending

Leslie Bentz

In the scientific community as well as the world at large, the concept that there exists physical differences between biological male and female brains is not revolutionary. Extensive research has been done in this field and books such as Men are from Mars, Women are from Venus are evidence of this research boom. Yet surprisingly, still not a lot is known about neurobiological differences between genders. While sex and gender seem to be constantly intertwined and occasionally used interchangeably, the two concepts are not synonymous. Whereas sex is concerned with physical anatomy, gender is concerned with "the behavioral, cultural, or psychological traits typically associated with one sex" ((1)). Gender differentiations are commonly rooted in social constructs, but now it is possible to argue that some gender roles and identities are not purely the result of the environment and society but rather neurobiologically constructed, such as transsexual identities.

Social Constructs of Gender

Traditionally, a rigid dichotomy has been recognized that differentiates between socially acceptable gender identities and perverse identities in Western mainstream society. The stereotypes that plague notions of "women's work" and "men's jobs" have been perpetuated for centuries; leaving women excluded from the most prestigious jobs, and men not seen as adequate caregivers to children. Historian Sherry Ortner summarizes this distinction between socially acceptable gender roles when she argues that men have been equated with culture and the workforce and women to nature and childrearing ((2)). According to Ortner's linear continuum from nature to culture, it is virtually impossible to transcend the borders of each category. Yet for the individuals who do, they find it increasingly difficult to find a nonjudgmental space in which to identify themselves outside of these dominant realms.

In some instances cultures have recognized the presence of a third gender category, which specifically allows these individuals to define their own sense of self. North American Indians are one of several groups to recognize a tri-gender system where the term "berdache" was used to differentiate the intermediate gender role ((3)). Traditionally, berdaches were known to exhibit characteristic behaviors of both genders but predominantly assumed aspects of the opposite sex's chores and lifestyle from childhood. Male berdaches, meaning biological males but gendered females, were most prevalent in these societies and were recognized as sacred and honorable members of their respective groups. Although in the case of berdaches, no biological basis was used in assessing who could rightfully be considered a berdache.

Typically, the berdache status was assumed by individuals who from childhood on through adulthood exhibited behaviors of the opposite sex or who had undergone "supernatural validation, usually in the form of a vision" ((3)). In either case, the identification of berdache was granted based on the feelings of the individual and his/her outward behaviors. No justification beyond these specifications was necessary in recognizing the uniqueness berdaches had to offer their communities.

In most Western or European societies this third sex differentiation is not so easily bestowed upon a person and in many instances straying outside of the gender dichotomy becomes socially unacceptable. Ironically, it was western influence and Carolus Linnaeus' work that encouraged a categorization of life; yet classification has only lead to marginalization for those outside of the heteronormative realm ((4)). Nowadays, individuals who do not feel at ease in their given bodies and who believe their true beings to be of the opposite sex are categorized as transsexuals.

Transsexuality as a distinct category first appeared in Germany in 1923 when Magnus Hirschfeld created the term "transsexualism" ((5)). At this point Hirschfeld "considered TS/TG (transsexual/transgender) persons to be a form of intersex" ((5)). According to Hirschfeld, transsexuality was equivalent or relatable to individuals who were "born with genitalia and/or secondary sexual characteristics of indeterminate sex, or which combine features of both sexes" ((6)). Thus, transsexuality was viewed as having a biological component but was wrongly coupled with hermaphrodites, whereas transsexuality is now viewed as a condition only afflicting anatomically correct individuals.

During this period of scientific exploration, transsexuals were ostracized as a group for not molding into the dominant gender binary of the era. As recently as the 1960s transsexuals were subjected to electro-shock therapies in order to try and "cure" them ((7)). This prejudice against transsexual identities originates from decades old misunderstandings and confusion surrounding non mainstream perverse gender identities. These misconceptions are probably based on stereotypes in which individuals believe transsexuals are merely performing a skewed gender identity and not acting upon an innate identity.

Today, transsexuals are commonly assessed by mental health specialists as experiencing gender identity disorders (GID). Classified as a psychological ailment, manifestations in childhood include a "desire to be the opposite sex, persistent fantasies of being the other sex, a preference for cross sex roles, and/or an intense desire to participate in stereotypical games and pastimes of the other sex" ((8)). Feelings must be intense and must hinder everyday life. The criteria for GID are primarily based on social behaviors and interactions rather than genes or neurobiological components which lead to many questions involving the origin or cause of GID.

The Research that Links Neurobiology and Transsexuality

Although not researched extensively, a small project was undertaken by scientists from the Netherlands that could place a neurobiological explanation behind the feelings of disorientation that transsexuals have about their bodies. The group of scientists published their work nearly 10 years ago but since then similar research has not continued and the investigation into the links between neurobiology and transsexuality have been ignored ((9)). Thus, the ideas which the scientists have explored remain controversial within the scientific community.

This particular study examined the bed nucleus of the stria terminalis (BSTc) in the brain. A part of the amygdala; the BSTc is a component of the Stria Terminalis' "extrinsic subcortical fiber system" ((10)). The test group studied consisted of six male to female transsexuals, homosexual men, as well as heterosexual males and females. The main goal of the research was to weigh and compare the volume of the BSTc in the transsexuals to the control group who exhibited dominant gender role behaviors. Within the control group it was determined that biological males possessed a BSTc 44% larger than their female counterparts: a significant value for such a miniscule portion of the brain ((9)). Next, the size of the bed nucleus of the six female transsexuals was compared to the other male and female participants. Interestingly, "A female-sized BSTc was found in the male-to-female transsexuals" establishing a link between gender identities and biological sex that goes beyond social constructions ((9)).

The group's findings further give validation to the notion that transsexuals are aware from early childhood that their internal thoughts do not coincide with their external appearance. The research is also careful to dispel myths concerned with challengers who may challenge the idea that BSTc volumes are unalterable. Some contenders proposed that the size of the BSTc could be influenced based on elevated testosterone levels and sexual orientation. The research discredited this notion by asserting that the volume of the BSTc was not altered in the males who had been given testosterone supplements ((9)). Sexual orientation was not a contributing factor to BSTc size either since heterosexual and homosexual men had statistically similar BSTc volumes ((9)). Since transsexuality is commonly associated with homosexuality, it is significant that the findings show that regardless of sexual orientation the BSTc of the transsexuals was within the range of their opposite sex group. Thus, BSTc does not appear alterable amongst the transsexuals or control group, thus establishing the possibility of a neurobiological innateness to transsexuality.

Although the research has encouraged a new understanding of gender identities, the experimentation process is inaccessible for everyday application. The only way in which the volume of the BSTc can be measured is postmortem, which is the primary reason why the group's research took 11 years to ascertain ((9)). So currently, the methods used by the Netherlands team will not become mainstream in assessing transsexuality in living patients.

Although a rather obscure study, the data collected by the team was significant in further advancing GID research. With more exposure it may help to dispel myths surrounding the origins of transsexual feelings of otherness. Since the term "transsexuality" was established, the scientific community appeared relatively comfortable with its assessment of transsexuality as a psychological disorder. This study, although not extensive, has rattled the foundations on which transsexuality has traditionally been defined.

The connection between BSTc volume and transsexuality could refute our in-class hypothesis that transsexuality is due to discrepancies between the I-function, or decision maker part of the brain, and the inputs arriving in the central nervous system. Thus, according to the Netherlands team's findings, the hypothesis may have to be reworked to articulate a discrepancy between the inputs into the nervous system and the outputs being generated by the brain and more specifically the bed nucleus of the stria terminalis. Or instead, more probably, transsexuality may be the result of a combination reaction between the I-function and the bed nucleus. At this point in the research, it is too early to conclude that the BSTc is the sole contributing factor in the discombobulating feelings transsexuals experience when trying to make sense of their minds and bodies.

Ultimately, the I-function gives humans the ability to doubt reality and to conceive of the world differently than others do. Essentially, the I-function allows for an immense realm of variation in perceptions, which is essential in conceptualizing gender identities. For transsexuals, their perception of reality forces them to believe that their bodies are not in line with their brains. It is the mixed signals between the physical body and the brain that lead to such confusion. So being able to identify a link between the brain and gender identities would give transsexuals validation for their very existence. For decades these individuals have been living with the reality that their confusion was psychological. Primarily, it has been psychiatrists who have worked with this group. An enormous burden needs to be lifted from these people's souls and minds so that they will not continue to believe they did something to prompt their GID. BSTc size is unchangeable. Transsexual gender identities are fixed within the brain and cannot be altered. Regardless of their efforts to normalize within the dominant heteronormative discourse, the fact remains that their feelings are normal for how their particular brain is composed.

In this instance it appears as though the old truism "mind over matter" must be reversed. Transsexuals are not merely performing a perverse gender identity. These feelings are not a choice and should not be conceived of as perverse or abnormal. It is only with such rigid categorization that transsexuality has come to fall outside of the dominant discourse on socially acceptable gender identities.

Personal Effects

The possibility of innate gender, not primarily learned from experience and social constructs has prompted me to reevaluate how I perceive people and the world at large. After taking several classes centered on gender identities and social norms I came to realize that in all of these classes gender was defined as socially constructed; devoid of biological ramifications. I never questioned the distinction between biology and culture since a biological basis for understanding these differences was never explored. We wrestled with Judith Butler's notions of gender as a performance of self and also how gender becomes a characteristic influenced primarily by nurture instead of nature and dominant social institutions. The work that has been done towards proving the innateness of perverse gender identities forces me to rethink my assumptions. Primarily, I must reconsider the generalizations that were made concerning the astuteness of the gender binary prevalent throughout most of the western world. When we examined instances of difference we saw them as anomalies to the normative homogenous social structure; never being given the idea that a biological third sex/gender grouping could exist. It distresses me that this possibility was never raised and that I was left to assume the universal distinctions to be unquestioningly true.

Granted the study I examined is still the only one of its kind and could be considered controversial, the possibility still exists that their findings will someday be considered universal for all transsexual experiences. From the research that has been published on the links between transsexuality and neurobiology I have been forced to reevaluate many of my most engrained assumptions about gender roles and identity disorders and what causes them to be so prevalent in some individuals and nonexistent in others. Even though I may not completely understand the neurobiology behind the research that has been done to date, it has been invaluable in forcing me to realize what may in fact be the dominant discourse may not always be the true reality of the situation.


1) Dictionary reference site

2) Ortner, Sherry B. "Is Female to Male as Nature is to Culture?" Women, Society and Culture. Stanford, CA: Stanford University Press, 1974.

3) Callendar, C. and L. Kochems. "The North American Berdache." Culture and Human Sexuality. Pacific Grove, CA: Brooks/Cole Publishing, 1993.

4) History of Classification

5) Magnus Hirschfeld

6) Intersex article on Wikipedia

7) Transsexuality article on Warwick Pride website

8) and Gender Identity Disorders, Emedicine

9) A Sex Difference in the Human Brain and its Relation to Transsexuality , J.-N. Zhou, M.A. Hofman, L.J. Gooren and D.F. Swaab

10) Stria Terminalis

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