Sex & Gender Flashcards
Transgender Brain Science - Various
Intersex Is Not As Common As Red Hair - Colin Wright; Reality’s Last Stand; 2020
- Claim of 1.7% Prevalence of Intersex People
• Commonly cited by human rights organizations and LGBTQ+ advocates.
• Compared to the prevalence of red hair.
• Originates from Anne Fausto-Sterling’s 2000 book Sexing the Body and her subsequent paper.- Fausto-Sterling’s Definition of Intersex
• Broadly includes any deviation from a strict “Platonic ideal” of male and female.
• Based on chromosomal, genital, gonadal, or hormonal variations.
• Estimated 1.7% prevalence, potentially as high as 2.27% with more inclusive criteria. - Criticism of the 1.7% Figure
• Leonard Sax (2002) argues the statistic is flawed and overly broad.
• Includes conditions not clinically recognized as intersex, such as:
• Late-onset adrenal hyperplasia (LOCAH) – 88% of Fausto-Sterling’s total.
• Klinefelter syndrome, Turner syndrome (sex chromosome variants without ambiguous genitalia).
• Vaginal agenesis (XX females with normal ovaries, capable of childbirth). - Revised Intersex Prevalence
• When intersex is strictly defined as “chromosomal sex inconsistent with phenotypic sex” or “phenotypically unclassifiable as male or female,” the prevalence drops to 0.018%—almost 100 times lower than Fausto-Sterling’s estimate. - Conclusion
• While intersex individuals deserve recognition and fair treatment, inflating statistics to 1.7% misrepresents biological reality.
• Advocating for rights should not rely on misleading data but rather on ethical treatment principles.
- Fausto-Sterling’s Definition of Intersex
(Leonard Sax is an American physician and psychologist known for his work on gender differences in education, child development, and biology. He holds both an M.D. and a Ph.D. in psychology and has written extensively on topics related to sex differences, education, and parenting.
Key Facts About Leonard Sax
• Education: Earned his medical degree and Ph.D. from the University of Pennsylvania.
• Career: Worked as a family physician and later transitioned into research and writing.
• Books:
• Why Gender Matters (2005) – Discusses biological and psychological differences between boys and girls.
• Boys Adrift (2007) – Examines the factors leading to the decline in motivation among boys.
• Girls on the Edge (2010) – Explores challenges faced by modern girls, including mental health and social pressures.
• The Collapse of Parenting (2015) – Argues that modern parenting trends are leading to weaker family structures and less resilient children.
• Criticism of Fausto-Sterling’s Intersex Statistic:
• In 2002, Sax published How Common is Intersex? as a response to Anne Fausto-Sterling’s claim that 1.7% of the population is intersex.
• He argued that her statistic was overly broad and included conditions not clinically classified as intersex.
• Using a stricter definition, he estimated the actual prevalence of intersex to be about 0.018%.
Sax’s work is often cited in debates about gender, sex differences, and education, though his views have sometimes been controversial, particularly among scholars in gender studies).
Transgender Brain Studies are Fatally Flawed - Colin Wright & Others; City Journal; 2025
Key Points and Data from the Article
1. Flawed “Transgender Brain” Hypothesis • The belief that transgender individuals have brains resembling the opposite sex is based on misinterpretations of scientific studies. • This narrative has influenced both personal medical decisions and public policy. • Legal and medical professionals often use this claim to justify “gender-affirming care.” 2. Case Study: Yarden Silveira • Yarden, a detransitioner, believed he had a “female brain” and underwent gender-related surgeries. • He ultimately suffered severe medical complications and died. • His belief in the “female brain” concept was reinforced by scientific literature and popular media. 3. Use of “Brain Sex” in Legal and Medical Fields • Civil rights activists argue that transgender identity is biologically innate, similar to race. • Courts and gender clinicians use brain sex studies to support gender-affirming care. • Example: Daniel Shumer, a pediatric endocrinologist, testified in favor of trans medical interventions, citing brain structure similarities between transgender and non-transgender individuals with the same gender identity. 4. Media and Popular Culture Reinforcement • The idea of a “brain-body mismatch” is widespread in news, TV, and books. • Examples: • Law & Order: SVU (2009) presented the theory as a scientific fact. • I Am Jazz (children’s book) states, “I have a girl brain but a boy body.” • 49.2% of detransitioners in a forthcoming survey recalled doctors using “male brain in a female body” rhetoric. 5. Scientific Flaws in Transgender Brain Studies • Many studies fail to control for sexual orientation, which correlates with brain structural differences. • Studies cited in support of brain sex theory: • Lajos Simon et al. (2013) – Found cross-sex brain shifts but didn’t control for sexual orientation. • Eileen Luders et al. (2009) – Found no overall difference in brain structures between male-to-female transgender individuals and male controls. • Ivanka Savic & Stefan Arver (2011) – Controlled for sexual orientation and found brain differences were not clearly feminized or masculinized. 6. Key Finding: Sexual Orientation Confounds Results • Gay and lesbian individuals also show cross-sex shifts in brain structure. • When properly controlling for this factor, the supposed transgender brain differences diminish or disappear. • The proportion of homosexual participants in a study directly correlates with the size of the reported cross-sex shift. 7. Inconsistency in the “Brain Sex” Argument • The LGBT movement rejects the idea of a “gay brain” requiring medical intervention. • However, they embrace the idea of a “transgender brain,” despite similar research flaws. 8. Policy and Ethical Concerns • The transgender brain hypothesis has led to irreversible medical interventions. • Many transgender-identifying individuals later detransition and regret their treatments. • Policy recommendation: Independent scientific reviews should be mandated before endorsing medical transition as a biological necessity.
Conclusion
• The “brain sex” hypothesis is scientifically weak and fails to hold up when accounting for sexual orientation.
• The narrative has serious medical and ethical consequences, leading young people toward irreversible treatments.
• Public policy should be based on rigorous, unbiased research, not politically or legally motivated claims.
(Colin Wright is an evolutionary biologist, writer, and editor known for his work on sex differences, gender identity debates, and critiques of gender ideology. He has a background in academia and has been active in public discourse on controversial social and scientific topics.
Key Facts About Colin Wright
• Education & Career:
• Holds a Ph.D. in evolutionary biology from the University of California, Santa Barbara.
• Formerly an assistant professor of evolutionary biology at Penn State University.
• Left academia due to concerns about ideological influences in science.
• Writing & Public Advocacy:
• Writes on sex and gender debates, particularly critiquing gender identity ideology from a biological perspective.
• Has contributed to publications such as City Journal, The Wall Street Journal, and Quillette.
• Frequently challenges claims that biological sex is a spectrum or that gender identity has a clear biological basis.
• Current Work:
• Editor at Reality’s Last Stand, a Substack publication focused on sex, gender, and science.
• Advocates for clear definitions of biological sex in science and policy discussions.
• Active on social media, engaging in debates on sex differences, transgender issues, and scientific integrity.
Public Perception & Controversy
• Wright is a polarizing figure in gender discourse.
• Critics accuse him of transphobia or misrepresenting scientific research to push a political agenda.
• Supporters view him as defending scientific accuracy against ideological distortions).
What Science Says About Transgender Identity and the Brain - TransVitae; 2025
Key Points and Scientific Findings from the Article
- Brain Development and Transgender Identity
• Gender identity is biologically rooted, supported by brain studies showing differences between transgender and cisgender individuals.
• Brain structures of transgender individuals often resemble those of the gender they identify with, not the sex assigned at birth. - Studies Supporting the “Transgender Brain” Hypothesis
• 1995 Study on BSTc (Bed Nucleus of the Stria Terminalis, Central Subdivision)
• Found that transgender women’s BSTc size and neuron counts were similar to cisgender women, not cisgender men.
• BSTc is involved in sexual behavior and gender identity.
• These differences were independent of hormone therapy (HRT).
• MRI Studies on White Matter and Brain Connectivity
• Show that transgender women’s brain structures fall between male and female norms, with patterns more similar to cisgender women than cisgender men.
• Cortical thickness, white matter microstructure, and activation patterns support the idea that transgender brains diverge from their birth-assigned sex.
• 2008 Functional Brain Study
• Found that transgender women who had not started HRT exhibited female-typical hypothalamic responses to pheromone-like odors, distinct from cisgender men.
• Similar results were observed in transgender adolescent girls, suggesting these differences emerge early in life. - Transgender Men and Brain Development
• Diffusion Tensor Imaging (DTI) Studies
• Found transgender men’s white matter structure was distinct from cisgender women and more aligned with cisgender men.
• Differences in subcortical brain structures also placed transgender men closer to male norms.
• Suggests gender identity has a biological basis beyond social conditioning. - Non-Binary Identities and Brain Development
• 2020 Study on Gender-Incongruent Individuals
• Found unique brain connectivity patterns distinct from both cisgender men and women.
• Suggests gender identity exists beyond the male-female binary.
• More research is needed to understand the neurobiology of non-binary identities. - The Effect of Hormone Replacement Therapy (HRT) on Sexual Orientation
• HRT can influence sexual attraction, but the extent varies.
• Studies on HRT and Sexual Orientation Changes:
• 2014 Study:
• 32.9% of transgender women and 22.2% of transgender men reported shifts in sexual attraction after transitioning.
• 2013 Study:
• 58.2% of transgender and gender-nonconforming individuals reported changes in attraction over their lifetime.
• Transgender men on testosterone often report increased libido and newfound attraction to men.
• Transgender women on estrogen frequently experience decreased libido and shifts in attraction. - Addressing the “What is a Woman?” Question
• Science shows that gender identity is more than chromosomes or reproductive capacity.
• Transgender women’s brains align more closely with cisgender women than cisgender men.
• Womanhood should not be defined solely by reproductive function, as it is a social and neurological identity shaped by biology, psychology, and lived experience. - Policy and Social Implications
• These findings validate transgender identities, demonstrating that being transgender is not a choice, but biologically ingrained.
• Understanding gender identity through scientific research supports legal protections, medical care, and social acceptance.
• The research underscores the need for dignity, equal rights, and recognition of transgender people.
Conclusion
• Brain studies confirm that transgender individuals are neurologically distinct from cisgender individuals of their assigned sex.
• Gender dysphoria has measurable biological underpinnings.
• HRT helps align an individual’s body with their neurological and hormonal identity, reducing distress.
• Science supports the lived experiences of transgender individuals, and society should follow suit by ensuring respect, rights, and understanding.
Transgender Youth Have Better Emotional Health after Taking Hormones, New Study Finds - Scientific American; 2025
Key Findings and Scientific Data from the Article
- Mental Health Crisis Among Transgender Youth
• Suicide attempts among transgender and nonbinary youth increased by up to 72% (2018–2022) in states that restricted trans rights.
• Transgender youth experience higher rates of depression, anxiety, self-harm, and suicide compared to non-trans peers.
• A 2022 study found that trans youth who received gender-affirming care had:
• 60% lower odds of depression
• 73% lower odds of suicidality over a 12-month period - New Study on Emotional Health and Hormone Therapy (Journal of Adolescent Health, January 2024)
• Study followed 315 trans youth (ages 12–20) over two years after starting hormone therapy (testosterone or estrogen).
• Five areas of emotional health improved significantly:- Psychological well-being (overall happiness and mental health)
- Self-efficacy (belief in one’s ability to achieve goals)
- Social satisfaction (friendship quality, emotional support, loneliness)
- Negative social perception (hostility and rejection)
- Negative affect (anger, sadness, fear)
• Results after 6 months of hormone therapy:
• Participants’ scores in friendship and life satisfaction improved to healthy levels.
• Greater appearance congruence (alignment of physical presentation with gender identity) correlated with improved emotional health.
- The Impact of Puberty Blockers vs. Late Puberty
• Trans youth who accessed puberty blockers or had late-onset puberty had better mental health before hormone therapy than those who had already undergone significant pubertal changes.
• Possible reasons:
• More supportive families (who can afford puberty blockers)
• Avoidance of unwanted secondary sex characteristics like breast growth or facial hair - State and Federal Restrictions on Gender-Affirming Care
• 23 states have banned gender-affirming care, and two additional states have banned surgeries for minors.
• Trump’s executive order (temporarily blocked by federal judges) aims to:
• Cut federal funding for hospitals that provide gender-affirming care.
• Exclude gender-affirming care from Medicaid coverage.
• Label gender-affirming care as “junk science.” - Medical Community’s Support for Gender-Affirming Care
• Major medical organizations support gender-affirming care, including:
• American Academy of Pediatrics
• American Medical Association
• Endocrine Society
• These organizations argue that decades of research confirm gender-affirming care is safe and effective.
• An amicus brief to the Supreme Court stated that medical treatment for gender dysphoria is “safe and effective when provided to appropriately identified individuals.” - Safety and Long-Term Effects of Hormone Therapy
• Gender-affirming hormones have been used for decades to treat other medical conditions (e.g., hypogonadism) without major safety concerns.
• Hormone therapy risks are minimal and comparable to normal biological sex differences:
• Estrogen therapy for transgender women increases blood clot risk to female baseline levels.
• Testosterone therapy for transgender men does not appear to permanently impair fertility, with some being able to conceive after stopping treatment.
• Estrogen’s impact on sperm production is less studied but has some permanent effects. - The Reality of Regret and Detransition Rates
• Gender-affirming hormone use is rare in adolescents and is not prescribed before age 12.
• Regret rates are extremely low:
• A four-year study found that only 0.5% of trans adolescents who started hormones later detransitioned due to re-identifying with their birth-assigned gender.
• Fertility preservation options are available, including:
• Sperm and egg cryopreservation
• Testicular and ovarian tissue cryopreservation - Conclusion: The Medical Necessity of Gender-Affirming Care
• Gender-affirming hormone therapy significantly improves mental and emotional health.
• Bans on gender-affirming care threaten the well-being of transgender youth.
• Major medical organizations advocate for access to this care, citing decades of research.
• There is no widespread overprescription of hormone therapy for young people.
• The evidence strongly supports the safety, effectiveness, and necessity of gender-affirming treatment.
Update on Biological Sex and Gender Diversity-Related EOs - American Psychological Association; March 2025
Key Points and Scientific Data from the APA Report
- Federal Executive Orders Impacting Transgender and Nonbinary Individuals
• Recent executive orders mandate federal agencies to define “sex” strictly as a binary biological classification determined at birth.
• These orders:
• Restrict gender-affirming care for individuals under 19.
• Withdraw federal funding from programs allowing transgender women in women’s sports.
• Rescind prior protections for gender-diverse individuals.
• Federal agencies complying with these orders:
• Office of Personnel Management: Forms must use only binary sex options.
• Equal Employment Opportunity Commission: No longer allows “X” gender markers.
• Department of State: Suspended passport applications for gender-marker changes.
• Department of Defense: Updating policies to align with binary sex classifications.
• National Park Service & other agencies: Revising terminology in official communications.
• Legal challenges have been filed, addressing:
• Restrictions on gender-affirming care
• Transgender athlete policies
• Passport gender-marker bans
• Regulations affecting transgender individuals in federal prisons - APA’s Concerns and Ethical Dilemmas for Psychologists
• Federal policies conflict with professional guidelines for treating transgender individuals.
• Ethical dilemmas for psychologists:
• Psychologists may be forced to choose between following federal regulations and adhering to evidence-based, ethical practices.
• Psychologists in federally funded institutions could face penalties or legal risks when providing or referring transgender patients to care.
• Insurers may deny coverage for gender-affirming care based on new federal definitions of sex.
• Barriers to Psychological Research and Training:
• Reduced federal funding for studies on gender dysphoria and LGBTQ+ mental health.
• Education and training restrictions for psychologists and mental health professionals. - APA’s Position on Gender Identity and Transgender Health
• APA supports psychological and medical interventions for transgender, gender-diverse, and nonbinary individuals.
• Federal policy changes risk harming entire populations and contradict established psychological science. - Scientific Evidence on Gender Identity and Sex
Biological and Neurodevelopmental Research
• Sex is not strictly binary:
• 1.7% of the global population is born with genital variations (Differences in Sex Development, or DSD/VSC) (Esteban et al., 2023).
• Gender identity is an intrinsic human characteristic (Institute of Medicine, 2011).
• Historical and cross-cultural research confirms non-binary gender identities have existed for centuries (Gill-Peterson, 2018).
• Neuroimaging studies:
• Cortical brain volume in transgender individuals aligns more closely with their gender identity rather than their assigned sex at birth.
• Studies supporting this finding:
• Mueller et al. (2021)
• Nguyen et al. (2019)
Mental Health and Social Factors
• Discrimination and stigma are major risk factors for poor mental health in transgender individuals (Bradford et al., 2013).
• Key protective factors that improve mental health and well-being:
• Self-esteem and pride in gender identity (Mezza et al., 2024).
• Social acceptance and respect for gender identity (Witten, 2003).
• Access to gender-affirming care reduces depression and suicidality.
- Conclusion: The Impact of Policy on Transgender Mental Health
• APA strongly opposes federal policies that erase gender identity and restrict gender-affirming care.
• Scientific evidence overwhelmingly supports the existence of gender identity as distinct from biological sex.
• Discrimination increases mental health risks for transgender individuals, while affirmation and gender-affirming care improve well-being.
• APA urges policymakers to follow scientific evidence rather than politically motivated policies.
(Summaries of Studies Mentioned in the APA Report (With Locations)
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- Esteban et al. (2023) – Differences in Sex Development (DSD) Prevalence
• Location: Conducted by researchers from the University of Granada, Spain.
• Objective: Examined the global prevalence of Differences in Sex Development (DSD), also called Variations in Sex Characteristics (VSC).
• Findings:
• 1.7% of the global population is born with genital variations that do not fit standard male or female classifications.
• Demonstrates that biological sex is not strictly binary.
• Significance: Supports the argument that sex exists on a spectrum, challenging policies that define sex as strictly male or female.
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- Institute of Medicine (2011) – Gender Identity as an Intrinsic Human Trait
• Location: Conducted by the Institute of Medicine, National Academies of Sciences, USA.
• Objective: Investigated gender identity development and its biological, psychological, and cultural influences.
• Findings:
• Gender identity is deeply ingrained and not merely a social construct.
• People can have a gender identity different from their sex assigned at birth.
• Non-binary and transgender identities have existed across various cultures and historical periods.
• Significance: Establishes gender identity as a fundamental human characteristic, reinforcing the legitimacy of transgender and non-binary identities.
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- Gill-Peterson (2018) – Historical & Cross-Cultural Evidence of Non-Binary Identities
• Location: Research conducted at the University of Pittsburgh, USA.
• Objective: Analyzed historical and anthropological records of gender diversity across cultures.
• Findings:
• Many societies historically recognized non-binary and gender-diverse identities.
• Third-gender categories have been recorded in Indigenous cultures, South Asian hijras, and Two-Spirit traditions.
• Significance: Challenges the claim that non-binary and transgender identities are modern social constructs, reinforcing that gender diversity has a historical precedent.
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- Mueller et al. (2021) – Cortical Brain Volume in Transgender Individuals
• Location: Conducted at University of Vienna, Austria.
• Objective: Used neuroimaging (MRI scans) to examine cortical brain volume in transgender individuals.
• Findings:
• Transgender individuals’ brain structures more closely resemble their gender identity rather than their assigned sex at birth.
• These differences exist even before hormone therapy.
• Significance: Provides biological evidence that gender identity has a neurodevelopmental basis, countering arguments that it is purely psychological or social.
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- Nguyen et al. (2019) – Brain Differences in Transgender Individuals
• Location: Conducted at University of São Paulo, Brazil.
• Objective: Used MRI scans to analyze neural connectivity and brain structure in transgender individuals.
• Findings:
• Transgender individuals exhibit neuroanatomical features aligned with their gender identity.
• Brain connectivity patterns differ from both cisgender men and women, indicating a unique neurodevelopmental trajectory.
• Significance: Strengthens the argument that gender identity is neurologically rooted and not merely a choice or psychological condition.
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- Bradford et al. (2013) – Discrimination and Transgender Mental Health
• Location: Conducted at Virginia Commonwealth University, USA.
• Objective: Studied the impact of discrimination and stigma on mental health outcomes in transgender individuals.
• Findings:
• Gender-related discrimination is the strongest risk factor for poor mental health in transgender people.
• Higher rates of depression, anxiety, and suicidality were associated with social rejection and discrimination.
• Significance: Demonstrates that restrictive policies and societal stigma harm transgender individuals, emphasizing the need for legal and social protections.
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- Mezza et al. (2024) – Protective Factors for Transgender Well-Being
• Location: Conducted at Sapienza University of Rome, Italy.
• Objective: Investigated factors that promote resilience and mental health among transgender individuals.
• Findings:
• Self-esteem, pride, and social support significantly improve mental health.
• Transitioning (social or medical) improves quality of life and reduces mental health risks.
• Significance: Supports affirming transgender identities as a public health necessity, countering arguments that transition-related care is unnecessary or harmful.
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- Witten (2003) – Long-Term Well-Being of Transgender Individuals
• Location: Conducted at Texas A&M University, USA.
• Objective: Studied long-term mental and physical health outcomes of transgender individuals who received affirming care.
• Findings:
• Respecting and affirming gender identity improves psychological resilience and life satisfaction.
• Lack of acceptance leads to worse long-term mental health outcomes.
• Significance: Reinforces that affirmation and support—not restrictions—lead to better mental health outcomes for transgender individuals.
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Conclusion
• Neuroimaging studies (Mueller et al., Nguyen et al.) show biological differences in transgender individuals’ brains, supporting gender identity as a neurodevelopmental trait.
• Sociological and psychological studies (Bradford et al., Mezza et al., Witten) confirm that discrimination harms transgender individuals, while affirmation promotes mental health.
• Historical and cultural research (Gill-Peterson) refutes the claim that non-binary identities are a modern social construct.
• Medical research (Esteban et al.) confirms that sex is not strictly binary, as 1.7% of the population has variations in sex development (DSD/VSC).
These findings disprove binary sex-based policies and support affirming gender identity in medical, psychological, and legal frameworks).
Brain Sex in Transgender Women Is Shifted towards Gender Identity - National Library of Medicine; 2022
Study Breakdown: Neuroanatomy of Transgender Women Before Hormone Therapy
Research Conducted At:
• University of California, Los Angeles (UCLA), USA
• University of Auckland, New Zealand
Objective
• Investigate whether the brain structures of transgender women (assigned male at birth but identifying as female) resemble cisgender men or cisgender women before hormone therapy.
• Use a multivariate machine learning classifier to analyze brain structure in a continuous (non-binary) spectrum rather than a strict male/female classification.
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Participants
• Total Sample: 72 adults
• 24 cisgender men (biological males, identify as male)
• 24 cisgender women (biological females, identify as female)
• 24 transgender women (biological males, identify as female, pre-hormone therapy)
• Mean Age: ~45.7 years (range: 23–72 years)
• Sexual Orientation of Transgender Women in Study:
• 6 were androphilic (attracted to men)
• 18 were gynephilic (attracted to women)
• All transgender women were confirmed genetically male (SRY gene present).
• Cisgender participants were selected from the International Consortium for Brain Mapping (ICBM) database.
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Methodology
MRI Scanning & Brain Processing
• MRI Scanner: Siemens Sonata (1.5 Tesla)
• Imaging Parameters:
• 160 sagittal slices
• Voxel size: 1.0 × 1.0 × 1.0 mm³
• Processing Software:
• SPM8 & VBM8 Toolbox for brain segmentation
• PCA (Principal Component Analysis) for data reduction
• Machine learning-based Brain Sex Classifier
• Independent Training Sample:
• Data from 547 adults (305 females, 242 males) aged 19–86 (IXI database)
• Used for classifier training
Brain Sex Estimation
• Machine Learning Model: Relevance Vector Regression (RVR) Machine
• Brain sex assigned on a continuous scale:
• 0 = female-typical brain
• 1 = male-typical brain
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Results
• Classifier Accuracy:
• 90.2% in training sample
• 88.3% in cisgender validation sample
• Brain Sex Scores:
• Cisgender Men: 1.00 ± 0.41
• Cisgender Women: 0.00 ± 0.41
• Transgender Women (Pre-Hormone Therapy): 0.75 ± 0.39
• Significantly different from cisgender men (p = 0.016, Cohen’s d = 0.64)
• Significantly different from cisgender women (p < 0.001, Cohen’s d = 1.87)
• Key Finding: Transgender women’s brains shifted away from male-typical structure toward female-typical, but were not identical to cisgender female brains.
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Discussion & Implications
• Supports the idea that brain structure differences contribute to gender identity.
• Transgender women’s brain anatomy is not fully male-typical even before hormone therapy.
• Aligns with previous research:
• Studies on brain sex classification accuracy in transgender individuals
• Findings of sex-atypical regions like the INAH-3, insula, bed nucleus of the stria terminalis (BSTc), and posterior cingulate
Limitations & Future Research Recommendations
• Sample size was relatively small (n = 24 per group).
• Future studies should analyze transgender men as well.
• Sexual orientation should be accounted for in future studies, as it also affects brain anatomy.
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Key Takeaways
• Transgender women’s brain structures are not fully male-typical, even before hormone therapy.
• Their brains exhibit a shift toward female-typical structures, though they remain distinct from both cisgender men and cisgender women.
• Supports a neurobiological basis for gender identity, challenging arguments that gender identity is purely a social construct.
• Future research with larger samples and additional transgender groups is needed.
Structural connections in the brain in relation to gender identity and sexual orientation - Nature; 2017
Study Breakdown: Structural Connections in the Brain in Relation to Gender Identity and Sexual Orientation
Research Conducted At:
• Karolinska Institute, Sweden
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Objective
• Investigate brain structure differences in transgender individuals and homosexual individuals using Fractional Anisotropy (FA), a measure of white matter connectivity that shows known sex differences.
• Determine if transgender people’s brain structures align with their assigned sex at birth or their gender identity.
• Compare these findings to differences observed in homosexual cisgender individuals to differentiate between the neurobiological bases of gender identity and sexual orientation.
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Participants
• Total Sample: 206 adults
• 40 transgender men (female at birth, identify as male)
• 27 transgender women (male at birth, identify as female)
• 29 cisgender homosexual men
• 30 cisgender homosexual women
• 40 cisgender heterosexual men
• 40 cisgender heterosexual women
• Mean Age Ranges: 24–30 years
• Sexual Orientation of Transgender Participants:
• Transgender Men (TrM):
• 60% attracted to women (gynephilic)
• 20% bisexual
• 12.5% attracted to men (androphilic)
• Transgender Women (TrW):
• 55.5% attracted to men (androphilic)
• 33.3% attracted to women (gynephilic)
• 3.7% bisexual
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Methodology
Brain Imaging Approach
• MRI Technique: Diffusion Tensor Imaging (DTI)
• Key Measurement: Fractional Anisotropy (FA)
• Higher FA = More organized and myelinated white matter fibers
• FA values typically higher in men than in women in major brain pathways
• Brain Regions of Interest:
• Superior Longitudinal Fasciculus (SLF) → Important for cognitive processing
• Inferior Longitudinal Fasciculus (ILF) → Connects occipital and temporal lobes
• Corticospinal Tract (CST) → Involved in movement
• Corpus Callosum (CC) → Connects brain hemispheres
• Inferior Fronto-Occipital Fasciculus (IFOF) → Plays a role in body perception
• Statistical Analysis:
• Compared FA values across all groups
• Controlled for age and sexual orientation
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Results
- Differences in White Matter by Sex (Cisgender Heterosexual Groups)
• Cisgender heterosexual men had significantly higher FA values than cisgender heterosexual women in several brain pathways.
• FA differences between cisgender homosexual men and women were smaller, meaning homosexual individuals had less pronounced sexual differentiation in white matter structure. - Transgender Participants & Gender Identity
• Most FA values in transgender individuals followed their assigned sex at birth.
• Exception: The right inferior fronto-occipital fasciculus (IFOF) showed a sex-atypical pattern, meaning FA values aligned more with gender identity rather than birth sex.
• This region is responsible for processing self-perception and body ownership. - Homosexuality vs. Gender Identity Differences
• Homosexual individuals did not show major FA differences compared to their heterosexual counterparts, except for some mild decreased sexual differentiation.
• Transgender individuals, however, showed distinct differences in the IFOF, which were not present in homosexual individuals.
• This suggests that gender identity and sexual orientation have different neurobiological underpinnings.
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Key Conclusions
• Gender dysphoria is linked to brain areas responsible for self-perception and body ownership (IFOF).
• Transgender individuals’ brain structures do not simply match their assigned sex or gender identity fully, but the right IFOF is a key marker of gender incongruence.
• Homosexuality appears to be associated with a less pronounced male-female brain differentiation rather than a fundamental shift in brain structure.
• This study supports the theory that transgender identity is rooted in neurobiology, particularly in the way the brain processes self-perception and body ownership.
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Implications for Future Research
• Future studies should examine larger transgender samples and longitudinal changes with hormone therapy.
• More research is needed to explore why the IFOF is involved in gender identity and not sexual orientation.
• Findings could help improve psychological and medical support for transgender individuals by recognizing that their gender identity has measurable brain differences.
What has sex got to do with it? The role of hormones in the transgender brain - National Library of Medicine; 2018
This study provides an extensive review of the effects of gender-affirming hormone therapy (GAHT) on brain structure, function, and cognitive abilities in transgender individuals. It explores both baseline neurological differences in transgender individuals before GAHT and how GAHT influences brain morphology, cognition, and mental health over time.
Key Findings and Themes:
1. Brain as a Gender Mosaic:
• The study challenges the binary view of the brain and presents evidence that both male and female characteristics exist in all brains to varying degrees.
• It suggests that gender identity may arise from a mismatch between brain development and assigned sex at birth.
2. Baseline Differences in Transgender Brains (Before GAHT):
• Some neuroimaging studies show that brain structures and cognitive function in transgender individuals align more with their gender identity rather than their natal sex.
• However, conflicting studies suggest that certain brain structures may still align with natal sex, leading to the conclusion that gender identity exists along a spectrum rather than a strict binary.
3. Effects of GAHT on Brain Structure:
• For MTF individuals (male-to-female): Estrogen and anti-androgen therapy decreases brain volume, particularly in areas like the hippocampus, and shifts certain brain structures toward a more typically female pattern.
• For FTM individuals (female-to-male): Testosterone therapy increases brain volume and enhances white matter connectivity, leading to masculinization of certain brain structures.
• These changes suggest hormonal treatment has a direct impact on brain plasticity, but more research is needed on long-term effects.
4. Effects of GAHT on Cognitive Performance:
• MTFs experience a decline in spatial abilities (typically male-biased) and an increase in verbal fluency (typically female-biased) after estrogen therapy.
• FTMs show an increase in spatial ability (typically male-biased) but a decline in verbal fluency (typically female-biased) after testosterone therapy.
• These findings support the idea that hormones actively shape cognitive function in adulthood.
5. Mental Health and Behavioral Effects of GAHT:
• GAHT is linked to improvements in gender dysphoria, body satisfaction, and psychological well-being.
• However, testosterone in FTMs may increase aggression, irritability, and impulsivity, whereas MTFs on estrogen show reductions in aggression and sexual arousal.
• While GAHT is associated with better mental health outcomes, transgender individuals still experience higher rates of anxiety and depression compared to cisgender individuals.
6. Gaps in Research and Future Directions:
• Long-term safety of GAHT on brain health is largely unknown. Most studies are short-term (≤18 months) and lack randomized controlled trials.
• There is a lack of studies on non-binary and gender-fluid individuals. Research has focused mainly on MTFs, leaving transmasculine individuals underrepresented.
• Studies should focus less on binary sex differences and more on executive function, memory, and emotional regulation, which are crucial for daily life.
• GAHT’s potential effects on cognitive decline and neurodegenerative diseases later in life need investigation.
Overall Takeaway:
This review highlights that gender-affirming hormone therapy significantly impacts brain structure, cognitive function, and mental health, often aligning transgender individuals’ neurological traits more closely with their gender identity. However, long-term effects remain poorly understood, and more rigorous research is needed to ensure the safest and most effective treatment approaches.
Transgender Trend; The ‘Pink and Blue Brain’ Myth
Here are the key points from the Transgender Trend article “The ‘Pink and Blue Brain’ Myth”:
1. No Binary Brain Structure – The article argues that brains are not strictly male or female but exist as a mosaic of traits influenced by genetics, hormones, and environment.
2. Brain Plasticity – Children’s brains are highly adaptable and shaped by experiences rather than being hardwired at birth with a specific gender identity.
3. No ‘Gender Identity’ Brain Region – There is no scientific evidence supporting the existence of a specific brain area that determines gender identity.
4. Neuroscience and Misinterpretation – While some studies suggest minor sex-based differences in brain structures, they do not prove an inherent “gender identity” or a strict male/female division.
5. Role of Socialization – The article emphasizes that social and cultural influences play a significant role in shaping behaviors and perceptions of gender.
6. Challenges to ‘Born This Way’ Narrative – It questions claims that transgender identity is biologically predetermined, arguing that such claims lack strong scientific backing.
7. Concerns About Medicalization – The article warns against using neuroscience to justify early medical interventions, emphasizing the need for a more cautious approach.
The overall argument is that gender identity is not biologically fixed at birth but is influenced by a combination of biological, psychological, and social factors.
Structural, Functional, and Metabolic Brain Differences as a Function of Gender Identity or Sexual Orientation: A Systematic Review of the Human Neuroimaging Literature - National Library of Medicine; 2021
The study titled “Structural, Functional, and Metabolic Brain Differences as a Function of Gender Identity or Sexual Orientation: A Systematic Review of the Human Neuroimaging Literature” systematically reviewed existing neuroimaging research to explore potential brain differences associated with gender identity and sexual orientation. 
Key Findings:
• Gender Identity: The review analyzed 39 studies comparing cisgender and transgender individuals before hormonal treatment. While most neuroanatomical, neurophysiological, and neurometabolic features in transgender individuals aligned with their natal sex, certain brain characteristics resembled those of their experienced gender. 
• Sexual Orientation: Among 24 studies comparing heterosexual and homosexual individuals, findings indicated that the majority of brain features in homosexual individuals were similar to those of heterosexuals of the same sex. However, some brain characteristics in homosexual individuals mirrored those typically observed in heterosexuals of the opposite sex. 
Study Limitations:
The review highlighted several challenges in drawing definitive conclusions: 
• Sample Size: Many studies had small to moderate sample sizes, limiting the generalizability of findings. 
• Methodological Variability: Differences in neuroimaging techniques and study designs contributed to inconsistent results across studies. 
• Conflicting Results: Variations in findings made it difficult to identify specific brain features consistently differing between groups. 
Conclusions:
The authors emphasized that, while some brain features in transgender and homosexual individuals differ from those in cisgender and heterosexual populations, respectively, the majority align with their natal sex or same-sex heterosexual counterparts. They noted that current neuroimaging tools might not detect subtle differences contributing to gender identity and sexual orientation. The study calls for further research with larger sample sizes and standardized methodologies to enhance understanding of the neurological substrates of human sexuality. 
