Gender

Introduction & Lecture Scope

• New lecture for $2023$ focusing on biological contributions to gender-identity development.
• Content is NOT examinable this year but revisits earlier, examinable, concepts (sexual differentiation, sex vs gender).
• Lecturer invites feedback; material is a work-in-progress and cannot cover every aspect.

Core Definitions & Terminology

• Sex (biological): Cluster of physical attributes (chromosomes, genes, hormones, internal & external reproductive organs).
• Gender: Socially/culturally determined traits, characteristics, expectations of “masculine” or “feminine.” Varies by culture.
• Gender Identity: Innermost sense of self as male, female, both, or neither; may align with or differ from sex assigned at birth.
• Cisgender: Gender identity aligns with birth sex.
• Transgender: Gender identity opposite to birth-assigned sex.
• Gender Expression: Outward representation (clothing, hairstyle, language, behaviour). Can be constrained by culture (e.g., Australian school-uniform rules; lecturer’s own preference for trousers despite being cis-female).
• Sexual Orientation: Pattern of physical/romantic attraction (heterosexual, gay, lesbian, bisexual, pansexual, demisexual, asexual, etc.). Distinct from gender identity.

Multidimensionality & Intersectionality

• Gender identity and sexual orientation intersect but are independent dimensions.
  • Example: A person identifying as gay (orientation) can be cis-man, cis-woman, trans-man, trans-woman or non-binary.
  • Conversely, a non-binary individual might identify as lesbian, gay, bisexual, pansexual, queer, asexual, or other.
• Intersections are shaped by social/political context, life stage, and personal circumstances.

Rationale for Biological Investigation

• Marked sex differences: majority of genetic females identify as female & are attracted to males; majority of genetic males identify as male & attracted to females.
  • “Majority” ≠ “normal”; biology exists on a spectrum.
• Dramatic differences suggest biological components—particularly gonadal hormones (testosterone) that also drive sex-organ formation.
• Lecture roadmap:
  1. Animal evidence for hormonal programming of brain.
  2. Clinical/"natural" human studies.
  3. Acknowledgement of learning & socialisation interactions.

Review: Sexual Differentiation of the Genitals

• Fertilisation by X or Y sperm determines chromosomal complement.
  • XY → SRY gene on Y → indifferent gonad → testes → testosterone → Wolffian duct develops (epididymis, vas deferens, seminal vesicle) & external genitalia (scrotum, penis).
  • XX → No SRY → indifferent gonad → ovaries → no testosterone or AMH → Müllerian duct develops (uterine tube, uterus, upper vagina) & female external genitalia (clitoris, labia).

Organisational–Activational Theory of Brain Sexual Differentiation

• Prenatal/neonatal testosterone during a critical window organises (permanently masculinises) neural circuits.
• Later pubertal/adult gonadal hormones activate behaviours on this pre-wired substrate.
• Critical periods = late fetal or early neonatal life when brain is highly hormone-sensitive.

Animal Evidence

• Rats: males mount; females show lordosis.
  • Exposure of neonatal females to testosterone/estradiol (first $5$ days) → defeminisation & mounting in adulthood.
• Convenience of rat model: critical window occurs post-natally → precise experimental control.
• Cross-species consistency (play, mating, parental behaviours) underpins hypothesis that human brains are also hormone-programmed.

Timing of Testosterone Peaks in Humans

• Fetal males have elevated testosterone from about week $8$–$20$ gestation (reaching near-adult concentrations) then decline toward birth.
• Mini-puberty: $1^{st}$–$3^{rd}$ post-natal months—male infants’ testosterone again rises to pubertal levels.
• Elevated male:female ratios during both windows presumed to program brain morphology/function via epigenetic mechanisms.

Beyond Hormones: Chromosomal & Genetic Inputs

• Four-core-genotype mouse model: SRY removed from Y & inserted onto autosome → yields XX/XY mice with either testes or ovaries.
  • Reveals sex-chromosome effects on play, mating, parental care, learning.
  • Some behaviours require Y chromosome; others modulated by number of X chromosomes.
• Human MRI studies of sex-chromosome aneuploidies show structural brain differences correlated with X-chromosome number, but functional meaning unclear.

Methodological Constraints in Humans

• Ethical barriers preclude experimental hormone manipulation.
• Reliance on “natural experiments”: rare genetic variants of hormone enzymes/receptors, intersex conditions, and self-identified transgender populations.
• Need to disentangle early-hormone, chromosomal, adult-hormone, and social-learning effects—very challenging.

Clinical “Natural Experiments” Involving Early Androgen Variation

Classical Congenital Adrenal Hyperplasia (CAH)

• Mutation of $21$-hydroxylase → cortisol deficiency → excess androgen production.
• XX females: varying external masculinisation.
• Findings:
  • Childhood: prefer “boys’” toys (trains, cars), rough-and-tumble play.
  • Less responsive to parental gender-typing cues ("doll for girls," etc.).
  • Adulthood: weaker female gender identity strength & higher prevalence of bisexual orientation, yet most still identify as women.
• XY males with CAH: androgen levels within male range; less studied.

Complete Androgen Insensitivity Syndrome (CAIS)

• XY with non-functional androgen receptors → testes present but body can’t respond to androgens → typically female external genitalia.
• Behaviour/identity: majority show female-typical childhood behaviour & identify as women; small minority report other identities.
• Supports idea that absence of androgen signalling → female-typical psychosexual outcome.

$5\alpha$-Reductase Deficiency

• Cannot convert testosterone → $5\alpha$-DHT (crucial for external masculinisation).
• XY individuals born with ambiguous/female-appearing genitalia; puberty testosterone surge enlarges penis/scrotum, virilises body.
• Dominican Republic “guevedoces” incidence $\approx 1/90$: raised as girls, transition socially to boys at puberty; majority ultimately identify as male.

David Reimer Case Study

• Circumcision accident destroyed penis; reassigned female surgically before $2$ yrs.
• Raised female; discovered history in teens, re-transitioned to male; lived as man until death at $38$.
• Demonstrates strong impact of prenatal/early androgen exposure despite socialisation as female.

Synthesis of Clinical Evidence

• Early androgen exposure exerts measurable, often enduring influence on gender role behaviours & identity.
• Lack of androgens tends toward female-typical outcomes; excess tends toward male-typical outcomes.
• “Most” ≠ “all” → biology influences probability, not destiny.

Genetic Studies in Transgender Populations

• Family & twin data: higher within-family concordance than general population, especially among monozygotic twins, but sample sizes small & dated.
• Candidate-gene work (receptors, enzymes) yields mixed or conflicting associations; functional implications of polymorphisms poorly understood.
• Rising societal acceptance may inflate apparent familial clustering via openness rather than heredity.

Neuroanatomical Imaging Findings

• MRI comparisons: some structural/functional features in transgender people align more closely with cis individuals sharing the same gender identity rather than the same biological sex.
• Replication inconsistent; causality unknown (early hormones vs lived experience vs methodological artefacts).
• Reminder: correlation ≠ causation; brain differences might reflect shared lifestyle factors.

Limitations & Research Gaps

• No single biological factor explains all gender diversity.
• Complex interactions between genes, prenatal hormones, post-natal hormones, and socialisation remain unresolved.
• Studies often rely on rare conditions (small N) or clinic-referred samples (selection bias).
• Under-representation of non-binary identities, racial & cultural diversity.

Ethical, Philosophical & Practical Implications

• Biological evidence counters claims that gender diversity is “unnatural,” but can be politicised to:
  • Support acceptance or
  • Pathologise diversity via search for “biomarkers” & early “interventions.”
• Trans & gender-diverse people frequently identified as non-conforming early → stigma → mental-health burden.
• Tackling stigma, rigid norms, and embracing diversity is critical for wellbeing.

Key Statistics on Youth Health & Mental Health (Australian LGBTQA+ study, $\approx$ $6\,000$ respondents)

• Self-rated general health:
  • Poor/Fair: $35\%$ vs $9\%$ in general population.
  • Very good/Excellent: $27.7\%$ vs $63\%$ general population.
• Mental-health disparities for trans & gender-diverse (TGD) youth:
  • High/very-high psychological distress in past month: $3$ × more likely.
  • Considered suicide (past $12$ mo): $5$ × more likely.
  • Attempted suicide (past $12$ mo): $3$ × more likely.

Recommendations for Improving Outcomes

• Reduce homophobia, biphobia, transphobia at societal & institutional levels.
• Challenge rigid gender stereotypes; provide supportive environments (e.g., flexible school-uniform policies).
• Celebrate and normalise diversity to improve mental-health metrics.

Further Resources & Next Steps

• Lecturer provides curated list of ABC iView videos with lived-experience narratives (links not transcribed here).
• Students encouraged to review previous semester materials on sexual differentiation for exam preparation.
• Feedback on lecture content and desired future depth is welcome.