Biological Basis of Gender PSYC101 Prof. Gregg Fall, 2007
Background: Sociobiology • Evolution suited men to struggle for power & run society; women to raise babies & nurture • Men evolved to spread sperm widely; seek physically attractive & healthy partners • Women evolved to nest; seek provider-protectors Don’t mess with biology Socialization should affirm biology
Background:Cultural Determinism • Great cultural variation in gender roles shows plasticity of human nature • Our gender roles are cultural constructions: masculinity & femininity are performances • Socialization should be non-gender based, or encourage androgyny
Psychology Research:“Sex Typing” of Behavior • Individual differences: • Prominent & rigid gender schemas vs. • “a-schematic” or “androgynous” • Historical change from 1940s: • From rigid toward flexible • or: from clear toward ambiguous
Essentialists vs. Constructivists • Essentialism: • Gender differences are biological • Advocates of difference • Constructvism: • Gender differences are cultural • Advocates of sameness
Difference vs. Sameness Advocates of difference: • Innate differences need parental & cultural support • Guide male / female complementarity Advocates of sameness: • Raise girls & boys same • Allow temperaments to be expressed
Biological Bases of Gender • John Money: Sexual Signatures • John Pinel: Biopsychology • Colapinto: Joan / John Case?
Components of Gender 1. Gender identity 2. Gender role behaviors 3. Sexual orientation
Key Processes • Hormonal influences on bodies & brains • Neuro-endocrine axis: hypothalamus – pituitary – gonads • Critical stages: “gates” • Non-normal development
Adam Principle • Default development of both XY and XX: female! • Something must be added – mostly androgens – to get a “male.”
Non-“normal” development • Johns Hopkins Gender Clinic (J. Money) • Intersexes (hermaphrodites) • homosexuals • transvestites • transexuals • Genetics & hormones not in synch • genetic males + no androgens (insensitivity) • genetic females + androgens (adrenogenital)
Three Cases • Joan / John case: raised as a girl • Chose to become boy • Biology or rearing? • 12 yr old XX adreno-genital raised as boy • Chose to become girl • 11 yr old XX adreno-genital raised as girl • Chose to become boy
John Money’s Theory • Role behaviors mainly nature • Sex orientation mainly nature • Gender identity mainly nurture • Identity “Gate” remains open until language, then closes
Mystery Why does gender identity sometimes develop contrary to nature & rearing?
“Adam Principle” • “Nature’s impulse is to create a female” • “Default” development – no androgens female body and brain (estrogens required at puberty)
Neuron Basics About 100 billion of ’em About 100 trillion connections
Resting Potential-70 mvsodium, chlorine & potassium move across cell membrane, through ion channels
“Firing” of Neuron Neurotransmitter binds to protein on dendrite, and either… Fast: opens ion channel (Na+ ions flow in), triggering shift in potential or… Slow: triggers series of reactions that may open ion channels -- and also change cell metabolism and/or gene expression.
Potassium channels open restores - charge Sodium channels open charge becomes + “Firing” of Neuron
Psychoactive Drugs • Chlorpromazine: anti-schizophrenic, blocks dopamine receptors • Valium: blocks one type of GABA receptor, causing increased GABA binding at others • Prozac: anti-depressant, blocks re-uptake of serotonin (prolonging its action in synapse)
Biology of Gender Development • Controlled by neuro-hormonal feedback system • Hypothalamus -- pituitary gland – testes • Critical stages in development • Non-normal development
Hormones • Androgen:any substance that promotes development or function of male reproductive system (mainly synthesized by testes, but small amounts synthesized by adrenal gland and by ovaries) • Estrogen & progestins: substances that stimulate the maturation or function of female reproductive system (mainly synthesized by ovaries, but small amounts synthesized by adrenal gland and testes)
Hormones • Everyone has both androgens & estrogens • Males: mainly androgens • Females: mainly estrogens • Estrogen may play imp’t role in male development • Androgen may play imp’t role in female development
Anatomy Hypothalamus Pituitary Gonad axis
Gonads • Testes in men • Ovaries in women
Pituitary Gland • “Master gland” • Produces hormones that regulate synthesis and release of other hormones from thyroid, adrenal gland, testes & ovaries, etc. • Gonadotropins: cause testes or ovaries to produce and release androgens and estrogens
Pituitary • Cyclical release of gonadotropins in females • Menstrual cycle • Sexual activity in animals • Steady release of gonadotropins in males
Pituitary • Sexually dimorphic? • 1952 study: cycling female rat pituitary transplanted into male stops cycling; steady-state male rat pituitary transplanted into female begins cycling • Pituitary not sexually dimorphic
Origin of Sexual Dimorphism? • Animals that breed seasonally influenced by light • Birds taken across equator reverse seasons of breeding • Whatever controls pituitary influenced by optical information Hypothalamus?
Hypothalamus • Composed of various nuclei, which produce different releasing and inhibiting hormones • Regulate 4 F’s: feeding, fighting, fleeing & mating • Also: body temperature, thirst, sleep, stress response
Hypothalamus • Electrical stimulation and lesions in hypothalamus affect pituitary’s production & release of hormones • 1960s: thyrotropin-releasing hormone identified in pig hypothalamus – influences pituitary function • Thyrotropin-releasing hormone produced in hypothalamus, transported to pituitary
Hypothalamus Might the hypothalamus be sexually di-morphic?
Hypothalamus • 1970s: gonadotropin releasing hormone identified in hypothalamus • Causes pituitary to release gonadotropins • Evidence for sexual dimorphism
Hypothalamus – • pituitary • connections • Neurohormonal • nerve cells
Hypothalamus - Pituitary • 9 neurohormones secreted or transported from hypothalamus to pituitary by nerve cells and capillary system • Control release of sexual hormones, growth hormones (from thyroid), endorphins, and others.
Hypothalamus – PituitaryGonadotrohpins • FSH: Follicle-stimulating hormone sperm production in men mature germ cells in women • LH: Lutinizing hormone release of androgens from testes release of estrogens from ovaries
Feedback System • Hypothalamus – pituitary – gonads • Hormones released in pulses relatively large doses over minutes several times a day • Hormone levels fluctuate during day • “Gonadostat” adjusting hormones in hyhpothalamus
Feedback circuit: Hypothalamus Pituitary Gonads