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 providerprotectors
 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
– genetic females + androgens
(insensitivity)
(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?
Neuro-endocrinology
of
Gender Development
“Adam Principle”
• “Nature’s impulse is to create a female”
• “Default” development – no androgens
 female body and brain
(estrogens required at puberty)
Brain Basics
Neuron Basics
About 100 billion of ’em
About 100 trillion connections
Neuron
Axon Button
Resting
Potential
-70 mv
sodium, 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.
Sodium channels open
charge becomes +
Potassium channels open
restores - charge
“Firing” of Neuron
“Firing” of Neuron
Neuron
“Firing”:
neurotransmitter
release
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 reuptake 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
Primary glands
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 Gland
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
Hypothalamus
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
1. Neurohormonal
nerve cells
Hypothalamus – Pituitary
2. capillary portal system
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 – Pituitary
Gonadotrohpins
• 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
Role of Circulating Hormones
• Does mix of circulating hormones explain
behavioral differences between men &
women?
• Aggression, assertiveness, mathematical
vs. verbal abilities, nesting / homemaking
talents, etc.
• Evidence suggests No
(mostly)
Circulating Hormones
• Sex interest & aggression in men
little influenced by testosterone
levels
(no testosterone reduces both;
high doses of androgens may increase
both)
Circulating Hormones
• Sex interest & aggression in women
unrelated to estrogen levels – or
menstrual cycles
(But: female sexuality may be influenced
by small amounts of androgens, and male
sexuality by small amounts of estrogens)
Pre-natal hormone exposure
• Differentiates male & female
organizations of hypothalamus
• Cyclical (female) vs. steady-state (male)
• Aggression – “rough & tumble play”?
• Spatial vs. verbal abilities?
• Sexual orientation?
• Gender identity?
Pre-natal hormone exposure
• Androgens  “male” hypothalamus?
• No androgens  “female” hypothalamus?
Other Dimorphic Structures?
• corpus callosum?
• Thalamus
• limbic system (emotion)
Limbic
System
Limbic
System
Dimorphic brain structures
• Androgen exposure at critical pre-natal
periods may virilize brain structures &
hormone regulation
• Absence of androgen exposure may
feminize brain structures & hormone
regulation
Pre-natal androgen exposure
• Evidence from non-primates (rats),
primates (apes & monkeys) & humans:
– more aggression / fighting;
fewer signs of deference
– preference for more “rough and tumble” play;
less nesting / mothering play
– greater spatial ability; lower verbal ability
– sexual behavior: mounting (more “male”?)
Pre-natal androgen exposure
• Influences average differences between
males & females
• Influences differences among males &
among females
Androgen Exposure Theory
• More androgens  more “masculine”
males;
• Less androgens or insensitivity  more
“feminine” males, & perhaps greater
bisexual or homosexual orientation
• More androgens  more “masculine”
females, and perhaps bisexual or
homosexual orientation.
Androgen Exposure – but:
• It may be estradiol that “masculinizes”
• Synthesized from androgens (by addition of
benzene ring)
Pre-Natal Stages
of Gender Development
“Adam Principle”
• “Nature’s impulse is to create a female”
• “Default” development – no androgens
 female body and brain
(estrogens required at puberty)
Normal bodily development
• Undifferentiated Stage – first 6 weeks
• “anlagen” (precursors) that will become
M & F organs
– Gonads  testes or ovaries
– Genital tubercule  penis or clitoris
– Wolffian ducts  male structures
– Mullerian ducts  female structures
Gonadal differentiation
• Week 7
• Y chromosome triggers TDF – testes
determining factor
• Gonads organize as testes, begin
producing androgens
• ONLY direct genetic influence
Androgen effects – weeks 7 - 10
• Stimulate Wolffian ducts to develop as
seminal vesicules, prostate, etc.
• Testes release MIS (Mullerian-inhibiting
substance)  withering of Mullerian
ducts
• Genital tubercule begins to develop as
penis
Androgen effects – weeks 7-???
“Virilize” hypothalamus:
• Suppresses cyclic hormonal regulation
• Organizes to trigger pituitary release of
masculinizing hormones at puberty
• Influences behavioral inclinations?
• Influences sexual orientation?
No Androgens -- weeks 7 to 13
• “Default” differentiation of female
reproductive organs
– Mullerian ducts begin organizing as ovaries
– Wolffian ducts wither
– Genital tubercule organizes as clitoris &
labia
• Requires absence of androgens, not
presence of estrogens
No Androgens – weeks 7 to 13
• Estrogen may “virilize” genetic female
• Females protected from mother’s
estrogens by placental barrier
• Synthetic estrogens cross barrier, as do
androgens from adrenal gland
• Like adrenal androgens, D.E.S.
“virilizes”
Puberty
• “Gonadostat” in hypothalamus resets to
release LSH and LH, triggering puberty
• Androgen release  male characteristics
(muscle growth, facial hair, voice, etc.)
• Estrogen release  female characteristics
(breast development, menstruation, etc.)
Gender Role Behavior &
Sexual Orientation
Animal Experiments
• Rats (peri-natal critical period):
– Females given testosterone  less
lordosis (receptivity to mounting), more
mounting
– Males castrated  less mounting
– Given estrogens later  show lordosis
Animal Experiments
• Primates:
– Similar effects on sexual behavior
– Androgens  more “rough & tumble play”
 less maternal care-taking
Hypothalamus & sexual orientation
Sexual Orientation & Roles
• Gay men: “masculine” & “feminine”
• Lesbians: “masculine” & “feminine”
• Bisexuals: “masculine” & “feminine”
(So-called) “Normal” development
• Concordance of:
– Genetic sex
– Gender identity
– Gender role behaviors
– Preponderant sexual orientation
Non- “normal” Development
Androgen insensitivity:
• XY follows female path of body and
brain development
Adreno-genital syndrome:
• XX exposed to androgens produced by
adrenal cortex  body and perhaps
brain partially “virilized”
Non- “normal” Development
Exogenous estrogen exposure:
• D.E.S. (synthetic hormone used to
prevent miscarriage)  “virilize” XX
gender behaviors & increase bisexuality
5 -reductase syndrome:
• partial androgen insensitivity; XY
usually raised as girls, but androgens at
puberty masculinize
5 -Reductase Syndrome
• Dominican Republic:
18 of 33 raised as girls
When puberty masculinized, most became
male, but some remained “women”
• New Guinea:
5 of 14 raised as girls
When puberty masculinized, all became male
(with much “social trauma”)
• “Gender Identity Gate” remains open?
Cases
• Some cases support theory that gender
identity determined by rearing
• But some suggest there’s a sense of
maleness or femaleness independent of
rearing
• 5 -reductase cases suggest “gate”
may not close around age of 3
“Take Home” Points
• Hypothalamus – pituitary – gonadal axis
• Adam Principle
• Gender dimorphism of hypothalamus
• Gender role behaviors influenced mainly by prenatal hormones, not circulating hormones
• Influence on: rough & tumble play; nesting &
care-taking; visual & spatial abilities; sexual
orientation
“Take Home” Points -- 2
• Critical periods in gender development
• Non- “normal” syndromes
– XX “virilized” by androgens (adrenal
cortex)
– XY “feminized” by androgen insensitivity
• GENDER IDENTITY / ROLE BEHAVIORS /
SEXUAL ORIENTATION:
– Different components of gender
– May be not in synchrony
“Take Home” Points -- 3
• Money’s “gender identity gate” theory
– Open to rearing until 2 or 3
– Make early gender assignment
– Now generally rejected
• Gender clearly isn’t all NURTURE
but also clearly isn’t all NATURE
• Contemporary treatment strategies
– Delay surgery
– Raise with provisional gender identity
“Take Home” Points -- 4
Gender Identity: don’t know cause
likely prenatal hormone influence
rearing likely strong influence
many cases have no clear explanation
“Take Home” Points -- 5
• Gender Role Behaviors: mix & timing
of “virilizing” prenatal hormones
male – female differences
variation among men & among women
strong role of environment
(historical change & cultural variation)
“Take Home” Points -- 6
• Sexual Orientation: likely prenatal
hormone influence on homosexual vs.
heterosexual orientation
Also environmental influence (Sambia)
transvestism & transexualism remain
mysteries
Some Questions
• Role of culture:
–Affirm biology?
–Amplify biology?
–Modify biology?