Biological Basis of Gender

Presentation on theme: "Biological Basis of Gender"— Presentation transcript:

1 Biological Basis of Gender
PSYC101 Prof. Gregg Fall, 2007

2

3 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

4 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

5 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

6 Essentialists vs. Constructivists
Essentialism: Gender differences are biological Advocates of difference Constructvism: Gender differences are cultural Advocates of sameness

7 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

8 Biological Bases of Gender
John Money: Sexual Signatures John Pinel: Biopsychology Colapinto: Joan / John Case?

9 Components of Gender 1. Gender identity 2. Gender role behaviors
3. Sexual orientation

10 Key Processes Hormonal influences on bodies & brains
Neuro-endocrine axis: hypothalamus – pituitary – gonads Critical stages: “gates” Non-normal development

11 Adam Principle Default development of both XY and XX: female!
Something must be added – mostly androgens – to get a “male.”

12 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)

13 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

14 John Money’s Theory Role behaviors  mainly nature
Sex orientation  mainly nature Gender identity  mainly nurture Identity “Gate” remains open until language, then closes

15 Mystery Why does gender identity sometimes develop contrary to nature & rearing?

16 Neuro-endocrinology of Gender Development

17 “Adam Principle” “Nature’s impulse is to create a female”
“Default” development – no androgens  female body and brain (estrogens required at puberty)

18 Brain Basics

19 Neuron Basics About 100 billion of ’em About 100 trillion connections

20 Neuron

21 Axon Button

22 Resting Potential -70 mv sodium, chlorine & potassium move across cell membrane, through ion channels

23 “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.

24 “Firing” of Neuron Potassium channels open Sodium channels open
charge becomes + Potassium channels open restores - charge “Firing” of Neuron

25 “Firing” of Neuron

26 Neuron “Firing”: neuro- transmitter release

27 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)

28 Biology of Gender Development
Controlled by neuro-hormonal feedback system Hypothalamus -- pituitary gland – testes Critical stages in development Non-normal development

29 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)

30 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

31 Hypothalamus Pituitary Gonad axis
Anatomy Hypothalamus Pituitary Gonad axis

32 Gonads Testes in men Ovaries in women

33 Primary glands

34 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

35 Pituitary Gland

36 Pituitary Cyclical release of gonadotropins in females
Menstrual cycle Sexual activity in animals Steady release of gonadotropins in males

37 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

38 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?

39 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

40 Hypothalamus

41 Hypothalamus

42 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

43 Hypothalamus Might the hypothalamus be sexually di-morphic?

44 Hypothalamus 1970s: gonadotropin releasing hormone identified in hypothalamus Causes pituitary to release gonadotropins Evidence for sexual dimorphism

45 Hypothalamus – pituitary connections Neurohormonal nerve cells

46 Hypothalamus – Pituitary 2. capillary portal system

47 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.

48 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

49 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

50 Feedback circuit: Hypothalamus Pituitary Gonads

51 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)

52 Circulating Hormones Sex interest & aggression in men little influenced by testosterone levels (no testosterone reduces both; high doses of androgens may increase both)

53 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)

54 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?

55 Pre-natal hormone exposure
Androgens  “male” hypothalamus? No androgens  “female” hypothalamus?

56 Other Dimorphic Structures?
corpus callosum? Thalamus limbic system (emotion)

57 Limbic System

58 Limbic System

59 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

60 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”?)

61 Pre-natal androgen exposure
Influences average differences between males & females Influences differences among males & among females

62 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.

63 Androgen Exposure – but:
It may be estradiol that “masculinizes” Synthesized from androgens (by addition of benzene ring)

64 Pre-Natal Stages of Gender Development

65 “Adam Principle” “Nature’s impulse is to create a female”
“Default” development – no androgens  female body and brain (estrogens required at puberty)

66 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

67 Gonadal differentiation
Week 7 Y chromosome triggers TDF – testes determining factor Gonads organize as testes, begin producing androgens ONLY direct genetic influence

68 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

69 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?

70 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

71 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”

72 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.)

73 Gender Role Behavior & Sexual Orientation

74 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

75 Animal Experiments Primates: Similar effects on sexual behavior
Androgens  more “rough & tumble play”  less maternal care-taking

76 Hypothalamus & sexual orientation

77 Sexual Orientation & Roles
Gay men: “masculine” & “feminine” Lesbians: “masculine” & “feminine” Bisexuals: “masculine” & “feminine”

78 (So-called) “Normal” development
Concordance of: Genetic sex Gender identity Gender role behaviors Preponderant sexual orientation

79 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”

80 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

81 5 -Reductase Syndrome Dominican Republic: New Guinea:
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?

82 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

83 “Take Home” Points Hypothalamus – pituitary – gonadal axis
Adam Principle Gender dimorphism of hypothalamus Gender role behaviors influenced mainly by pre-natal hormones, not circulating hormones Influence on: rough & tumble play; nesting & care-taking; visual & spatial abilities; sexual orientation

84 “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

85 “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

86 “Take Home” Points -- 4 Gender Identity: don’t know cause
likely prenatal hormone influence rearing likely strong influence many cases have no clear explanation

87 “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)

88 “Take Home” Points -- 6 Sexual Orientation: likely prenatal hormone influence on homosexual vs. heterosexual orientation Also environmental influence (Sambia) transvestism & transexualism remain mysteries

89 Some Questions Role of culture: Affirm biology? Amplify biology?
Modify biology?