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

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?