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CHAPTER 7. The Biology of Sex and Gender Sexual Anomalies Sexual Orientation. The Biological Determination of Sex. Sex term for the biological characteristics that divide humans and other animals into the categories of male and female. Typically male or female

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chapter 7

CHAPTER 7

The Biology of Sex and Gender

Sexual Anomalies

Sexual Orientation

the biological determination of sex
The Biological Determination of Sex
  • Sex
    • term for the biological characteristics that divide humans and other animals into the categories of male and female.
    • Typically male or female
  • Gender: behavioral characteristics associated with being male or female.
  • Gender role: set of behaviors society considers appropriate for people of a given biological sex.
  • Gender identity: aperson’s subjective feeling of being male or female.
  • Not always clear cut!
sexual anomalies
Sexual Anomalies
  • Pseudohermaphrodites or intersexuals
    • ambiguous internal and external organs
    • gonads are consistent with their chromosomes
  • Occurs when internal and external genitalia do not match.
  • Several kinds of pseudohermaphrodite syndromes
    • Male to female: Deficiency in testosterone converting enzyme
    • Male to female: 5a-reductase syndrome
    • Male to female: Androgen insensitivity syndrome
    • Female to Male: congenital adrenal hyperplasia (CAH)
male sexual anomalies
Male Sexual Anomalies
  • Deficiency in testosterone converting enzyme
    • 17a-hydroxysteroid: converts testosterone into dihydrotestosterone
    • Normally: Dihydrotestosterone masculinizes external genitalia before birth
    • This does NOT occur for these individuals: stay feminized.
      • Internal development is male: testes
      • External development is female: vagina, labia
    • Get normal surge of testosterone at puberty:
      • which elicits secondary male sex characteristics- beard growth, deepening voice
      • But NOT female secondary sex characteristics (no breasts)
male sexual anomalies1
Male Sexual Anomalies
  • 5a-reductase syndrome
    • Genetic defect; common with severe inbreeding
    • Large population of 5a-reductase individuals in Dominican Republic
    • Again, no dihydrotestosterone to masculinize external genitalia before birth
    • Stay feminized.
      • Internal development is male: testes
      • External development is female: vagina, labia
    • Have external female genitalia, but testes
    • Are reared as girls from birth
    • At puberty, switch gender to male
    • Interesting because of societal/cultural effects
androgenous sexual anomalies
AndrogenousSexual Anomalies
  • Androgen insensitivity syndrome,
    • Another form of male pseudohermaphroditism
    • caused by a genetic absence of androgen receptors which results in insensitivity to androgen.
  • Ovary development suppressed by Müllerian ducts: Develop testes
    • This inhibits development of gonads into ovaries
    • BUT: Individual is resistant or insensitive to androgens
    • Thus testes develop, but do not descend
    • external genitals develop as more or less feminine.
  • In the absence of testosterone’s influence:
    • end to have well-developed breasts
    • flawless complexion
    • Vagina ends in blind pouch- no cervix or uterus
    • Generally reared as woman
    • May need estrogen therapy
    • Often identified at puberty or when can’t get pregnant
slide7

Female Sexual Anomalies

  • congenital adrenal hyperplasia (CAH)
    • results from an enzyme defect
    • Individual’s adrenal glands produce large amounts of androgen during fetal development and after birth until the problem is treated.
  • Result: masculinization of external but not internal genitalia
      • Internally female
      • Externally male
  • Parents often choose reconstructive surgery to make more female
    • reduce the size of the clitoris
    • eliminate labial fusion
    • Gives genitals a more feminine appearance.
  • If masculinization is more pronounced, the parents may decide to rear the child as a boy.
    • Surgeons finish closing the labia
    • insert artificial testes in the scrotum to enhance the masculine appearance.
slide8

Brain changes with Sexual Anomalies

  • Reversing the sex hormone balance during prenatal development changes the brain and later behavior in nonhuman animals.
  • Women born with CAH: described as tomboyish in childhood.
  • Androgen-insensitive males:
    • typically feminine in behavior
    • have a strong childbearing urge
    • decidedly female in their sexual orientation.
slide9

Brain changes with Sexual Anomalies

  • Androgen insensitive males are like females:
    • verbal ability is higher than their spatial performance
    • spatial performance is lower than that of other males.
  • CAH women more like men
    • show higher spatial ability than other women,
    • even draw pictures more typical of boys,
      • using darker colors
      • including mechanical objects
      • excluding people.
slide10

Are you sex-assigned

at birth?

  • The “neutral-at-birth” theorists:
    • claim individuals reared in opposition to their chromosomal sex generally accept their sex of rearing
    • this demonstrates that rearing has more effect of gender role behavior than chromosomes or hormones.
  • Sexuality at birth hypothesis: Milton Diamond:
    • reason individuals with ambiguous genitals accept their assigned gender is that sex of rearing is usually decided by whether the genital appearance is predominantly masculine or feminine,
    • This typically reflects the prenatal hormone environment.
  • According to Diamond: no case in the literature where an unambiguously male or female individual was successfully reared in opposition to the biological sex.
slide11

Are you sex-assigned

at birth?

Is this runner male or female?

Which sex should this individual run as?

slide12

Are you sex-assigned

at birth?

  • South African runner:
    • One of greatest female 800m runners in recent history
    • New on scene at 18 years old
    • Great controversy regarding this individual’s sex
    • Why would it matter?
      • If “she” was masculinized, would give her an unfair advantage running against women
slide13

Are you sex-assigned

at birth?

  • South African runner:
    • Testing suggests that this individual is genetically male
    • Is XY
    • Apparently has one of androgen insensitive syndromes
    • Thus: externally developed as female
    • REARED as female
    • What is s/he?
sexual orientation
Sexual Orientation
  • How many genders?
    • Anne Fausto-Sterling suggests at least five sexual categories
    • Male
    • Female
    • Three Intersexes: merm, ferm, and herm
  • Homosexuality” = preference for own sex/gender
    • homosexual men referred to as gay
    • homosexual women called lesbians.
  • Bisexual: those who are not exclusively homosexual or heterosexual
sexual orientation1
Sexual Orientation
    • Gender Nonconformity
      • a tendency to engage in activities usually preferred by the other sex
      • typical preference for other-sex playmates and companions while growing up.
      • Are tomboys gender nonconformists?
        • Society tolerates gender nonconformity differently for girls and boys
  • Data suggest that during development homosexuals do show a high rate of gender nonconformity
sexual orientation2
Sexual Orientation
  • Genetic studies provide the most documented and most consistent evidence for a biological basis for sexual orientation.
    • Homosexuality is 2 to 7 times higher among the siblings of homosexuals than it is in the population.
    • Identical twins are more concordant for homosexuality than fraternal twins or non-twin siblings.
  • Evidence of homosexual behavior in animals; not exclusively a “human” behavior
    • Usually occurs when low resources or overpopulation
    • Also occurs during pubescent play behavior
sexual orientation and brain differences
Sexual Orientation and brain differences?
  • INAH3
    • third interstitial nucleus of the anterior hypothalamus)
  • Research primarily conducted by Simon LeVay (1991)
  • INAH3 is half the size in gay men and heterosexual women compared to heterosexual men.
  • Criticism: only looked at (dead) gay men in 1980’s:
  • why is this time period and population so important?
sexual orientation and brain differences1
Sexual Orientation and brain differences?
  • Other anatomical differences have emerged more recently
    • Again supports physiological and potentially congential/genetic differences
    • Genetic vs. congenital may be important distinction
  • suprachiasmatic nucleus (SCN)
    • Has found to be larger in gay men than in heterosexual men
    • contained almost twice as many cells that secrete the hormone vasopressin.
  • Anterior commissure:
    • larger in gay men and heterosexual women than in heterosexual men
    • Involved in dual-processing across hemispheres
    • May explain some gender differences.
sexual orientation3
Sexual Orientation
  • Little is known about lesbians
    • Little data that have masculinized brains
    • Appear to perform similarly to heterosexual women on most cognitive tests
  • Two interesting physical characteristics
    • Index-to-ring finger ration of lesbians are indistinguishable
    • Tend to have weaker click-evoked autoacoustic emissions than heterosexual women (gay men have weaker than heterosexual men, as well)
    • Not know why!
sexual orientation4
Sexual Orientation
  • Bottom line: not really just two sexes
    • Anomalies occur
    • Hormone shifts/changes
    • Environmental changes/pressures
  • Homosexuality has
    • Always been around; appears to be predisposed at birth
    • Occurs in other species
    • May be explainable via biological theories