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Lecture 8

PSY354H5 Lecture Notes - Lecture 8: Blastocyst, Polyspermy, Twin

Course Code
Ashley Monks

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Tuesday, March 11, 2014
Lecture 7 (cont’d)
Sexual Orientation
The dimension of personality that describes our sexual attraction towards the two
Sexual Orientation – Self-labeling
Bisexual  increase in females than males
Gay/lesbian  more men identify as homosexual rather than bisexual or something
Something else  more women identify than men
Sexual Orientation – Development
Is it possible to detect sexual orientation early during development?
oBoys and girls who later become gay men and women engage less in
gender-typical behaviours
oSome of the boys expressed that they wanted to be girls
oThey followed the boys throughout development and compared them to
oThere was a significant proportion of boys that had feminine behaviour
that was thought to be homosexual
o11 of the boys did not grow up to be homosexual or bisexual  this is
contradictory information
oSome of these boys grew up to be heterosexual
Trying to Explain Sexual Orientation
Typically two types of theories
1. Psychodynamic: attempts to explain development in terms of internal
mental processes  social aspect of development
Rewards, punishment, socialization
2. Biological: attempts to explain development in terms of phenomena such
as brain circuitry, hormones, genes, evolution  scientific aspect of
Trying to Explain Sexual Orientation
1) Psychodynamic Models
oFirst proposed by Freud
Heterosexuality is the end point
During development, all of us go through this homosexual phase in
childhood that is forgotten when we reach this normal endpoint
Heterosexuality = ‘normal end to psychosexual development
oIncluded homosexual phase in early childhood that was later forgotten

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‘Normal development could be disrupted by abnormal relationships within the
oWould result in stuck in the homosexual phase
No scientific backing
Homosexuality results from early sexual experiences
oTraumatic (molestation, rape) or consensual
oNo scientific evidence to support
Subtle effects may be present in the expression of gender characteristics and roles
2) Biological Theories
oLeading theory: orientation reflects sexual differentiation of the brain
Influence of prenatal sex hormones
Figure: androgen levels during the sensitive period
Increased testosterone levels
More heterosexual based
Threshold indicates the larger percentage of heterosexual
men than lesbian women
Animal studies have provided some evidence
oRat preference can be altered through exposure to higher or lower levels of
oEvidence is present  but only in rats
Human experiments?
Increase in androgen levels in individuals who are naturally female
oMore likely to experience same-sex attraction and engage in same-sex
oNot perfect
LeVay’s work: Sexually dimorphic brain structures may provide clues  medial
preoptic area
INAH-3 (region that is sexually dimorphic) two- to three-times larger in
heterosexual men than in homosexual men
No difference in size between homosexual men and heterosexual women
Men studied by LeVay was smaller in volume
There was a drastic change
Quote from paper: “Based on the results of the present study as well as those of
LeVay (1991), sexual orientation cannot be reliably predicted on the basis of
INAH3 volume alone”

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LeVay’s work - Some issues to consider
Brains were from obtained via autopsy
Didn’t analyze homosexual women
Details of sexual history of homosexual men obtained through medical
Didn’t have matching records for ‘presumed heterosexual men
AIDS condition affected homosexual participants
Biological Theories
oPET scans of gay and straight people have also shown structural
oSubjects given compounds that may act as pheromones
oIncluded androstadienone (found in armpit sweat) derived from armpit
oSeveral biologically-based differences have been found experimentally
between homosexual and heterosexuals
oNone are 100% predictive or ‘diagnostic’
Confirms that many traits can be viewed as a continuum between
Exact process by which traits differentiate between the sexes as
well as between hetero- and homosexuals still not clear
oStill several questions remain
oPrenatal hormone level theory
Why do differences in androgen levels or sensitivity differ between
developing fetuses?
Endogenous and/or environmental influences?
Fetal gene expression?
oFetal Gene Expression
Family and twin studies strongly suggest that gene play a role
Monozygotic (i.e. Identical) twins are much more likely to share
the same sexual orientation
Unclear if gene expression alters prenatal hormonal pathway
Homophobia and Sexual
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