Download What biological theories have been proposed to explain gender

Psychology 320:
Gender Psychology
Lecture 16
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Announcement
I will hold additional office hours in preparation for the
midterm exam:
Thursday, October 21: 2:00-3:00 PM, 3:30-5:00 PM
Friday, October 22: 11:30 AM-1:30 PM, 3:30-4:30 PM
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Biological Theories of Gender Differences
1. What biological theories have been proposed to
explain gender differences? (continued)
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By the end of today’s class, you should be able to:
1. describe the process of prenatal sex differentiation.
2. review evidence that supports genetic contributions
to sex differences in psychological characteristics.
3. identify three classes of sex-related hormones.
4. review evidence that supports hormonal contributions
to sex differences in psychological characteristics.
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What biological theories have been proposed to explain
gender differences? (continued)
2. Genetic Theories
 Sex determination occurs at conception.
 The fertilized egg contains 23 pairs of
chromosomes—the pair that determines the sex of
the individual is pair number 23.
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 Those individuals who inherit two X chromosomes
develop into females; those individuals who inherit
an X chromosome and a Y chromosome develop
into males.
 Only the sperm cell is capable of contributing a Y
chromosome. Thus, the sperm cell determines the
sex of the offspring.
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 The Y chromosome carries a gene (SRY gene) that
acts as a “switch” for maleness, initiating processes
that result in the development of a male offspring.
 During the 7th week of gestation, the SRY gene
directs the production of testis-determining factor
(TDF). TDF triggers the development of testes,
rather than ovaries, from embryonic gonad tissue.
 Androgenic hormones from the testes (i.e., müllerian
inhibiting factor, testosterone) enable further development of the male internal reproductive system.
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NO ANDROGENIC
HORMONES
ANDROGENIC
HORMONES
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 Research suggests that, in addition to sex
differentiation, genes influence gender development.
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 Example 1: Twin Studies
Lippa and Hershberger (1999)
• Analyzed data collected from 839 same-sex pairs
of twins.
• Among the measures that participants completed
were: the Adjective Checklist, occupational
interests, and frequency of everyday activities.
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• Heritability statistics obtained:
Masculine instrumentality = .36
Feminine expressiveness = .38
GD = .53
• These findings replicate the results of several other
studies.
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 Example 2: Genetic Atypicalities
Klinefelter Syndrome
• Results from an extra X chromosome in males
(XXY).
• Those with Klinefelter syndrome develop testes,
a penis, and a scrotum, although these
structures may be relatively small and
associated with sterility.
• Incidence: 1/1000 – 3/1000 live births.
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• Physical symptoms include:
small firm testes
small penis
underdeveloped muscles
rounded body type (i.e.,
wide hips)
abnormal body
proportions
tall build
gynecomastia
reduced facial/body hair
language learning impairment
decreased libido
infertility
epilepsy
• Psychological symptoms include: “incomplete
masculinization.”
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3. Hormonal Theories
 Circulating hormones influence the differentiation of
the sexual reproductive system, affect the
development of the central nervous system, and
influence both psychological processes and
behaviour.
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 There are three primary classes of sex-related
hormones:
Estrogens (e.g., estradiol, estrone; in relatively high
concentrations in females).
Progestins (e.g., progesterone).
Androgens (e.g., testosterone, androstenedione; in
relatively high concentrations in males).
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 Estrogens and androgens are particularly important
in the sex differentiation of the reproductive system
of the fetus, the maturation of the reproductive
system at puberty, and the development of
secondary sex characteristics at puberty.
 Research suggests that, in addition to sex
differentiation, hormones influence gender
development.
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 Example 1: Non-Human Animal Experiments
vom Saal, Grant, McMullen, and Laves (1983)
• Contrasted the behaviour of male mice exposed to
high prenatal testosterone levels and male mice
exposed to low prenatal testosterone levels.
• Target embryos were “placed” between two male
siblings or two female siblings, resulting in
differential exposure to testosterone.
• Males exposed to higher testosterone levels
displayed more aggressive behaviour postnatally.
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Biological Explanations of Gender Differences:
1. What biological theories have been proposed to
explain gender differences? (continued)
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