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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 PMFriday, 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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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.

What biological theories have been proposed to explain gender differences? (continued)

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Only the sperm cell is capable of contributing a Y chromosome. Thus, the sperm cell determines the sex of the offspring.

Those individuals who inherit two X chromosomes develop into females; those individuals who inherit an X chromosome and a Y chromosome develop into males.

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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.

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.

Androgenic hormones from the testes (i.e., müllerian inhibiting factor, testosterone) enable further develop-ment of the male internal reproductive system.

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ANDROGENIC HORMONES

NO ANDROGENIC HORMONES

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Research suggests that, in addition to sex differentiation, genes influence gender development.

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• Among the measures that participants completed were: the Adjective Checklist, occupational

interests, and frequency of everyday activities.

Example 1: Twin Studies

Lippa and Hershberger (1999)

• Analyzed data collected from 839 same-sex pairs of twins.

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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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• Results from an extra X chromosome in males (XXY).

Klinefelter Syndrome

• 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.

Example 2: Genetic Atypicalities

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• Physical symptoms include:

small firm testessmall penisunderdeveloped musclesrounded body type (i.e.,

wide hips)abnormal body proportions

tall build gynecomastiareduced facial/body hairlanguage learning impairmentdecreased libidoinfertilityepilepsy

• 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

• Contrasted the behaviour of male mice exposed to high prenatal testosterone levels and male mice

exposed to low prenatal testosterone levels.

vom Saal, Grant, McMullen, and Laves (1983)

• Target embryos were “placed” between two male siblings or two female siblings, resulting in

differential exposure to testosterone.

• Males exposed to higher testosterone levelsdisplayed more aggressive behaviour postnatally.

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1. What biological theories have been proposed to explain gender differences? (continued)

Biological Explanations of Gender Differences: