Chapter 11 Reproductive Behaviors

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Chapter 11Reproductive Behaviors
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Variations in Sexual Behavior

• Gender identity how we identify sexually and
  what we call ourselves
• Sex differences Biological differences between
  males and females
• Gender role refers to the activities and
  dispositions that a particular society encourages
  for one sex or the other

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Gender Identity

• Most people have a gender identity that matches
  their external appearance.
• Some people have a gender identity that is
  opposite their biological sex.

• Jazz is a transgender child. See her story at
• Link to Video
• (Extra credit opportunity)

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• Psychologists and researchers once believed that
  gender identity was learned and more a product of
  rearing and experience.
• Current evidence strongly suggests that
  biological factors, especially prenatal hormones,
  play a large role in gender identity.

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Variations in Sexual Development

• True hermaphrodite someone who has both
  testicular and ovarian tissuevery rare
• Hermaphrodites individuals whose genitals do not
  match the normal development for their genetic
  sex
• Intersex people are people are intermediate
  between being male or female (AKA
  pseudohermaphrodite)

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• Video Is It a Boy or a Girl? (1999)
• Link to Video, Part One
• Link to Video, Part Two
• Link to Video, Part Three

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Sex Hormone Endocrine glands

• A chemical that is secreted by a gland, conveyed
  by the blood, and affects other organs

• Glands that produce hormones

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Sex Hormones

• Two types of sex hormones include
• Androgens
• Estrogens
• Both sexes have both hormones

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Sex and Hormones

• Androgens are a groups of male sex hormones that
  include testosterone
• Generally referred to as male hormones because
  men have higher levels than women

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Sex and Hormones

• Estrogens include estradiol and others and are
  referred to as female hormones because women
  have higher levels.
• Progesterone is a type of hormone that prepares
  the uterus for the implantation of a fertilized
  ovum and promotes the maintenance of pregnancy.

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Sexual Differentiation

• Begins with the chromosomes
• At six weeks of development, both sexes have
  primitive gonads as well as
• Mullerian ducts (precursors to female
  reproductive organs-- oviducts, uterus, and upper
  vagina) and
• Wolffian ducts (precursors to male reproductive
  organs--vas deferens and seminal vesicles).

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Sexual Differentiation

• The male Y chromosome includes the SRY gene which
  causes the primitive gonads to develop into
  testes, the sperm-producing organ.
• The developed testes produce the hormone
  testosterone.
• Testosterone induces the development of the penis
  and scrotum.
• Females are not exposed to high testosterone
  levels and their gonads develop into ovaries, the
  egg-producing organs.

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Sex and Hormones

• Sensitive periods are early periods when hormones
  have long-lasting effects.
• Sexual differentiation depends mostly on the
  level of testosterone during a sensitive period.
• The human sensitive period for genital formation
  is about the third and fourth month of pregnancy.

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Sex and Hormones

• Sex hormones can have the following effects
• Organizing effects- occur mostly at sensitive
  stages of development.
• -Determine whether the brain and body will
  develop male or female characteristics
• Activating effects- occur at any time of life and
  temporarily activate a particular response.

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Congenital adrenal hyperplasia (CAH)

• XX females cortisol production leads to
  overstimulation of the adrenal gland.
• Overstimulation of the adrenal gland leads to
  extra testosterone production.
• The female fetus becomes partly masculinized.

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Congenital adrenal hyperplasia (CAH)

• Research indicates that CAH girls show a greater
  preference for boy-typical toys than do other
  girls.
• During adolescence and early adulthood, they also
  show partly masculinized interests.
• Sexual interest and activity also differs for CAH
  girls as well.

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Androgen insensitivity or testicular feminization

• XY male has the genital appearance of a female.
• Production of androgens remains normal but they
  lack the androgen receptor that enables it to
  activate genes in a cells nucleus.
• Condition occurs in various degrees from a
  smaller than average penis to genitals that
  develop a female appearance.

• Four siblings with testicular feminization
  syndrome (recessive sex-linked allele)

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5 alpha-reductase 2 deficiency

• XY males fail to produce an enzyme that converts
  testosterone to dihydrotestosterone.
• Most look female at birth but a penis develops
  during adolescence and puberty.
• Most then accept a male gender identity.
• Brain is exposed to testosterone during early
  development.

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Biological Bases of Sexual Orientation

• Research suggests that certain brain structures
  differ in size between heterosexual and
  homosexual men and women, due to the early role
  of sex hormones.
• Sexually dimorphic nucleus (SDN) an area in the
  anterior hypothalamus that is larger in the male
  and contributes to control of male sexual
  behavior, (e.g., being attracted to a female).
• Study of homosexual male brains found that their
  SDN was similar to those found in females.

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Biological Bases of Sexual Orientation

• Twin studies suggest genetic factors.
• Probability is highest in monozygotic twins and
  lower in dizygotic twins, and even lower in
  siblings and adopted brothers or sisters.
• Because monozygotic twins can have opposite
  sexual orientations, genes are not the only
  factor.

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Biological Bases of Sexual Orientation

• Sexual orientation may be influenced by
  testosterone levels during sensitive periods of
  brain development.
• Male animals deprived of testosterone early in
  life show sexual interest in other males as
  adults.
• Female animals exposed to testosterone during
  early development show an increased likelihood of
  mounting behavior.

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Biological Bases of Sexual Orientation

• Laboratory research has also shown that prenatal
  stress can alter sexual development.
• Male subjects subjected to either prenatal stress
  or alcohol developed male sexual behavior in
  addition to female sexual behaviors.
• Male subjects exposed to both stress and alcohol
  during prenatal development had decreased sexual
  behavior.

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Biological Bases of Sexual Orientation

• The probability of homosexual orientation is
  higher among men with older brothers.
• Results suggest that a mothers immune system may
  react against a protein in a son and attacks
  subsequent sons to alter development. Prenatal
  Influences, p337