Nature or Nurture

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Nature or Nurture

• Genetics
• Evolutionary psychology
• Heritability Nature-nurture debates
• Sex and Gender

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Genetics

• 23 pairs of chromosomes (46 chromosomes total)
• Each chromosome is made up of helical DNA strands
• There are approximately 1000 segments called
  genes - in each chromosomal DNA
• Each gene has a partner on the paired chromosome
• Genes can be dominant or recessive
• Genes have two essential jobs
• Make copies of themselves that are transmitted
  over generations
• Direct the assembly of organisms

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More genetics

• Genes are composed of 4 different nucleotides
• There are 3 billion nucleotides
• 99.9 of the nucleotide sequences are the same in
  all human beings
• That means that there are 3 million sequences of
  nucleotides that are responsible for the
  differences amongst us
• Mice and men share 99 of the nucleotide
  sequences
• 30 million sequence differences

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Evolutionary Psychology

• Natural selection
• Individuals, whose inherited characteristics are
  adapted to their environment, survive and
  reproduce while others die.
• As a result, aspects of our behavioral and mental
  lives must have helped individuals survive and
  reproduce in the past
• Or are by-products of other aspects that have
  helped individuals survive and reproduce
• But why do we help others? Why does altruism
  exist?

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Evolutionary Psychology and Altruism

• Inclusive fitness
• Ones genes are preserved through your own
  children
• Ones genes are also preserved through the
  offspring of genetic relatives
• Kinship selection
• Helping behavior (altruism) came about because it
  increases the survival of genetic relatives
• Organisms are more apt to survive if their
  parents (or relatives) help them survive. Since
  they are more likely to have the genes that their
  parents (or relatives) have, this helping kin
  characteristic will be retained and they too
  will help their own offspring survive.

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Certainty of genetic relatedness
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Rankings of grandparent investment
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Heritability

• Genotype the specific sequence of nucleotides
  that an organism inherits
• Phenotype an organisms observable properties
• The result of what happens when genes interact
  with each other and the environment
• Heritability the degree to which individual
  differences in phenotype are determined by
  individual differences in genotype
• Heritability a statistical estimate, for a given
  trait (like intelligence), of the percentage of
  variation within a group that is due to genetic
  factors

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More on heritability The case of height
Before holding genetics constant
After holding genetics constant
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More on heritability The case of intelligence
Before holding genetics constant
After holding genetics constant
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The heritability of some human traits
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More genetics Degree of relatedness

• Each parent contributes a random selection of
  half of their genes to an offspring
• The probability of an offspring sharing any
  particular gene with a parent is .5
• Thus, the degree of relatedness between parent
  and child is .5

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Determining heritability

• Twin studies compare monozygotic (MZ or
  identical) twins raised in the same environment
  to dyzygotic (DZ or fraternal) same sex twins
  raised in the same environment.
• Holding environment constant, but varying the
  genetics
• If identical twins are more alike on the trait
  than are fraternal twins, then genetics plays an
  important role if not, then environment
• Adoption studies compare MZ twins raised in the
  same environment to MZ twins raised in separate
  environments.
• Holding genetics constant, but varying the
  environment
• If identical twins that are raised together are
  more similar than identical twins that are raised
  apart, then the environment plays an important
  role if not, then genetics

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Environmental Influences

• Even among MZ (identical) twins raised together,
  heritability of personality characteristics is
  less than 50.
• Meaning that environment must account for the
  rest of the variability.
• But if identical twins are raised together, how
  is their environment different?
• Shared vs. nonshared environments
• Shared same parents, same home, same school,
  etc.
• Nonshared occupy different niches within the
  family, may have different friends, have
  different experiences
• Some claim that it is the nonhome, nonshared
  environment that is critical in shaping the adult
  personality
• Also, genetics and environment interact

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Sex/gender differences

• Sex A biological classification based on anatomy
  and genetics
• Gender The psychological meaning of being male
  or female

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Organizational effects of hormones

• All fetuses are genetically male (XY) or female
  (XX)
• The external genitalia, reproductive systems
  (i.e., internal genitalia), and neural circuitry
  of all human fetuses begin as female
• External genitalia
• Males Urethra, penis, scrotum
• Females Urethra, clitoris, labia, vagina
• Internal genitalia
• Males Seminal vesicle, prostate, testes
• Female Ovary, fallopian tube, uterus
• At 2-3 months, a gonad (primitive sex gland)
  develops into testes (male) or ovaries (female)
• The release of androgens (e.g., testosterone) by
  testes causes the development of male external
  genitalia, male internal genitalia, and neural
  circuitry

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Demonstrations of the organizational effects of
hormones

• Monkeys pregnant with genetically female
  offspring were injected with androgen
• Offspring had penises and were more aggressive
• Rats pregnant with genetically male offspring
  experienced high emotional stress during
  pregnancy
• Offspring produced less androgen, showed unusual
  hypothalamic development, and showed less
  male-typical behavior
• Hormones are a critical determinant of sexual
  identity

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Activational effects of hormones Part One

• Beginning at puberty, hormones activate circuits
  laid down in utero and secondary sex
  characteristics emerge
• Males Testosterone causes facial, underarm, and
  pubic hair growth, lowers voice, stimulates
  muscular development, and causes genital growth
• Males first ejaculation live sperm
• Females Estrogen causes breast development,
  changes in deposition of body fat, maturation of
  external genitalia small amount of androgen
  causes pubic and underarm hair growth
• Females menarche (onset of menstruation) live
  eggs

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Activational effects of hormones Part Two

• Hormones may also have a temporary effect on
  adult sexual desire, arousal, and activity.
• Less in primates than in other mammals.
• More of an effect on males than females, but not
  as strong a relationship in males as once
  believed.
• Does female sexual desire, arousal, and activity
  vary across the menstrual cycle?
• Yes (Carter, 1991)
• No (Atkinson Hilgard, 2003)
• Also, female sexual desire does not decrease
  after menopause in humans.

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Other influences on adult sexual desire, arousal,
and activity

• Emotional factors
• The most common cause of low desire in couples
  seeking sex therapy is marital conflict (Goleman,
  1988).
• Cultural influences
• College educated adults in the US in the 1940s
• 27 of women and 49 of men had engaged in
  premarital sex by age 21
• College educated adults in the US in the 1970s
• 40-80 had engaged in premarital sex
• Laumann et al. (1994)
• 50 of men and women have sexual intercourse by
  age 16-17

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Gender identity, hormones, and environment Part
One

• Women pregnant with genetically female offspring
  took an antimiscarriage drug that promoted a
  chemical environment in the brain that was
  similar to that for a male fetus
• The offsprings sexual identity and upbringing
  was that for a girl
• Outcome slightly higher frequency of
  homosexuality and slightly lower ratings of
  maternal interest
• Environment seems more important for gender
  identity than hormones

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Gender identity, hormones, and environment Part
Two

• Androgen insensitivity
• The body tissues of genetically male fetuses that
  would normally develop into the external male
  genitalia are insensitive to androgen and, as a
  result, develop into female genitalia
• Anatomically, they are girls and they are raised
  as girls
• Genetically and hormonally, they are boys
• At puberty, the surge of testosterone turns the
  clitoris-like sex organ into a penis
• Outcome These individuals have little trouble
  adjusting to a male gender identity
• Hormones are more important for gender identity
  than environment
• Intersex

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How are men and women (psychologically)
different? Part One

• Physical aggressiveness
• Males females
• Verbal aggressiveness
• Females males
• Cognitive abilities (junior high )
• Males females at math and spatial tasks
• Females males at verbal tasks
• Social sensitivity
• Females males at using nonverbal cues (e.g.,
  facial expression and tone of voice) to determine
  how others are feeling

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Why are men and women (psychologically)
different? Nature!

• The presence of testosterone in males
• Linked to higher levels of physical
  aggressiveness in males
• Slows development of left hemisphere and enhances
  development of right hemisphere, accounting for
  cognitive (verbal spatial) differences (Benbow,
  1988 Geschwind Behan, 1982 Kimura, 1999)

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Why are men and women (psychologically)
different? Nurture!

• Gender Roles
• Sex-typed behaviors promoted by social learning
  (i.e., socialization).
• For example, girls, but not boys, are encouraged
  to play with dolls in order to learn nurturing
  behavior.
• Gender Schemas
• Beliefs about men and women that influence the
  way we perceive ourselves and others.
• Gender Stereotypes
• Simplified and exaggerated gender schemas that
  have a kernel of truth.
• Differences in gender identity could also explain
  all the (psychological) differences between women
  and men.

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A Biosocial theory of sex differences

• Perceived sex differences are magnified by
  unequal social roles occupied by men and women
  (Wood Eagly, 2002)

Biological, social, economic, and political
factors
Social roles (division of labor)
Role-consistent skills and behaviors
Gender-stereotyped social perceptions
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How are men and women (psychologically)
different? Part Two

• Sexual attitudes and behaviors
• Men females in
• Sexual promiscuity (frequency of sexual behavior
  and number of partners)
• To have sex with anyone I choose
• Sex w/o emotional commitment
• Permissive attitudes toward casual sex
• Sexual interpretation of nonverbal cues
• Fantasies about having sex with multiple partners
  simultaneously

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Gender differences in sexual motivation

• Buss (1994) argued for an evolutionary
  perspective How best are we able to pass on our
  genes?
• Women seek older and more financially secure men
  (or men who have promise of future success)
  because women are biologically limited in the
  number of children they can bear.
• Men seek fertile (young and healthy) women
  because they can father an unlimited number of
  children. Men also seek sexually faithful women
  because of paternity uncertainty.
• Personal ads reveal that men tend to seek beauty
  and offer wealth, whereas women tend to offer
  beauty and seek wealth

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Sex Differences in Marriage Age

• Men tend to marry younger women
• This age difference increases with mans age
• Women tend to marry men who are slightly older
• This changes little with age

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Sex differences in Jealousy

• Men are more concerned about sexual infidelity
  than women
• Women are more concerned about emotional
  commitment

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Other famous figures and facts in the psychology
of sex

• Alfred Kinsey surveys (1948, 1953)
• 90 of men and 50 of women had premarital sex
• Virtually all men and women masturbated
• 50 of men and 26 of women had extramarital
  affairs
• 40 of college-aged couples engaged in oral sex
• Laumann survey (1994)
• Men are 2 3 times more likely to reach orgasm
  during sex
• Women, but not men, are capable of multiple
  orgasms within a short period of time
• Masters and Johnsons (1966) four stages of the
  sexual response cycle (see next slide)

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The Sexual-Response Cycle
Masters and Johnson (1966)
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Sexual orientation

• The degree to which an individual is attracted to
  persons of the opposite sex (heterosexuality),
  the same sex (homosexuality), or both
  (bisexuality)
• 2-4 of men and 1-2 of women consider themselves
  homosexual
• The best predictor of homosexuality is a
  preference for opposite-sex activities and a
  dislike for same-sex activities as a child
• sissy behavior in boys and tomboy behavior in
  girls

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NOT predictive of homosexual orientation

• Identification with an opposite sex parent.
• Type of first sexual encounter.
• Seduction by a person of the same sex or
  admiration of a gay person.
• Feelings of attraction toward same sex typically
  occurs 3 years before homosexual activity

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Sexual Orientation Genetics and environment

• Identical twins have the highest concordance
  rates
• This suggests a genetic contribution to sexual
  orientation
• Two findings suggest some environmental
  contribution
• The rate for adoptive siblings is greater than
  zero
• The rate for identical twins is less than 100

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Other biological and psychobiological findings
and theories of homosexuality

• LeVay (1991) larger hypothalamic nucleus in
  heterosexual men than in gay men
• But no causal direction
• Did a difference in experience cause the
  difference in hypothalamus size or did the
  difference in hypothalamus size cause the
  difference in experience?
• Breedlove rat study indicating spinal nucleus
  change after environmental change
• Bems developmental theory of homosexuality
• See next slide

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Bems exotic becomes erotic theory of
homosexuality

• Genes produce differences in temperament
• Differences in temperament means that males might
  be attracted to female play
• Nonconforming males view conforming males as
  different, unfamiliar, arousing, and exotic
• At puberty, any individual is more attracted to
  the more exotic of the two sexes
• As a result, a nonconforming male will be
  attracted to males