Download Chapter 3 Nature, Nurture, and Human Diversity

Myers’ PSYCHOLOGY
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The Nature and Nurture of Behavior
• Behavior Genetics: Predicting Individual
Chapter 3
Nature,
Nurture, and
Human
Diversity
•
•
•
•
•
Differences
Evolutionary Psychology: Understanding
Human Nature
Parents and Peers
Cultural Influences
Gender Development
Reflections on Nature and Nurture
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Nature and Nurture
• Basic question is origin of commonalities and
differences among individuals and groups in
psychological characteristics
– Two categories of variables
- 1. Nature: Inherited tendencies
• Genes, heredity
- 2. Nurture: Environmental variables
• Biological: intrauterine, nutrition, ...
• Psychological: child-rearing, schooling, ...
• Both important
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Behavior Genetics
• Outline
– Genes: Our Codes for Life
– Twin Studies
– Temperament Studies
– Heritability
– Gene-Environment Interaction
– The New Frontier: Molecular Genetics
• Begin with a bit of a warning
– Begin with Nature side of equation
– Precedes environmental influences
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Genetic Does Not Equal Immutable!
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Diet and Adult IQ of PKU Children
• People sometimes think wrongly that genetic
causes for some condition means that
condition (or trait in psychology) is immutable
(i.e., unchangeable)
• Not true. Many genetic conditions can be
ameliorated (i.e., improved) by environmental
factors
• Example of PKU (recessive genetic disorder):
untreated PKU people have very low IQs (less
than 50 by one source), but with dietary
treatment … (+1 +2)
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Genes: Our Codes for Life
• See Diagram (+1)
– Chromosomes: Threadlike structures made of
DNA that contain genes
– DNA (deoxyribonucleic acid): Molecule with
genetic information making chromosomes
(double helix)
– Genes: Segment of DNA capable of synthesizing
proteins
– Genome: Complete instructions to make
organism
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Comparison
of Relative
Size
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Karyotype of normal male fetus
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Karyotype of Down’s Syndrome (Trisomy
21) Male
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Genes
• Genes and Inheritance of traits
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Dominant
&
Recessive
Genes
– Offspring receive half of chromosomes from
mother and half from father
– Some traits associated with single or few genes
- Traits dominant or recessive, some sex linked (+1 +2)
– Other traits associated with multiple genes
- Produce quantitative differences on trait, often
approximated by normal curve (e.g., height,
intelligence, aggression, sociability) (+3)
– From Genes to Behavior
- “Missing link” is often what and how biochemical
processes controlled by Genes lead to psychological
traits and behaviors
Genes and Colour
Blindness
• What shapes
and numbers
do you see in
figures below?
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Polygenic
Traits
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0 .0 0 0 0
5 .0 0 0 0
1 0 .0 0 0 0
x
• Imagine trait influenced by 10 independent genes,
each of which is 0 half the time or 1 half the time
• Trait strength is determined by the number of 1s:
scores could range from 0 (all 0s) to 10 (all 1s)
• Probability of different strengths shown in graph
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Genetic mutations
• In addition to normal inheritance, mutations
influence transmission/acquisition of traits
• Conditions possibly related to mutations
include schizophrenia: e.g., children of older
fathers more susceptible (3%) than children
of younger fathers (1%)
• Some mutations adaptive: e.g., sickle cell
anemia more common in Africans and their
descendents because sickle cell mutation
“protects” somewhat against malaria
Behaviour Genetics
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• Twin Studies
– Identical and Fraternal twins (+1)
– Identical more similar in many areas (+2)
-
Alzheimer’s
Personality traits (extraversion)
Divorce
Abilities (later slide)
Schizophrenia (later slide)
– Separated Twin Studies: MZ more similar than
DZ even if reared apart on many traits studied
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Behavior Genetics
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• Identical Twins: single zygote (fertilized egg)
that splits in two, creating two genetic replicas
• Fraternal Twins: separate zygotes, genetically
no closer than brothers and sisters, but share
fetal environment
Genetic Influences
Similarity of 1.0
intelligence
0.9
scores
(correlation) 0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
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• Most
genetically
similar
people have
most similar
scores
• Recall that r
varies from
0 indicating
no relation
to +/- 1,
indicating
Identical Identical Fraternal Siblings Unrelated
reared individuals
perfect
twins
twins
twins
together reared
reared
reared
reared
relation
together
together apart
together
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Behaviour Genetics
• Adoption Studies
– Similarity of offspring to biological (genetic) and
adoptive (environmental) parents
– In many traits, children more similar to biological
parents (+1)
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Schizophrenia
Lifetime risk
of developing
schizophrenia
for relatives of
schizophrenic
40
30
20
10
0
General
Siblings
population
Children
Fraternal Children Identical
twin
twin
of two
schizophrenia
victims
Genetic Influences
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0.35
Child-parent
correlation in 0.30
verbal ability
scores 0.25
Children and their
birth parents
0.20
0.15
Adopted children
and their birth
parents
0.10
Adopted children
and their adoptive
parents
0.05
0.00
3 years
16 years
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Temperament Studies
• Person’s characteristic
• Survey of parents in mid 1990s measured “difficult
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temperament” with questions such as:
– "How easy or difficult is it for you to calm or soothe him or her when he
or she is upset?“
– "How many times per day, on average, does he or she get fussy and
irritable?“
– "How much does he or she smile and make happy sounds?“
– Final score out of 50 determined by adding up values for each question
emotional reactivity and
intensity
– Even young infants show
differences in temperament (+1)
- Some excitable and emotionally
reactive
- Others calm and easygoing
– Correlates with adult behaviour
– Also observed in animals
– Some cultural differences perhaps explained by genetic
differences
- Asian infants more calm, Aboriginal babies and restraint (above)
Behavior Genetics
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Genetic Influences
• Group differences below due to environmental factor
• Heritability
(soil fertility), not heritability (within-group variation)
– Proportion of variation among individuals
attributed to genes: 40-50% in many areas
– Depends on range of populations and
environments studied
– Within-group variation: may not explain
between-group differences (+1)
Variation within group
Variation within group
Seeds
• Interaction
– Effect of one factor (such as environment)
depends on another factor (such as heredity)
Poor soil
Fertile soil
Difference between groups
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Gene by Environment Interaction
• Cooper & Zubeck
– Bred maze-bright and
maze-dull rats
– Reared them in
various environments
- Impoverished, Normal,
Rich
– Observed number of
errors on mazelearning task
– Strong Gene x
Environment
interaction
New Frontier: Molecular
Genetics
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• Attempt to identify specific genes associated
with behaviours and disorders
– Compare genetic make-up of affected and nonaffected people
– Identify gene or genes that distinguish groups
• Important to remember that genes influence
underlying biochemical processes; they do
not transmit traits directly
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Evolutionary Psychology:
Understanding Human Nature
• Outline
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Religiousness and Evolution
– Natural Selection
– An Evolutionary Explanation of Human Sexuality
– Critiquing Evolutionary Perspective
• Introduction
– Explains universal behaviours in terms of shared
biological foundations arising from Natural
Selection
– Based on Darwinian model, which is widely
accepted by scientists but still controversial
among public (+1)
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Evolutionary Psychology
• Variation + Natural Selection
– Random combinations and
mutations produce variation in
members of species
– Genes that promote
reproductive success favoured
– Results in physical and
behavioural adaptations that
persist today
Charles Darwin
1809-1882
Biological
Preparedness: Fears
• Do organisms have
innate fear of some
objects (e.g., snakes,
spiders, …)?
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• Wild monkeys show intense fear of snakes, but not
captive raised monkeys. Suggest fear learned, but …
• Nonfearful Monkeys who see single example of
another monkey responding fearfully to snake acquire
fear (but not flowers or other non-dangerous objects)
• Suggests organisms have innate preparedness to fear
snakes, but this predisposition needs to be activated
by single exposure to appropriate model
- Fear of spiders and snakes (+1)
- Gender differences in sexual
behaviours (later)
– 40 years of breeding foxes for
tameness (bottom right)
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Genes and Human Variation
• Peoples of world remarkably similar in genetic
make-up and numerous behaviors
– E.g., emotional expressions largely universal
• Genes also contribute to ways in which groups
differ from one another
– Groups of people differ with respect to genetic similarity
depending on evolutionary migration (+1)
– Much current research on genetic bases for ethnic
differences in disease, drug treatment, and other medical
domains
– Less research on psychological implications
– Some resistance among social scientists to attribute
group differences to genetic differences
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Evolutionary Explanation of Human
Sexuality
• Gender and Human Sexuality
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Evolutionary Psychology
• Mating Preferences
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– Men everywhere preferred attractive physical features
suggesting youth and health
– Women preferred men with resources and status
– Males more likely to initiate sexual activity
– Males more accepting of casual sex
- FSU researchers: “Would you go to bed with me
tonight?” asked of strangers
- 0% of women accepted, and 75% of men
– Males more likely to masturbate, and more often
– Males 80% of customers of adult video stores
– Males think about sex more often
– Males higher risk takers (attracting mate)
– Gender differences in mating preferences around
world (+1)
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Evolutionary “Explanation”
• Biologically, sperm “cheap” relative to eggs
• Male can spread sperm around to multiple
recipients, while female must incubate and
nurse one infant at a time
• Hence, men pair widely while women pair
wisely
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Critiquing Evolutionary Perspective
• Scientific Criticisms
– Hindsight explanations can explain anything
– Fail to explain some findings: e.g., some female monkeys
mate with numerous males
– Lack of mediating mechanisms
• Societal Criticisms
– Perpetuate gender stereotypes and other negative social
consequences.
– Evolutionary psychology proposes genetic determinism and
undercuts morality in establishing society.
– Universal results (e.g., preferences) may result from
universal inequities in status of men and women around
world
– Ignores commonalities, such as preference of both males
and females for similar traits in partners
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Environmental Influences
• What explains other 5060% of variability?
• Various Environmental
influences
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Prenatal Environment
• Some identical twins (below) share more
similar intrauterine environment than other
identical and fraternal twins and non-twins
– Parents and Early
Experiences
- Prenatal environment
- Experience and brain
development
- Role of Parents
– Peer influence
– Culture
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Prenatal
Environment
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Environmental Influence
• Experience affects brain development
• Teratogens
(also +1)
– More in Ch. 4
• Cocaine and Heroin
– miscarriage or premature birth
– birth defects
• Alcohol
– Fetal Alcohol Syndrome
– Motor development problems
Impoverished
environment
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Environmental Influence
Rat brain
cell
Enriched
environment
Rat brain
cell
Parents
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• Surprisingly (to many
• A trained brain: left=before and
people) parental influence
appears to be rather weak:
see works by Judith Harris
• Plomin & Daniels (1987)
wrote:
right=after finger-tapping practice
– “Two children in the same
family [are on average] as
different from one another
as are pairs of children
selected randomly from the
population”
Environment: Peer Influence
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• Peers powerful socializing factor on children
– e.g., immigrant children strongly influenced by school-mates and friends;
often dramatic and sudden changes from parent’s generation
– e.g., peer influence on adolescent smoking (below)
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Environment: Culture
• Culture
– Behaviours, ideas, attitudes, and traditions shared
by large group of people and transmitted from one
generation to next
– Some cultures homogeneous (e.g., traditional
Japan)
– Cultures vary in many ways
-
Norms (e.g., for eating)
Personal space
Expressiveness
Pace of life
Child-rearing (e.g., collectivism vs. individualism and
promotion of independence in children)
– Cultures also evolve over time, sometimes quickly
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Culture
• Individualism-Collectivism
– A major distinction between cultures
– Individualist cultures
- Independent self, abstract principles of morality,
confrontation allowed in relationships, …
- E.g., Canada and other English-speaking nations,
Northern Europe, …
– Collectivist cultures
- Interdependent self, morality defined by social networks
(duty), harmony important in groups, …
- Mediterranean Europe, Asia, ….
– Other contrasts (+1)
• Marked differences in
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child-rearing practices
across cultures, perhaps Culture and
associated with
Child-rearing
individualism-collectivism
• Consider example of Gender Similarities and
Differences in more detail
– Biological and Environmental influences
• Biological Factors
– Sleep alone vs. with
Mother and perhaps other
family members
– Promote Independence vs.
strong Emotional
attachment to care-giver(s)
and Obedience
– Nuclear family vs.
Extended family
The Nature and Nurture of Gender
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Gender Development
– X and Y Chromosomes: Sex chromosomes for women
(XX) and men (XY)
– Testosterone
- Primary male sex hormone
- Present in both males and females, but more in males
• Influences brain development in fetus
• Development of male sex characteristics at puberty
• Related to some traits (e.g., aggression)
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• Nurture of Gender
The Nature and Nurture of Gender
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Gender and Culture (1994)
– What is acquired?
- Gender Role: expected behaviors for males and for
females
- Gender-typing: acquisition of a traditional masculine or
feminine role
- Gender Identity: one’s sense of being male or female
– Differences across cultures (+1)
– Changes in Western cultures (+2)
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The Nature and Nurture of Gender
Gender
Theories
• Two theories (above)
– Social Learning Theory: learn social behavior by
observing & imitating and by being rewarded or punished
– Gender Schema Theory: children learn what it
means to be male and female, and adjust behavior
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Reflections on Nature and Nurture
• Genes and Experience together form who we
are (+1)
• We are both creatures and creators of our
worlds
• Some troubled by naturalism of science
– Appears to leave little room for Spirituality
– Interestingly, Myers himself is deeply religious
person (he has many religious writings that can be
found on www), so science and religion can be
reconciled by some people. Even Pope John Paul
endorsed evolution as “more than a theory.”
– Also true, however, that many who accept science
do tend to leave religion behind
Evolution and Religion
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• Myers (p. 135-136)
– Some positive dialogue between representatives of
religious groups and science
- Pope John Paul, 1996: “evolution more than just a
theory”
– Myers also cites some scientists (?)
- Quotes could be interpreted as consistent with intelligent
design (nature “cunningly devised”)
- ID viewed by many scientists, even believers, as pseudoscience
– Also states
Science and Religion
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• Important and much-discussed issue
– Googling “science religion” reveals 30,000,000
hits
– Many have to do with conflict between and / or
reconciliation of two
• One of issues you may face as university
student is difference of worldview presented
in psychology and other university classes
from your traditional views acquired from
family, past teachers, society, …
- “On most of these matters, science is silent”
- But, supposed limits of science have never lasted
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