Principles of operant conditioning have been used to help explain why people get attached to “lucky” hats, charms, and rituals.
Principles of operant conditioning have been used to help explain why people get attached to “lucky” hats, charms, and rituals.
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Psychology Twelfth Edition
Chapter 3 Genes, Evolution,
and Environment
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Unlocking the Secrets of Genes
• LO 3.1.A Explain how genes, chromosomes, DNA,
and genomes all relate to one another.
• LO 3.1.B Explain why the study of epigenetics
offers an important avenue for understanding the
genetic components of thought and behavior.
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The Human Genome (1 of 8)
• In general, behavioral geneticists study our
differences, such as those originating in heredity.
• Researchers attempt to tease apart the relative
contributions of:
– heredity
– environment
• They adopt a nature and nurture approach in their
investigations.
Principles of operant conditioning have been used to help explain why people get attached to “lucky” hats, charms, and rituals.
Copyright © 2017, 2014, 2011 Pearson Education, Inc. All Rights Reserved
The Human Genome (2 of 8)
• Genes, the basic units of heredity, are located on
chromosomes, which consist of strands of DNA.
• Each sperm cell and each egg cell (ovum)
contains 23 chromosomes.
• At conception, the fertilized egg and all the body
cells that eventually develop from it (except for
sperm cells and ova) contain:
– 46 chromosomes
– arranged in 23 pairs
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The Human Genome (3 of 8)
• Our genes, together with noncoding DNA, make
up the human genome.
– Many genes contribute directly to a particular trait.
– Others work indirectly by switching other genes on or
off.
– Many genes are inherited in the same form by
everyone.
– Others vary, contributing to our individuality.
Principles of operant conditioning have been used to help explain why people get attached to “lucky” hats, charms, and rituals.
Copyright © 2017, 2014, 2011 Pearson Education, Inc. All Rights Reserved
The Human Genome (4 of 8)
• Most human traits depend on more than one gene
pair.
• This makes tracking down the genetic
contributions to a trait extremely difficult.
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The Human Genome (5 of 8)
• However, advances in technology now permit
scientists to carry out:
– genome-wide association studies
examining variations in many DNA elements at once
– whole-genome sequencing
examines the entire 3 billion base pairs of DNA
• The researchers start by looking for DNA
differences called genetic markers.
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The Human Genome (6 of 8)
• Locating a gene does not automatically tell us:
– what it does
– how it does it
– how multiple genes interact and influence behavior
• Usually, locating a gene is just the first small step
in understanding exactly what it does and how it
works.
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The Human Genome (7 of 8)
Figure 3.1
Genes and Chromosomes
Science Source
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The Human Genome (8 of 8)
Figure 3.2
DNA Double Helix
Africa Studio/Fotolia
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Epigenetics (1 of 2)
• Many people think of the genome as a static
blueprint, a set of coded messages that never
changes over a person’s lifetime.
• But this is a big misconception.
• The genome changes over time because of:
– mutations that arise before or after birth
– epigenetic changes that affect the expression (activity)
of specific genes without altering the sequence of
bases in those genes
Principles of operant conditioning have been used to help explain why people get attached to “lucky” hats, charms, and rituals.
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Epigenetics (2 of 2)
• Mutations and epigenetic changes can be affected
by environmental factors.
– Example: Epigenetic changes may help explain why
one identical twin might get a disease and the other not
get it.
• Epigenetic changes affect:
– behavior
– learning and memory
– vulnerability to mental disorders
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The Genetics of Similarity
• LO 3.2.A Explain how natural selection contributes
to changes in gene frequencies in a population.
• LO 3.2.B List and describe five innate human
characteristics.
Principles of operant conditioning have been used to help explain why people get attached to “lucky” hats, charms, and rituals.
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Evolution and Natural Selection (1 of 3)
• Evolutionary psychologists study our
commonalities:
– personality
– emotion
– sexual behavior
– reasoning
• They trace these to the processes of evolution,
especially the process of natural selection.
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Evolution and Natural Selection (2 of 3)
• They draw inferences about the behavioral
tendencies that might have been selected.
• These tendencies:
– helped our forebears solve survival problems
– enhanced reproductive fitness
• They then conduct research to see if such
tendencies actually exist throughout the world.
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Evolution and Natural Selection (3 of 3)
• Many evolutionary psychologists believe that the
mind is not a general-purpose computer.
• It is viewed as a collection of specialized mental
modules to handle specific survival problems.
– a module does not have to correspond to one specific
brain area
• Critics are concerned that the notion of mental
modules might lead to misguided assumptions.
– namely, that virtually every human activity and capacity
is innate
Principles of operant conditioning have been used to help explain why people get attached to “lucky” hats, charms, and rituals.
Copyright © 2017, 2014, 2011 Pearson Education, Inc. All Rights Reserved
Innate Human Characteristics (1 of 2)
• Because of the way our species evolved, many
abilities, tendencies, and characteristics are:
– either present at birth in all human beings, or
– develop rapidly as a child matures
• Examples of traits:
– inborn reflexes
– an attraction to novelty
– a motive to explore and manipulate objects
– an impulse to play
– the capacity for certain basic cognitive skills
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Innate Human Characteristics (2 of 2)
• There are adaptive and evolutionary aspects of:
– sensory and perceptual abilities
– learning
– ethnocentrism
– cognitive biases
– memory
– emotions and emotional expressions
– stress reactions
– the tendency to gain weight when food is plentiful
– attachment to others
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Our Human Heritage: Courtship and
Mating
• LO 3.3.A Compare the sexual strategies of
females and males, according to the
sociobiological perspective.
• LO 3.3.B Discuss four challenges to the
evolutionary view of human mating strategies.
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Evolution and Sexual Strategies (1 of 3)
• Sociobiologists and evolutionary psychologists
argue that males and females have evolved
different sexual and courtship strategies.
• These have evolved in response to survival
problems faced in the distant past.
Principles of operant conditioning have been used to help explain why people get attached to “lucky” hats, charms, and rituals.
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Evolution and Sexual Strategies (2 of 3)
• In this view, it has been adaptive for:
– males to be promiscuous, to be attracted to young
partners, and to want sexual novelty
– females to be monogamous, to be choosy about
partners, and to prefer security to novelty
• Evolutionary psychologists research
commonalities in human mating and dating
practices around the world.
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Evolution and Sexual Strategies (3 of 3)
Figure 3.3
Preferred Age in a Mate
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The “Genetic Leash” (1 of 3)
• Critics argue that evolutionary explanations of
infidelity and monogamy:
– are based on simplistic stereotypes of gender
differences
– that they rely too heavily on answers to questionnaires,
which often do not reflect real-life choices
– that convenience samples used in questionnaire
studies are not necessarily representative of people in
general
– that the evolutionary emphasis on the Pleistocene Age
may not be warranted
Principles of operant conditioning have been used to help explain why people get attached to “lucky” hats, charms, and rituals.
Copyright © 2017, 2014, 2011 Pearson Education, Inc. All Rights Reserved
The “Genetic Leash” (2 of 3)
• Moreover, our ancestors probably did not have a
wide range of partners to choose from.
• Evidence suggests that what may have evolved is
mate selection based on:
– similarity
– proximity
• The central issue dividing evolutionary theorists
and their critics is the length of the “genetic leash.”
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The “Genetic Leash” (3 of 3)
Figure 3.4
Attitudes toward Chastity
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The Genetics of Difference
• LO 3.4.A Explain what heritability refers to, and
discuss three important facts about heritability that
should be kept in mind when discussing genetic
contributions to behavior.
• LO 3.4.B Outline the basic design of a heritability
study that involves twins and adoptees.
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The Meaning of Heritability (1 of 2)
• Heritability refers to the extent to which differences
in a trait or ability within a group of individuals are
accounted for by genetic differences.
• Heritability estimates do not apply to specific
individuals or to differences between groups.
• They apply only to differences within a particular
group living in a particular environment.
– Example: Heritability is higher for children in affluent
families than in impoverished ones.
Principles of operant conditioning have been used to help explain why people get attached to “lucky” hats, charms, and rituals.
Copyright © 2017, 2014, 2011 Pearson Education, Inc. All Rights Reserved
The Meaning of Heritability (2 of 2)
• Even highly heritable traits can often be modified
by the environment.
• Behavioral geneticists have found many examples
of how genes interact with the environment.
– Although height is highly heritable, malnourished
children may not grow to be as tall as they would with
sufficient food.
– Children who eat an extremely nutritious diet may grow
to be taller than anyone thought they could.
– The same principle applies to psychological traits and
skills.
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Computing Heritability (1 of 3)
• Behavioral geneticists often study differences
among individuals by using data from studies of:
– adopted children
– identical and fraternal twins
• By comparing the genetic and environmental
“overlap,” researchers can estimate the heritability
of a trait.
– Example: If identical twins are more alike than fraternal
twins, then the increased similarity must be due to
genetic influences.
Principles of operant conditioning have been used to help explain why people get attached to “lucky” hats, charms, and rituals.
Copyright © 2017, 2014, 2011 Pearson Education, Inc. All Rights Reserved
Computing Heritability (2 of 3)
Figure 3.5
Heritability and Adoption
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Computing Heritability (3 of 3)
Figure 3.6
Twins and Genetics
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Our Human Diversity: The Case of
Intelligence
• LO 3.5.A Discuss the extent to which intelligence may
be heritable.
• LO 3.5.B Explain why both between-group and within
group variability are important in arguments about
group differences in intelligence.
• LO 3.5.C List four ways that the environment nurtures
or thwarts mental ability, and give an example of each.
• LO 3.5.D Explain how both nurture and nature play an
interactive role in shaping behavior.
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Genes and Individual Differences (1 of 4)
• Heritability estimates for intelligence (as measured
by tests of one’s intelligence quotient, or IQ)
average about:
– .40 to .50 for children and adolescents
– .60 to .80 for adults
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Genes and Individual Differences (2 of 4)
• Identical twins are more similar in IQ-test
performance than fraternal twins.
• Adopted children’s scores correlate more highly
with those of their biological parents than with
those of their nonbiological relatives.
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Genes and Individual Differences (3 of 4)
• These results do not mean that genes determine
intelligence.
• The remaining variance in IQ scores must be due
largely to environmental influences.
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Genes and Individual Differences (4 of 4)
Figure 3.7
Correlations in Siblings’ IQ Scores
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The Question of Group Differences (1 of 3)
• If genes influence individual differences in
intelligence, do they also help account for
differences between groups?
• This question has enormous political and social
importance.
• It is a mistake to draw conclusions about group
differences from heritability estimates based on
differences within a group.
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The Question of Group Differences (2 of 3)
• The available evidence fails to support genetic
explanations of black–white differences in
performance on IQ tests.
• Even among groups popularly thought to be high
achievers, purely genetic explanations are
unsatisfactory.
– Ashkenazi Jews
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The Question of Group Differences (3 of 3)
Figure 3.8
The Tomato Plant Experiment
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The Environment and Intelligence (1 of 5)
• Environmental factors are associated with lower
performance on intelligence tests:
– poor prenatal care
– malnutrition
– exposure to toxins
– stressful family circumstances
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The Environment and Intelligence (2 of 5)
• Conversely, a healthy and stimulating environment
can raise IQ scores.
• Certain kinds of enrichment activities can improve
performance.
– Example: Attending a good-quality preschool increases
the reading and math skills of children from racial and
ethnic minorities.
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The Environment and Intelligence (3 of 5)
• Children’s mental abilities improve when their
parents:
– talk to them about many topics
– describe things accurately and fully
– encourage them to think things through
– read to them
– expect them to do well
• Children’s abilities also improve when their peers
value and strive for intellectual achievement.
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The Environment and Intelligence (4 of 5)
• IQ scores have been rising in many countries for
several generations, most likely because of:
– improved education
– better health
– increase in jobs requiring abstract thought
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The Environment and Intelligence (5 of 5)
Figure 3.9
Climbing IQ Scores
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Beyond Nature versus Nurture (1 of 3)
• The development of a human being (or other
animal) is the result of a constant dialogue
between:
– the genome and
– its environment
• The interaction between genes and environment
is far more complex than anyone previously
imagined.
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Beyond Nature versus Nurture (2 of 3)
• Genes influence which environments people find
most congenial.
• Environmental factors influence the genome by
their effects on mutations and epigenetic changes.
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Beyond Nature versus Nurture (3 of 3)
• Development of a person is the result of:
– a dynamic dialogue between genes and the
environment
– the addition of chance events
• Genetic and environmental influences blend and
become indistinguishable in the development of
any one person.
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