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Psychology in Modules
by Saul Kassin
Section 8:
Nature and Nurture
Nature and Nurture
Genes
Evolution
The Nature-Nurture Debates
The Nature and Nurture Of...
Genes
What Genes Are and How They Work
Genetics
– The branch of biology that deals with the mechanisms
of heredity.
Chromosomes
– Structures that contain DNA molecules in the form of
genes.
Deoxyribonucleic Acid (DNA)
– The structure of a chromosome that carries genetic
information.
Genes
– The biochemical units of heredity that govern the
development of an individual life.
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Genes
What Genes Are and How They Work
Genetic Building Blocks
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Genes
The Human Genome Project
Human Genome
– The genetic blueprint for making a complete
human being
– The sequence of DNA is very similar in people
all over the world
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Genes
How Genes Affect Behavior
Genotype
–The underlying DNA sequence that an
individual inherits
Phenotype
–An organism’s observable properties,
physical and behavioral
Genes contribute more directly to
physical traits than to psychological
characteristics.
Evolution
Natural Selection
– The evolutionary process by which some genes in
a population spread more than others do, causing
species to change over time.
Principles of Natural Selection:
– Within a species, no two are alike.
– Individuals differ in their suitability to their
environment.
– Those better suited are more likely to survive and
reproduce.
– Reproduction perpetuates the genes of better suited
individuals.
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Evolution
Natural Selection
Adaptations
– Advantageous physical and psychological
traits that are inherited
Mutations
– Random gene copying errors that can spark
evolution by natural selection
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Evolution
Natural Selection
Natural Selection in the Galapagos
This is an example of
Finches
evolution by natural selection.
Due to the drought, an
environmental change, a
marked increase in the size of
finches occurred.
Larger birds survived and
reproduced because their
thicker beaks allowed them to
open the seeds available to
them.
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Evolution
Evolutionary Psychology
– A subfield that uses the principles of evolution to
understand human social behavior
One example is explaining why people help others.
– Inclusive Fitness
• The notion that an organism’s genes are preserved not only
through its own offspring but also through the offspring of
genetic relatives.
– Kinship Selection Theory
• The tendency for organisms to help others according to their
genetic relatedness.
– Reciprocal Altruism
• The tendency for organisms to help members of other species,
who may later reciprocate.
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The Nature-Nurture Debates
The Pursuit of Heritability
Nature-Nurture Debate
– The debate over the extent to which human
behavior is determined by genetics and the
environment.
Heritability
– A statistical estimate of the percentage of the
variability of a trait within a group that is
attributable to genetic factors.
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The Nature-Nurture Debates
The Pursuit of Heritability
Family Studies
– Studies that estimate genetic influences through
similarities of family members who vary in their
degree genetic relatedness
Twin-Study Method
– A method of testing nature and nurture by
comparing pairs of identical and fraternal twins of
the same sex
Adoption Studies
– A method of testing nature and nurture by
comparing twins and other siblings reared together
with those separated by adoption
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The Nature-Nurture Debates
The Pursuit of Heritability
Measuring the Effects of Nature and
Nurture
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The Nature-Nurture Debates
Genetic Influences
Based on the Minnesota personality studies:
– When raised together, monozygotic twins are
more similar than dizygotic twins.
– Twins raised apart are almost as similar to each
other as those living in the same home.
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The Nature-Nurture Debates
Genetic Influences
Other studies of twins and adoptees show:
– Genetic factors account for some differences in
intelligence, verbal and spatial abilities,
criminality, vocational interests, and
aggressiveness.
– There is a genetic component to psychological
disorders, such as alcoholism, depression, and
schizophrenia.
– And, there is evidence for a genetic link to
people’s attitudes toward issues and activities.
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The Nature-Nurture Debates
Genetic Influences
Heritability of Various Human
The role of genetic
Attributes
factors is shown by the
extent to which
identical twins are more
similar to each other
than are fraternal twin
pairs.
A correlation closer to
one indicates greater
similarity.
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The Nature-Nurture Debates
Genetic Influences
This study involved Heritability
672 twins who rated
Attitudes
their attitudes on
various issues and
activities.
The results show some
influence of genetic
factors.
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of
The Nature-Nurture Debates
Environmental Influences
The studies of twins and adoptees also
support the importance of environmental
influences.
– Genetic differences typically account for less than
50 percent of the variation in personality.
– Environmental factors account for the rest of the
variation.
– Nonshared environments play a vital role in a
person’s development and may be equally, or
more, significant compared to shared
environments.
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The Nature-Nurture Debates
Environmental Influences
A study of 5,542 threeyear-olds found that
– Children with older
brothers had higher
masculinity scores
– Children with older
sisters had higher
femininity scores
These results support the
nurture hypothesis.
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The Nature-Nurture Debates
The Interplay of Nature and Nurture
Genetic and environmental influences are
not independent.
– Identical twins receive more similar treatment
from their parents compared to fraternal twins.
People’s genetic makeup influences how
they are treated by others, the environments
in which they live, and the way they
perceive and recall the details of that
environment.
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The Nature and Nurture Of...
Gender: A Great Divide?
Gender differences have been found in the
following biological areas.
– Age when puberty is reached, height, weight,
fat content, and amount each sweats
– Also, women are expected to live longer than
men are.
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Gender: A Great Divide?
How Are Men and Women Different?
In the area of sexuality, men and women report
different attitudes and behaviors, with men, in
general, expressing more interest in sex.
In the area of physical aggression, men generally
are more physically aggressive compared to
women.
In the area of cognitive abilities, males tend to do
better on tests of math and spatial abilities and
females typically score higher on tests of verbal
skills.
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Gender: A Great Divide?
Why Do These Differences Between
Men and Women Exist?
Biological Perspectives
– These perspectives focus on the different
levels of sex hormones, estrogen and
testosterone, which have their greatest
impacts during prenatal development and
puberty.
Gender: A Great Divide?
Why Do These Differences Between
Men and Women Exist?
Environmental Perspectives
– Males and females have different life experiences
because of how others treat them, that is, how they
are socialized.
– Gender Roles
• Sex-typed behaviors promoted by social learning.
– Gender Schemas
• Beliefs about men and women that influence the
way people perceive themselves and others.
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Gender: A Great Divide?
Why Do These Differences Between
Men and Women Exist?
A Biosocial Theory
– Sex differences develop from an interaction
between nature (biology) and nurture
(environment).
– For example, although biological
predispositions lead to a division of labor, today
culture has a strong effect on the work roles of
men and women.
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Gender: A Great Divide?
Putting Sex Differences in
Perspective
Men and women are similar in many,
many ways.
– Differences are considered more
newsworthy.
– Therefore, the similarities among males
and females often are ignored.
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The Nature and Nurture Of...
Sexual Orientation
Origins of Homosexuality
– Both biological and environmental theories are
offered to explain the origins of sexual
orientation.
– Twin studies support the theory that sexual
orientation has biological roots.
• A survey of gay men and their twins and adopted
brothers found that 52 percent of the identical twins
were gay, while only 22 percent of fraternal twins
and 11 percent of adoptive brothers were gay.
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The Nature and Nurture Of...
Sexual Orientation
Other theorists
viewDevelopmental
sexual
Bem’s
orientation as developing
from both nature and
nurture.
Bem’s developmental theory
of homosexuality states that
genes determine childhood
behaviors that later affect
adolescents’ attraction to
either the same sex or the
other sex.
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Theory