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Behavior Genetics: Predicting
Individual Differences
Introduction
• Behavior genetics
– Relative importance of heredity and
environment on behavior
Genes: Our Codes for Life
• Chromosomes
– (46 – 23 from each parent)
• DNA (deoxyribonucleic acid)
• Genes (30,000)
– Active (expressed)
vs. inactive
– Self-regulating
• Genome
– Complete instructions
– Variations at gene site define
– each person’s uniqueness
Genes: Their Location and
Composition
In the nucleus of every cell we have 46 chromosomes…
Except……
Chromosome Breakdown
Chromosomes
Genes
DNA
Nucleotides
Genetic Similarities
Mr. C is
95%
99.5%
99.5%
Human Genome Project
Genetic Revolution
• Questions to discuss:
1) If it were possible, would you want to take a
genetic tests telling you which diseases you are
likely to suffer from later in life?
2) When you are married, suppose you or your
partner are pregnant. Would you want to take a
genetic test telling you which diseases your child
is likely to suffer from later in life?
3) Do you think it should be legal for employers to
use genetic tests in deciding whom to hire?
Twin and Adoption Studies
Identical Versus Fraternal Twins
• Identical twins
• Fraternal twins
Twin and Adoption Studies
Identical Versus Fraternal Twins
Twin and Adoption Studies
Identical Versus Fraternal Twins
Monozygotic
Dizygotic
Twin and Adoption Studies
Identical Versus Fraternal Twins
Monozygotic
Dizygotic
Twin and Adoption Studies
Identical Versus Fraternal Twins
Monozygotic
Dizygotic
Twin and Adoption Studies
Identical Versus Fraternal Twins
Monozygotic
Dizygotic
Twin and Adoption Studies
Identical Versus Fraternal Twins
Monozygotic
Dizygotic
Twin and Adoption Studies
Separated Twins
• How can studying twins offer insight?
– Same genetic make-up = differences due to?
• Twin Studies
– Personalities, interests, fears, abilities
– Divorce rates
• Anecdotal evidence
– Why must we be
careful in making
judgments based on
these findings?
Twin and Adoption Studies
Biological Versus Adoptive Relatives
• Genetic relatives
– Biological parents / siblings
• How similar are you to your brother or
sister in personality?
• Environmental relatives
– Adoptive parents / siblings
• Usefulness for comparison?
– Personality of adopted children
more similar to biological parents
– Attitudes, values, manners, faith,
politics = more similar to adoptive
parents
Heritability
• “Variation among individuals attributed to genes”
• Herit
– possess something someone has given you
– Inherit traits & qualities from our parents
• Ability
– suffix meaning “capable”
– If passed on, capable of showing up
Heritability
• Groups Differences
– Heritable differences DO NOT demonstrate
the relative importance of genes in
explaining traits
• Nature and Nurture
– Nature and nurture work together
– Genes are self-regulating
Gene-Environment Interaction
• Genes and experience interact
– Stressful environments + gene activation
of NT’s associated with depression
– Evocative interactions – genes can
evoke certain types of reactions
Predominantly
Environmental
Interactional
Predominantly
Genetic
Specific language
Height
Blood type
Specific religion
Weight
Eye color
Skin color
The New Frontier: Molecular
Genetics
• Molecular genetics
– Molecular behavior genetics
• ID specific genes influencing behavior
– Genetics and diseases
• ID genetic risks for diseases
– Potential Problems?
• China – selective abortions
• Other issues?
Evolutionary Psychology:
Understanding Human Nature
Natural Selection and Adaptation
• Evolutionary psychology
– How has natural selection shaped our
universal behavior tendencies?
–Natural selection
• Mutation
• Adaptation
• Fitness
Evolutionary Psychology:
Explaining Universal Behaviors
• Evolutionary psychology is the science that seeks to explain
why humans act the way they do.
• Evolutionary psychology seeks to reconstruct problems that
our ancestors faced in their primitive environments, and the
problem-solving mechanisms they created to meet those
particular challenges.
• From these reconstructed problem-solving adaptations, the
science then attempts to establish the common roots of our
ancestral behavior, and how those common behavioral roots
are manifested today in the scattered cultures of the planet.
• The goal is to understand human behavior that is universally
aimed at the passing of one's genes into the next generation.
Look at our Behaviors…
Can you answer these questions using evolutionary psychology?
1) Why do infants fear strangers when
they become mobile?
2) Why are most parents devoted to
their children?
3) Why do we divide people into
categories?
4) Why do we have more phobias about
spiders and snakes than electricity
and nuclear weapons?
Now, the big one?
How and why do men and
women differ sexually?
Sexuality and the
Evolutionary Psychologist
• Casual sex is more
accepted by men.
• When average men
and women randomly
ask strangers for sex
tonight, 75% of men
agreed, almost no
women agreed.
WHY?
Sperm is Cheap
Eggs are not
Evolutionary Success Helps Explain
Similarities
• Behaviors that contribute to survival
are found throughout cultures
Evolutionary Success Helps Explain Similarities
Outdated Tendencies
• Genetic traits which helped our
ancestors survive may harm us today
– Love for the taste of fats & sweets
– Any Others?
Critiquing the Evolutionary
Perspective
• Backward theorizing
• Impact of social influence
Reflections on Nature and Nurture
Biopsychosocial Approach to Development
The End
Definition
Slides
Behavior genetics
= the study of the relative power and
limits of genetic and environmental
influences on behavior.
Environment
= every non-genetic influence, from
prenatal nutrition to the people and
things around us.
Chromosomes
= threadlike structures made of DNA
molecules that contain the genes.
DNA (deoxyribonucleic acid)
= a complex molecule containing the
genetic information that makes up the
chromosomes.
Genes
= the biochemical units of heredity that
make up the chromosomes; segments
of DNA capable of synthesizing a
protein.
Genome
= the complete instructions for making
an organism, consisting of all the
genetic material in that organism’s
chromosomes.
Identical Twins
= twins who develop from a single
fertilized egg that splits in two, creating
two genetically identical organisms.
Fraternal Twins
= twins who develop from separate
fertilized eggs. They are genetically no
closer than brothers and sisters, but
they share a fetal environment.
Heritability
= the proportion of variation among
individuals that we can attribute to
genes. The heritability of a trait may
vary, depending on the range of
populations and environments studied.
Interaction
= the interplay that occurs when the
effect of one factor (such as
environment) depends on another
factor (such as heredity).
Molecular Genetics
= the subfield of biology that studies the
molecular structure and function of
genes.
Evolutionary Psychology
= the study of the evolution of behavior
and the mind,using principles of
natural selection.
Natural Selection
= the principle that, among the range of
inherited trait variations, those that
lead to increased reproduction and
survival will most likely be passed on
to succeeding generations.
Mutation
= the random error in gene replication
that leads to a change.