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Module 3:
Nature and Nurture
in Psychology
Imagine for a moment that your
adoring parents, who believe you are
perfect, decide to clone you, creating
a perfect genetic replica of you.
Would the new baby, your identical
twin, grow up to be exactly like you?
What if the baby were exposed to a
different prenatal environment – one
polluted (or not) by drugs or viruses?
What if your parents had to give the
baby up for adoption or decided to
move to a different part of the world?
Behavior Genetics

School of thought that focuses on
how much our genes AND our
environment influence our
individual differences

Importance of both genetic and
environmental factors on thoughts
and behavior
Genes
 The
biochemical units of
heredity that make up
chromosomes
 Many genes together make
up chromosomes
This is a chromosome,
made up of many genes.
Environment
 Every
non-genetic influence, from
prenatal nutrition to the people and
things around us
 Any influence, other than genetic,
on an individual’s behavior
 Include:
◦ Diet (healthy vs. unhealthy)
◦ Family/home (smokers vs. nonsmokers)
◦ Cultural , religious, etc. group
◦ Home location (rural, urban)
Nature and Nurture Debate
 Nature
= the genetic code
passed from parent to child.
 Nurture = all environmental
influences from prenatal
development on.
Genetics in Brief
Chromosomes

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Found in every cell in our
body
Made up of DNA (which
contain our genes)
46 pairs of chromosomes in
each cell
23 received from each
parent
(22 pairs of autosomes and
one pair of sex
chromosomes)
Female sex chromosome =
XX
Male sex chromosome = XY
Cells – nucleus – chromosomes – DNA - genes
Chromosomes
Deoxyribonucleic Acid (DNA)
A complex molecule
containing the genetic
information
 The
“stairs” on the DNA
“ladder” are the genes
 Coded (to distinguish)
with the letters A, T, C or
G
 These individual
lettered genes are
called “nucleotides”

Interesting!!!!!!!!!!!!
A
fruit fly has about 15,000 genes
A human has only about 25,000
99.9% of your 4-letter DNA sequence is
the same as every other human; genetically,
you are nearly identical to everyone else in
the world
We are each different or unique,
genetically, by approximately 0.01%
Cellular
Makeup
Cellular Makeup
Cellular Makeup
Gene Mutation
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Errors in gene replication
that lead to a change in
an individual’s genetic
code
The source of genetic
diversity (what separates
us from the 99.9%)
Can be spontaneous or
induced
Can lead to desirable or
undesirable changes
70% of genetic mutations
are usually harmful to an
individual, the remaining
30% are neutral or mildly
beneficial
For example, a butterfly may
produce offspring with new
mutations. The majority of
these mutations will have no
effect; but one might change
the color of one of the
butterfly's offspring, making it
harder (or easier) for
predators to see. If this color
change is advantageous, the
chance of this butterfly
surviving and producing its
own offspring are a little
better, and over time the
number of butterflies with this
mutation may form a larger
percentage of the population
Predisposition
 The
possibility of something
happening based on our genes
 The environment may or may not
trigger the predisposition
 Example – disease (i.e. cancer)
Nature and
Individual
Differences
“But I….”
Despite genetics, we, as individuals often
end up very much our own person.
 What accounts for each of us being
different from all others?
 Behavior geneticists study such questions
using twin studies and adoption studies

Identical Twins
Nature’s human clones
 Develop from a single
fertilized egg that splits
in two, creating two
genetically identical
organisms
 Called monozygotic
twins

Fraternal Twins
 Twins
who developed from
separate eggs
 Genetically no more similar
than other siblings, but they
share a fetal environment
 Called dizygotic twins
Twin Studies
 Used
to determine the
heritability of a given trait
 Data is collected from both
identical and fraternal twins on
the trait
 Compare the data between
the two groups
 Important not to conclude that
a specific behavior is inherited
Evidence from Twin Studies
Intelligence
 Personality traits
 Divorce rates
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SEE HANDOUT
Adoption Studies
 Biological
parents supply the
nature and adoptive parents
provide the nurture
 Study
after study reveals that
adopted children share more
personality trait similarities
with their biological parents
than with their adoptive
parents
Environmental Factors
Early Brain Development
 Peer Influences
 Cultural Influences (norms, individualism,
collectivism)

Early Brain Development
Brain development also impacts who we
become; our thoughts and behaviors
 “Experience nurtures nature”
 The brain processes we use in early learning do
pave the way for later learning of more complex
information
 If you are raised in an impoverished environment
you will not develop to the same capacity as
someone who was; simple.
 Early experience is critical
 The brain’s pathways maintained through
practice or experience will remain strong and,
and neglected pathways will fade with disuse

Peer Influences
 Peer
influence in adolescence is
very powerful.
 Many studies suggest a peer
group is correlated with school
performance, smoking, and other
behaviors.
Culture
 The
shared attitudes, beliefs,
norms and behaviors of a group
communicated from one
generation to the next