Transcript Untangling Nature and Nurture

Untangling
Nature and
Nurture
Behavior Genetics: the study
of the interaction of genes
and environment on behavior
Nature vs. Nurture
“Nature” = the role
that genes have on a
trait
“Nurture” = the role
that life experience
has on a trait.
Sometimes, it is
surprising.
Genes: Our Biological
Blueprint
 Chromosomes
 threadlike structures made of DNA that
contain the genes
 DNA (deoxyribonucleic acid)
 complex molecule containing the genetic
information that makes up the
chromosomes
 has two strands-forming a “double
helix”--held together by bonds between
pairs of nucleotides
Genes: Our Biological
Blueprint
 Genes
 biochemical units of heredity that make
up the chromosomes
 a segment of DNA capable of
synthesizing a protein
 Genome
 the complete instructions for making an
organism
 consisting of all the genetic material in its
chromosomes
Genes: Their Location
and Composition
Nucleus
Cell
Chromosome
Gene
DNA
Evolutionary
Psychology
 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
 Mutations
 random errors in gene replication that
lead to a change in the sequence of
nucleotides
Evolutionary
Psychology
 Evolutionary Psychology
 the study of the evolution of
behavior and the mind, using the
principles of natural selection
 Gender
 in psychology, the characteristics,
whether biologically or socially
influenced, by which people define
male and female
Evolutionary
Psychology
 Men preferred attractive physical features
suggesting youth and health
 Women preferred resources and social
status
Behavior Genetics
 Behavior Genetics
 study of the relative power and
limits of genetic and environmental
influences on behavior
 Environment
 every nongenetic influence, from
prenatal nutrition to the people and
things around us
Behavior Genetics
Identical
twins
Fraternal
twins
 Identical Twins
 develop from a single
fertilized egg that splits
in two, creating two
genetically identical
organisms
 Fraternal Twins
Same
sex only
Same or
opposite sex
 develop from separate
eggs
 genetically no closer
than brothers and
sisters, but they share
the fetal environment
Epigenetics
• Often nature and nurture
interact
• Overkalix study
– Famine in 1944
– Grandpa exposed to famine as
preadolescent = low
cardiovascular deaths of
grandsons
– Grandpa NOT exposed to famine
as preadolescent = high
diabetes mortality in grandsons.
– Granddaughters of women who
experience famine while in the
womb died earlier.
Environmental factors
can alter the expression
of genes. These changes
are called “epigenetic
tags”.
Heritability
• The percentage of trait variation in a
group that can be attributed to
genetic differences
• Depends on the population
Heritability
Sara is very
outgoing
and
agreeable
Suzy is timid
and nonconforming
If this pair of IDENTICAL twins is my population,
what percent of the personality differences is
attributable to genetic differences between them?
The heritability is 0%.
Heritability
Joe and Hank are
not related. At
birth, both were
placed in identical
environments that
were maintained
identical until they
were 10 years old.
At 10, Joe is
outgoing and
friendly.
At 10, Hank is
withdrawn and
shy.
In this (very small) population, what is the heritability of
their personality traits? In other words, what percentage of
the difference is attributable to genes?
100%
How heritable is that trait?
Trait
Population
Creativity
Extraversion
Autism
Depression
Sleep quality
TV viewing
Religious beliefs
adolescents
adults
general
general
general
3-5 year olds
general
women
general
women
Religious conservatism
Divorce
Height
Heritability
25%
30-50%
90-95%
40-55%
35%
10-45%
0%
40%
55%
92%
http://www.peele.net/lib/genes.html The Stanton Peele Addiction Website
Behavior Genetics
 Temperament
 a person’s characteristic emotional
reactivity and intensity
 Heritability
 the proportion of variation among
individuals that we can attribute to
genes
 may vary, depending on the range
of populations and environments
studied
Behavior Genetics
 Interaction
 the dependence of the effect of one
factor (such as environment) on
another factor (such as heredity)
 Molecular Genetics
 the subfield of biology that studies
the molecular structure and
function of genes
Environmental
Influence
 Two placental arrangements in
identical twins
Environmental
Influence
 Experience affects brain
development
Impoverished
environment
Rat brain
cell
Enriched
environment
Rat brain
cell
Environmental
Influence
 A trained brain
Environmental
Influence
 Culture
 the enduring behaviors, ideas,
attitudes, and traditions shared by
a large group of people and
transmitted from one generation to
the next
 Norm
 an understood rule for accepted
and expected behavior
Environmental
Influence
 Personal Space
 the buffer zone we like to
maintain around our bodies
 Memes
 self-replicating ideas, fashions,
and innovations passed from
person to person
Examples of Influence by
Age
 Drinking Age?
 Differs by culture
 Dating Age?
 Differs by culture
 Sexuality Age?
 Adulthood Age?
 Differs by culture
 Working Age?
 Differs by culture
 leaving school
 Differs by culture Age?
 Differs by culture
 Marriage Age?
 Differs by culture
Drinking Age
• The average (mean) minimum legal drinking age around
the globe is 15.9. The majority of countries have set the
drinking age at 18. In fifty countries the minimum age is
lower than 18 and in 12 countries it is higher than 18.
• The enforcement of minimum legal drinking ages also
varies widely between countries and often within countries.
In many nations the law isn’t generally enforced unless
alcohol is abused and associated with behavioral problems.
• Internationally, the average age at which drinking alcohol
first occurs is 12 years and about 80% of young people
begin drinking alcoholic beverages regularly at age 15 or
younger according to the World Health Organization
(WHO).
Dating Age
• Ranges around the world.
• India, Japan, China- Most (some
suggest 9 of 10) arranged
• Sweden- Most start around 10-11.
• U.S. – 15-17
Sexuality
The Nature and Nurture
of Gender
 X Chromosome
 the sex chromosome found in both men
and women
 females have two; males have one
 an X chromosome from each parent
produces a female child
 Y Chromosome
 the sex chromosome found only in men
 when paired with an X chromosome
from the mother, it produces a male
child
The Nature and Nurture
of Gender
 Testosterone
 the most important of the male sex
hormones
 both males and females have it
 additional testosterone in males stimulates
 growth of male sex organs in the fetus
 development of male sex characteristics during
puberty
 Role
 a set of expectations (norms) about a social position
 defining how those in the position ought to behave
The Nature and Nurture
of Gender
 Gender Role
 a set of expected behaviors for males
and females
 Gender Identity
 one’s sense of being male or female
 Gender-typing
 the acquisition of a traditional
masculine or feminine role
The Nature and Nurture
of Gender
 Gender and Culture
The Nature and Nurture
of Gender
The Nature and Nurture
of Gender
 Social Learning Theory
 theory that we learn social behavior by
observing and imitating and by being
rewarded or punished
 Gender Schema Theory
 theory that children learn from their
cultures a concept of what it means to
be male and female and that they
adjust their behavior accordingly
The Nature and Nurture
of Gender
 Two theories of gender typing
Twin Studies
Identical Twins
v.
Same genes,
Same environment
Fraternal Twins
Different genes,
Same environment
Therefore, greater differences between the two groups indicate
greater heritability (“Nature”). The trait might appear to have a large
genetic component.
Twin Studies
Increased risk of schizophrenia if twin
develops disease
60%
% increase
50%
40%
30%
20%
10%
0%
Fraternal twins
Identical twins
Criticism:
1) Do fraternal twins
really have equally
similar environments to
identical twins?
Differences in looks or
inborn temperament
may cause people to
treat you differently.
2) Identical twins may
share a placenta but
fraternal twins do not.
Thus, we can’t
eliminate prenatal
environments as the
cause of the differences
between the two
groups.
Twin Studies
Identical Twins Reared Together
Same genes,
Same environment
v.
Identical Twins Reared Apart
Same genes,
Different environment
Greater difference between these two groups indicates greater role of
the environment (“nurture”).
Twin Studies
Similarity of IQ Test Scores in Twins
Correlation
0.9
0.8
0.7
0.6
0.5
Identical twins reared Identical twins reared
together
apart
Criticisms:
1) Adoption agencies
try to place twins
in similar families
so the variation in
environment may
be small, and
2) There is a very
limited sample.
Adoption Studies
Is child more
like adoptive
parents…
…or biological
parents?
Adoptive Parents - Nurture
Biological Parents - Nature
Adoption Studies
Similarity of Temperament Between Adopted
Children and their Parents
0.5
Correlation Coefficient
Correlation Coefficient
Similarity of Values Between Adopted
Children and their Parents
0.4
0.3
0.2
0.1
0
Biological parents
Adoptive parents
0.6
0.5
0.4
0.3
0.2
0.1
0
Biological parents
Adoptive parents
• Note: Two related siblings that grow up in the same family are
strikingly different in personality (as I’m sure many of you can
attest to).
Heritability
Your turn
Analyze the behavior genetics research
data to determine the role of nature
and nurture in various traits.