Nature vs. Nurture
The Nature Argument
(is sometimes compelling)
This guy will never be….
This guy!!!
Why does Brad Pitt look the way he does?
Behavior Genetics:
The study of the power and limitations of
genes AND environment on who we are.
Genes: Our Biological Blueprint
Genes: Their Location and Composition
In the nucleus of every cell we have 46 chromosomes……
Chromosome Breakdown
Chromosomes (books)
DNA (pages)
Genes (words)
Nucleotides (letters)
What do we get from our parents?
• We inherit one set of 23
chromosomes from each
parent.
• The two sets form pairs
that contain alternate genes
for the same traits.
• Sometimes, one gene is
dominant and “overrides”
the recessive gene.
What do we get from our parents?
• Let’s take eye color.
• In humans, brown eyes are dominant
over blue eyes. If a couple who are
both heterozygous for brown eyes
reproduce with one another, what
are the chances of the child having
blue eyes?
• What if one parent is heterozygous
and one is homozygous?
Other Dominant Traits
•
•
•
•
•
Curly hair.
Unattached earlobes.
Farsightedness.
Tongue rolling
Hand clasp
Chromosomal Abnormalities
• Gender comes from
23rd pair of
chromosomes…men
have XY…woman have
XX.
• Turner’s syndrome is
single X.
• Klinefelter’s syndrome
is extra X…XXY
• Down syndrome….extra
chromosome on 21st
pair.
Genetic Similarities
99.9%
Mr. Goode is
95%
99.9%
Identical Twins
• Best way to really study
genetics because they come
from the same zygote.
• Bouchard Study
• .69 Correlational
coefficient for IQ tests of
identical twins raised apart.
• .88 raised together.
• What are the
different types of
twins?
• Monozygotic Twins
(from one egg) and
Dizygotic Twins
(from two eggs).
Twin Studies: The results
• To summarize the countless amount of
studies: Twins (especially identical),
whether or not they are raised in the
same environment are very much alike
in many ways.
Temperament
• A person’s
characteristic
emotional
reactivity and
intensity.
• It remains
relatively stable
over time.
Heritability
• The proportion of variation among individuals that we
can attribute to genes.
• It is a mathematical formula.
• Ranges from 1 (all variance due to heredity - like
tongue curling) to 0 (none due to heredity – like
speaking English).
• As environments become more similar, heredity as a
source of differences becomes more important.
• Mark Twain explains it best using the barrel example.
Heritability and Disease
Evolutionary Psychology & Natural Selection
• 1959 Russian Fox story.
• 40 Males, 100 Femalesmated - then kept only
tamest of bunch.
• Mated the tames.
• 40 years later…
• New Breed of Fox!
Evolutionary Psychology at Work
If we wanted to create a whole population of
brainy people, we could take some people.
Have them mate.
Then have the brainiest offspring mate amongst
each other, and for countless generations keep
doing the same thing.
After 200 years, what would the population be like
or what are the chances that the 40th generation of
offspring be brainy?
Genetic Diversity
• The best source of genetic
diversity comes from
genetic mutations and new
gene combinations
produced at each human
conception.
• A mutation is a random
error in gene replication
that leads to a change.
Look at our Behaviors…
Can you answer these questions using evolutionary
psychology?
• Why do infants fear strangers when
they become mobile?
• Why are most parents devoted to their
children?
• 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?
Of course, there are other differences…
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
What do men and women want?
(According to Evolutionary Psychology)
Men want:
• Healthy
• Young
• Waist 1/3
narrower than
hips (a sign of
future fertility)
Women want:
• Wealth
• Power
• Security
Can this change?
Nature v. Nurture
What do you think so far?
Does Nature and Nurture interact
and grow off of each other?
Lets find out by examining Nurture in detail…
Environmental Influences on Behavior
Types of Environmental Influences
Parents
Prenatal
Experience
Peer Influence
Culture
Gender
How Much Credit (or Blame) Do
Parents Deserve?
•You and your siblings grow up in
the same environment, are you all
the same?
•Parents effect your belief
systems and values much more
than your personality.
•Parents take too much credit
for success and too much blame
for failures.
Are children clay to be
molded by their parents?
Lets look at perhaps our first environmental influence….
Prenatal Environment
Placental Arrangements in Identical
Twins: 2/3 share the same placenta.
Experience and Brain
Development
Parents spend a lot of
$$$ sending kids to
pre-school.
They just play with a
lot of toys.
The parents could use
that $$$ for a big flat
screen TV.
Is it money well spent?
Brain cells in an impoverished environment =
fewer synapses!
Brain cells in an enriched environment =
Leads to more synapses!
What does this mean for humans?
• If children from impoverished
environments are given stimulating
infant care, they score better on
intelligence tests by age 12 than
counterparts.
Use it or lose it!
A Trained Brain
A well-learned finger-tapping task activates more
motor cortex neurons (right) than were active in the
same brain before training (left).
Perhaps the biggest environmental influence, at
least by your age may be….
Peer Influence
•A mom can’t get her child to
clean up her toys, but when the
child sees her friends clean up
in school, she jumps to it.
•“Selection effect” - we seek
out people with similar
interests - that may explain
why we seem to conform to our
peers.
Culture
• Behaviors, attitudes,
traditions, etc… of a
large group passed
down from one
generation to the next.
Cultural Variations
• It is important to recognize our cultural norms: an
understood rule for acceptable behavior.
• Individualistic (independent selves) vs. Collectivist
Cultures (interdependent selves).
• Cultural differences appear in things like
punctuality, personal space, show of emotions, etc.
Variations over Time
• Different generations of the same culture
may also have differing norms.
Memes
• Self-replicating ideas, fashions or innovations
passed from person to person.
“Where’s the Beef” Lady.
McDonald’s Catch Phrases
Viral Internet Memes like Planking
Gender
• We already know the
nature differences.
• XX vs. XY
• But that focuses on SEX.
• We are going to discuss
GENDER: What is the
difference?
Gender Roles
• A set of expected
behaviors for
males and females.
• What are some of
your gender roles?
What traditional gender role is she breaking?
Changing Attitudes about Gender Roles
Gender Identity
• Our own sense of male or
female.
• Personalized to us.
• We realize our gender identity
through gender-typing: the
acquisition of a traditional
masculine or feminine role.
Two Theories of Gender-typing
Social Learning Theory
Dad plays
baseball.
Wife puts on
makeup.
Son imitates behavior.
Son copies her.
Dad rewards son.
Dad punishes son.
Gender Schema Theory
• Schema: a concept or framework of how we organize
information.
• We develop schemas for gender which becomes the lens
through which you view your experiences.
• That concept then influences your perceptions and behavior.
Boy’s don’t do this,
that’s for girls.
Yeah, that’s cool!!!!
I want to do that.