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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 most cells we have 46 chromosomes…
Except…
Sperm and Eggs
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 I’m genetically related to all of the
People in this photo  My dad and
dominant and
Grandfather used to have brown hair,
“overrides” the
But then I came along and made them
recessive gene.
Go gray. The gene for brown hair is
Dominant, which is why I’m not
Blonde like my mom.
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?
• Because my dad has green eyes, and
my mom has blue I was genetically
predisposed to have blue eyes.
Other Dominant Traits
• Curly hair.
• Unattached earlobes.
• Farsightedness.
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.
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.
•
http://www.youtube.com/watch?v=qw3S35wGgT8
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
• The goal of
human behavior
is to perpetuate
the gene pool.
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!
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…