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 SimilaritiesMr. Goode is

95%

99.9%

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 Females-

mated - 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…

• 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?

Can you answer these questions using evolutionary psychology?

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?

Are children clay to be molded by their parents?

•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.

Prenatal Environment

Lets look at perhaps our first environmental influence….

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).

Peer Influence

Perhaps the biggest environmental influence, at least by your age may be….

•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.

Viral Internet Memes like Planking

“Where’s the Beef” Lady.

McDonald’s Catch Phrases

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.

Son imitates behavior.Dad rewards son.

Wife puts on makeup.

Son copies her.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.