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Human Behavior
Nature, Nurture and Human Diversity
Our behavior is often characterized
as “human nature.”
What do we mean by human nature?
 How might a psychologist go about
identifying the traits of human nature?

In a culture that emphasizes our differences,
we sometimes forget just how similar we
are…
Brainstorm and list all the universal behaviors (behaviors
shared among all cultures) that you can think of…
communicate both verbally and nonverbally
Enforce rules of etiquette
Avoid incest
Fear snakes / heights
Exchange gifts
Modesty in sexual behavior and bodily functions
Labor divided by age and sex
Men- more aggressive than women
Women provide more child care
Tools for work
Belief systems- death, disease
Plan for the future
Taboos- crimes and legal punishments
Marriage
Laugh / smile / mimic / joke / flirt / sympathize / tease / dance /
Music /Myths / folklore / poetry
Games
War
In a world of such diverse cultures, why
do so many universal behaviors exist?

Genetic similarities / shared DNA
Nature, Nurture and Human
Diversity
Essential Question: What ultimately
shapes our behavior?
Topics of Study:
The Influence of genes: Behavioral Genetics
Evolutionary Psychology and Natural Selection
Nurture and Early Development
Behavior Genetics
(Text Question #1)

Study individual behavioral differences. (weigh
effects of nature, nurture)
 Chromosomes: 23 / egg, 23 / sperm (threadlike
structures)
Composed of DNA (deoxyribonucleic acid)
Genes: 30,000 each / self-replicating units,
synthesize proteins, (the building blocks of
physical development
Gene complexes: many genes acting in concert

Genes: Influence physical make-up, intelligence,
aggressiveness, happiness etc.
Behavior Genetics
Fraternal, Identical Twins:
What’s the difference?

Fraternal: (dizygotic)
 Separate fertilized
eggs (50% shared
genes- no more
genetic similarity than
normal siblings)

Identical:
(Monozygotic)
 Single fertilized egg
split in two = clones
(100% shared genes)
Fraternal vs. Identical (#2)

Fraternal / Identical twin study findings- provide
specifics for the following:
 Alzheimer’s
 Identical =60% / Fraternal=30%
 Extraversion / neuroticism
 Identical more similar than fraternal
 Divorce rates
 Identical x5.5 vs. fraternal x1.6
 Schizophrenia
 50, 10, 3, 1 (identical, fraternal, sibling, stranger)

What are the limitations of these studies?
 Genetics or environment? How do we differentiate?
The Bouchard Minnesota Twin Study

“Are You a Natural”- (handout questions)
Gerald Levy and Mark Newman
Separated at Birth
Levy and Newman

Bouchard’s Minnesota Twin Study
 Reunited by shared acquaintance
 Upon meeting for first time:
 Same mustache, sideburns, glasses
 Levey: college degree in forestry- Newman planned to but worked for city
trimming trees
 Levey worked installing sprinker systems, Newman installed fire alarms
 Both were bachelors, same taste in women
 Both only drank Budweiser (pinky wrapped underneath can, crushed can
afterwards)
 Hunting, fishing, beach, John Wayne movies, pro-wrestling, Chinese food in
wee hours
 Volunteer firefighters
 Both raised Jewish, neither particularly religious
 When met- same remarks, at same time, same gestures- “spooky”
 He is he and I am I, and we are one…
Genetics and Behavior
Why has genetics not been given more consideration as a
determiner of personality and behavior?
 2nd ½ of 20th century: behaviorism’s dominance
 “Experience as primary architect of human behavior”
 “Invisible” genetics- can’t see, touch or remember the influence
 Determinism- “compromises free will”
 Nurture gives parents measure of confidence- “can control
outcome”
 Bad, ineffective behavior can be “unlearned”
 “Why bother?” Genetic argument reduces free will, cornered by
determinism
 “That boy was born to act that way!”
 Reality: Both play critical role in who you are!
Adoption Studies (#5)
What insight has adoption studies provided
regarding the influence of genetics on personality?
(#5)
Environmental relatives / biological Relatives
 Finding: subject’s personality reflected
biological relatives, even when adopted at
birth
 Conclusion: people who grow up together
don’t resemble each other in personality
 Why are two people raised together so
different???

Confirmation of genes impact on personality
Environmental Influence

So what traits does nurture influence?
Values
Manners
Faith / religion
Politics
Social views
Heritability (#6)

Extent to which difference between
individuals can be attributed to genes
As environments become more similar,
heredity as a source of difference becomes
more important (and vice versa)
Heritable differences don’t often translate to
group differences
Temperament (#7)

Our emotional excitability
Temperament traits tend to remain consistent
through life
Studies confirm
Genetic temperament helps form enduring
personality
Think of two examples of those you know.
Nature and Nurture

Genes are self-regulating (respond and
adapt to environment)

Individual differences almost always the
result of both nature and nurture
– “Gene and scene dance together”
– Or, “nurture works on what nature endows”
Molecular Genetics (#8)

Identify specific genes
influence on behavior
 Weight, extraversion,
sexual orientation…
 LD, depression,
schizophrenia,
alcoholism…
 Designer babies?!?!
Human Nature?
1.
2.
3.
4.
Why do infants start to fear strangers
about the time they become mobile?
Why are most parents so passionately
devoted to their children?
Why do so many more people have
phobias about spiders and snakes than
guns and electricity?
Why are men quicker to perceive
friendliness as sexual interest?
Evolutionary Psychology

Premise
 (Darwins’ ) natural
selection shapes
our behavior,
thinking (over time)
 Certain traits,
behaviors that
enhance survival
are passed on over
generations
Dmitry Belyaev: Domestication of Foxes
Belyaev’s Experiment







30 males, 100 females
Tamest 5% M, 20% F
30 generations
Complete domestication
Now sold as house pets
Implications?
When certain traits are
selected that give a
reproductive advantage,
those traits will prevail
Evolutionary Psychology

For the most part, evolutionary psychology
helps to explain our similarities.
(Universal behaviors)
 But
it also helps explain some key
differences…….
Gender and Sexuality
On the issue of sex, would you characterize
the attitudes and behaviors of men and
women to be generally the same, or
different? Explain and provide examples.
Gender and Sexual Attitudes / Behavior
Studies:

1978, FSU- research assistants / proposals for
casual sex with strangers
75% of men- yes
0% of women- yes
Questionnaire: casual sex with different partners
 48% of men- yes
12 % of women- yes


How can we explain this radical difference
in sexual attitudes between the genders?
Gender Differences and Sexuality
Natural selection would suggest that each gender pursued
attitudes and behaviors that perpetuated their survival, and
thus became part of our DNA over time.

Women- relational
 Incubates, nurses one
infant
 Wants protection,
assistance to ensure
child’s survival
 Chooses wisely

Men- recreational
 Perpetuate his genes
(spread his genes
through other females)
 Chooses widely
Gender Differences and Sexuality
Significance?
 “Nature selects behaviors that increase the
likelihood of sending one’s genes into the
future.”

Nature, Nurture and Gender

Gender Development
Male, Female- What determines the gender?
23rd pair of chromosomes determine sex
Female=X, Male = X or Y
Boys, girls and toys…
Nature or Nurture?

Why do genders choose what they do…?
Nature and Gender

Prenatal Months
 7th week: develop male, female anatomical
distinctions
 4th, 5th month: Ovarian hormones, testosterone
influence different brain development
 Studies
 Hines and Alexander: Texas A&M- Velvet monkeys
 1 day old infants: video: friendly face or mechanical mobile
 1 yr. old infants: films: faces or cars
 Evidence suggests cognitive differences upon
birth
Gender Differences and the Brain
New evidence: structural, chemical and
functional differences between genders and
brains
Females: thicker frontal lobe (verbal fluency)
Males: thicker parietal Cortex (space perception)
Potential need for sex-specific treatments for
addictions, depression, schizophrenia etc.
Nurture and Gender
Nurture influences our sense of gender
by…
Gender identity (culture’s sense of being male or
female)
 Gender-typing: casting, assigning traditional
gender roles
 Gender-Schema theory: mental associations we
make influence how we perceive gender in other
issues
 Social learning theory (Observation, imitation)

Nurture and Early Neural
Development

Early experience matters!
Fosters neural connections
Experience preserves activated neural
connections
Unused ones degenerate (pruning)
Excess “connectors” in youth make kids more
capable of mastering certain tasks.
Example?
Foreign language, (Accent and grammar) visual
perception, musical instruments
Rat Studies

Rosenzweig and Krech
 Isolated, impoverished vs. social, enriched environment
 Young rats

Findings:
 Obvious differences in behavioral activity and curiosity
 Heavier, thicker brain cortex (brain weight increased 7-10 percent
and # of synapses increased 20%!)
Impoverished
environment
Rat brain
cell
Enriched
environment
Rat brain
cell
Premature Babies

Neonatal units
Massage therapy stimulates growth
Speeds departure from hospital
Parent’s Influence
Genes determine human traits (personality)
 Parents’ influence helps determine how those
traits are expressed!

 “Genome gives the basic plot, the parent gives it its
tone, accent and emphasis.”
 IOW- “It starts with the kid, and the parents pick up
on it.”

Implications are huge for parenting… (shaping
genetic traits to be productive ones…)
Nurture’s Sway…
Cultural Influences

Individualism
 Self: Independent
 Life Task: Discover, express
one’s uniqueness
 What matters: Me,
personal achievement,
rights, freedoms, selfesteem
 Coping method: change
reality
 Relationships: Many, often
temporary, confrontation
acceptable
 Behavior: Reflects one’s
personality, attitude

Collectivism
 Self: Interdependent
 Life Task: fit in, perform
role, obligations
 What matters: Us, group
goals, family duty, social
responsibility
 Coping method:
Accommodate to reality
 Relationships: Few, close
and long term, harmony
valued
 Behavior: social norms and
roles
Cultural Influences

Individualism

Collectivism