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
Just how similar are we?
(True or False)
1. Fraternal twins are no more genetically similar
than normal siblings.
2. If after a worldwide catastrophe only
Icelanders or Kenyans survived, the human
species would suffer a huge reduction in its
genetic diversity.
 We share 99.9% of our DNA with our
neighbor! (Near clones!)
 “We are the leaves of one tree.”
Nature, Nurture and Human
Diversity
Essential Question: What ultimately
shapes our behavior?
Topics of Study:
Genetics and Evolutionary Psychology
Parents, Peers and Culture
Gender
Pattern Recognition

Nature v. Nurture
1.
Sugar and spice and everything nice, that’s what little
girls are made of…”
“Handsome is as handsome does.”
“Like father like son.”
“You can’t teach an old dog new tricks.”
“Boys will be boys.”
“You are what you eat.”
“Blood will tell.”
“All men are created equal.”
2.
3.
4.
6.
7.
8.
9.
Genetics and Behavior
Getting started…..
We know that both nature and nurture
weave together to shape our behavior.
Its easy to prove that nurture influences
behavior, but how could we devise a way
to prove that genetics influences our
behavior?
Read carefully pages 95-102
1. Identify the following and explain how they
collectively influence behavior.
chromosomes, DNA, genes, gene complexes
2. Explain specifically how studies contrasting
fraternal and identical twins have helped
prove that genetics influence individual
behavior.
3. The case studies of Jim Lewis / Springer and
Oscar Sohr / Jack Yufe (identical and
separated at birth) provide evidence that
genetics influence’s behavior. Explain
specifically the strengths and weaknesses of
these studies.
Behavior Genetics

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 (no more genetic
similarity than normal
siblings)

Identical:
(Monozygotic)
 Single fertilized egg
split in two = clones
Fraternal vs. Identical
Fraternal v. Identical
Fraternal vs. Identical

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?
Twin Studies
Jim Lewis / Springer

What does the study suggest?
Jim an Jim
37 days after birth
 Romantic- love notes to wife
 Son James, dog Toy, wife Linda
 Woodworking (same bench in front yard)
 Chevy, stock car racing, Miller Lite
 Vasectomy, high blood pressure, chain
smoker
 migraines

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
Adoption, Genetics and Behavior
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
Temperament

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.
Heritability

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
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

Identify specific genes
influence on behavior
 Weight, extraversion,
sexual orientation…
 LD, depression,
schizophrenia,
alcoholism…
 Designer babies?!?!
Questions to Consider
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…….
Evolution and Human Sexuality
True or False:
Males are more likely than females to initiate sexual activity.
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
Question: Why is there a difference between genders
concerning attitudes and behaviors about sex?
Gender Differences and Sexuality
Natural Selection

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 and Attraction
Study spanned 37 cultures

Men (attracted to…)
 Youthful, healthy,
fertile
 Waists 1/3 size of hips
 Many children- genes
to future…

Women (attracted to..)
 Mature, dominant, bold,
affluent
 Support and protect
 Long- term mating,
investment in jointoffspring
Gender Differences and Sexuality
Significance?
 “Nature selects behaviors that increase the
likelihood of sending one’s genes into the
future.”

In Conclusion…

4 important gender differences in human sexuality
(Comprehensive Study: Letitia Anne Peplau)
1. Men show greater sexual desire than women
2. Women tend to emphasize committed relationships as a
context for sexuality (more so than men)
3. Aggression is more closely linked to sexuality for men
than women (powerful, domineering, experienced,
individualistic)
4. Women’s sexuality shows greater plasticity (attitudes,
behaviors about sex more easily shaped by cultural,
social factors)
 Example: college (liberalizes women’s attitude towards sex more
than men’s)
 Chance of men identifying as gay or bisexual: x2
 Chance of women identifying as lesbian or bisexual: x900!
Evolutionary Psychology

From an evolutionary psychology
perspective, how might we explain
marriage?
Nature, Nurture and Gender

Gender Development
Male, Female- What’s the difference?
23rd pair of chromosomes determine sex
Female=X, Male = X or Y
Glad to be your gender?

Men
 X4 to commit suicide,
alcoholism
 Autism, color
blindness,
hyperactivity, antisocial
personality disorder

Women







70% more fat
40% less muscle
5 inches shorter
Puberty 2 years earlier
Live 5 years longer
X2 for depression, anxiety
X10 for eating disorders
Gender and Aggression

Males tend to be more physically
aggressive
Male-female arrest rate for murder
U.S. 9-1
Canada 7-1
Gender and Social Power

Universal pattern: Men are more socially
dominant
Men: as leaders- more direct, autocratic,
express opinions
Women: as leaders- more open, democratic,
offer support
Gender and Social Behavior

Males
 Individualists
 Boys: larger play
groups (activity focus)
 Male Answer
Syndrome
 Freedom, self-reliance

Females
 Interdependent
(relationships)
 Girls: smaller groups
(often one friend) less
competitive, imitate
social relationships
 85% of greeting cards!
 More religiously
oriented
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
Nurture and Gender
Gender identity
 Social learning theory
 Gender Schema theory: Learning theory +
cognition

Schema, or concepts are formed by genders
in developing stages- 1yr olds: voice gender
differences
lens through which they see the world
confirms roles
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.
Genes rule…??

In terms of personality, environmental
factors typically account for less than 10%
of children’s differences. (Key is how
parents and peers influence those traits.)
Parenting the Genetic Code

Explain how one might address the
following genetic traits for productive
outcomes…
1.
sluggish, unresponsive, temperament as
3 month old
Imaginative, slightly hyperactive, ADD
high school student
2.
What / Who has shaped you…?

List the eight behavioral traits that most
reflect your personality. For each, indicate
which of the following has been most
influential in shaping that trait.
Parents
Peers
Genes
Results? Which factor do you think
most influential?
Prenatal Environment

Studies indicate that identical twins who
share the same placenta are more similar
in psychological traits than those twins
that don’t.
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…)
Peer Influence

True or False
1.
“Preschoolers who disdain a certain food
despite parents’ efforts will often eat the food
at a table of peers who like it.”
A child who hears English spoken with one
accent at home and another in the
neighborhood and at school will invariably
adopt the accent of his peers and not his
parents.
2.
Parents vs. Peers

Parents
 Education
 Discipline
 Responsibility
 Orderliness
 Charitableness
 Dealing with authority

Peers
 Cooperation
 Popularity
 Styles of interaction
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