Human Behavior
Nature vs. Nurture
Nature or Nurture?
Why do men and women have such
different attitudes about sex?
 Why do boys and girls play with different
toys?
 Why do you, the oldest, seem to be
organized and responsible, while your
youngest brother seems to be carefree
and happily irresponsible?

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
Nature and Gender

Gender Development
What determines male, female offspring
23rd pair of chromosomes determine sex
Female=X, Male = X or Y
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?
Gerald Levy and Mark Newman
Bouchard Minnesota Twin Study
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…
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
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?!?!
Evolutionary Psychology

Premise
 (Darwins’ ) natural
selection shapes
our behavior,
thinking (over time)
 Certain traits,
behaviors that
enhance survival
are passed on over
generations
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?
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 an
adaptive advantage,
those traits will prevail
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
Boys, girls and toys…
Nature or Nurture?

Why do genders choose what they do…?
Nurture and Gender
Nurture influences our sense of gender
by…
Gender identity (one’s sense of being male or
female)
 Gender roles- traditional behaviors, duties of
genders
 Gender-typing: expectation or assignment of
traditional male, female roles


Social learning theory (Observation, imitation)
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.)
Nurture and Early 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
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