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Behavioral Genetics and Gender
AP Psychology
Myers, Ch. 3
What Makes You You?

Nature - Genetics



Genes
Heredity
Nurture –
Environmental
circumstances



Culture
Parents
Peers
Behavioral Genetics

The study of relative power and limits of genetic and
environmental influences on behavior

Studies the interplay of nature and nurture
Nature
Biological Influences
Biological Influences



Genes – units of DNA that carry hereditary information
DNA (deoxyribonucleic acid) –contains the genetic
info to make chromosomes
Chromosomes – threadlike structures made of DNA
that contain the genes (46, 23 pairs)
Biological Influences

Genome – the complete genetic instructions for making
an organism (shared genetic profile)


As humans we share 99.9% of the same DNA, but the 0.01%
difference is what makes us all different.
Humans and chimpanzees share about 95% of the same
DNA – close cousins, but clearly very different.
Twin Studies – Nature’s Perfect Experiment


Allows scientists to separate nature and
nurture influences
Same
sex only
Same or
opposite sex
Differences are due to environment
Fraternal twins – 2 eggs at the same
time genetically similar like any other sibling
relationship


Fraternal
twins
Identical twins – one egg split in two 
genetically identical


Identical
twins
Differences due to genetics and environment
Identical twins are MUCH MORE SIMILAR
in ALL AREAS than fraternal twins.



Intelligence
Predisposition to behaviors
Temperament – emotional reactivity,
influences personality (constant from infancy
to adulthood)
Twin Studies – Separating Nature and
Nurture



Identical twins separated at birth share overwhelming
similarities later in life.
Fraternal twins share some similarities but not close to
those of identical pairs.
Critics – place two strangers in a room and study them 
you will find dozens of similarities and coincidences as well
Twin Studies – Separating Nature and
Nurture
Same environment
Differences due to
nurture
Apart – different
environments
Differences due to
nurture
(resemble biological
parents)
Same
Environment
Differences due
to nature and
nurture
Apart – different
environments
Differences due
to nature and
nurture
Identical Twins
(genetically identical)
Fraternal Twins
(genetically
similar)
Heritability

The extent to which genetic individual differences contribute to individual
differences in observed behavior


Example - Mark Twain’s Idea…




“How much is this trait influenced by nature, rather than nurture?”
10 unrelated boys are raised until age 12 in barrels, thus experiencing
exactly the same environment.
When given an IQ test at age 12, their results will be lower than most
12 year old boys but relatively similar.
100% of any differences would be attributed to genetic influences and
heredity  Therefore, the heritability of intelligence would be 100% in
this situation.
Heritability percentages change as environmental and genetic factors
interact.


As environments become more similar, heritability increases.
As environments become more diverse, heritability decreases.
Nurture VIA Nature

Diathesis-stress model


Behaviors are a result of both biological (nature) factors and life experiences
(nurture).
Interaction

the effect of one factor (eg: environment) depends on another factor (eg:
heredity)

Some people are genetically predisposed/vulnerable to certain
conditions, which are then triggered by external circumstances.

EX: Schizophrenia



Nature – family studies show that schizophrenia is in part heritable
(family studies, 1/10 if parent has disease; 1/100 if not)
Nurture – stressful or traumatic events can trigger the onset of
schizophrenia
Other examples: obesity, heart disease, alcoholism, eating disorders
Evolutionary Psychology

Study of evolution of behavior and the mind



Natural selection –traits that enable survival and reproduction
will be passed to succeeding generations



How are we all alike?
Focuses on natural selection
Certain fears may be innate – humans who stayed away from
dangerous animals and plants survived (those who did not were
killed – no reproduction
Changes in traits over time are due to genetic mutations
While the theory of evolution is religiously contested, virtually
every scientist will agree with Darwin’s general theory
evolution through natural selection – basis of biology
Evolutionary Theories on Sexuality

Ever wonder why women may tend to view sexual
activity in terms of relationships while men may tend view
sexual activity in terms of recreation…

Historically, men and women worked together to ensure
the survival of the most offspring.


Women chose wisely to mate with one or a few strong healthy
men.
Men chose to mate with many women to increase the
possibility of healthy children.
Evolutionary Theories on Sexuality

What do men and women consider “attractive?”

Men – youthfulness and an hourglass figure (waist 1/3
narrower than hips.


Eludes to past generations of men looking for healthy women
to increase the chance of the offspring survival) – a woman
appears more fertile if their waist is 1/3 narrower than their
hips
Women – youthful/healthy looking, mature, dominant,
bold, affluent, and commitment-oriented

Eludes to past generations of women needing strong healthy
men to support and protect mother/child
Critics of the Evolutionary Perspective

Critics of evolutionary psychology – “Mental processes and
behaviors are also influenced by culture and society.”




Going back to sexuality as an example…
What men and women desire in each other changes with
culture and society


Culture dictates our choices, not just evolution.
Too much emphasis on nature, while ignoring nurture.
eg: Marilyn Monroe of the 1950s was considered the quintessential
sexy woman, however she weighed much more than what is
considered beauty in the 2000s
Culture dictates our mating choices, not just evolution

Culturally accepted in Western societies that humans pair off
monogamously, unlike thousands of years ago when men had sex
with various women to ensure the survival of their offspring.
Nurture
Environmental Influences
Prenatal Development

Mother's placenta gives fetus nourishment, as well as can
transfer toxic agents.

Why is this a nurture influence and not a nature influence?
Experience and Brain Development

Experience reflects on brain size and complexity (Rosenzweig
rat experiment)

Babies who are handled (especially premature babies) develop faster
than nonhandled babies. Evidence is found in prenatal units - mothers
hold premature babies to speed development and growth.
Impoverished
environment
 Use it or
Rat brain
cell
Enriched
environment
Rat brain
cell
lose it – stimulation is essential for brain
development and maintenance.

"Our genes dictate overall brain architecture, but experience
directs the details."
Parental and Peer Influence
Parents

LONG TERM INFLUENCE



Peers

abused more likely to abuse,
political attitudes, religious
beliefs, personal manners, habits
education, discipline,
responsibility, orderliness,
charitableness, and ways of
interacting with authority
figures.
Other environmental factors
are at play as well, so parents
can’t get 100% credit or blame.
SHORT TERM INFLUENCE



Conformity, desire to “fit in”
in the short-term
learning cooperation, desire
for popularity, inventing styles
of interaction among people
of the same age.
Parents and family have
more long term influence
GENDER DEVELOPMENT
A Study into Nature and Nurture Influences
Sex vs Gender
Nature

Sex – biological category
for males and females
Nurture

Gender – social category
influenced by culturally
assumed characteristics
for males and females
Sex (Nature)


XX – chromosome pair for biological female
XY – chromosome pair for biological male
Sex (Nature)

Testosterone

Sex hormone, larger
amounts in males and
stimulates…



growth of male sex organs in
the fetus
development of male sex
characteristics during puberty
Biology affects our assumption of gender

Ex: botched circumcision + female upbringing (estrogen
supplements, extreme female genderfication) = gender identity
confusion
Gender (Nurture)


Role - a set of expectations/norms about a social
position
Gender roles – expectations about males and females
should behave


Culturally bound
Time/context specific
Gender (Nurture)

Gender Identity - one's sense of being male or female

Develops early in life (before puberty)
Theories on Gender

SOCIAL LEARNING THEORY (of Gender) children learn social behavior by observing, imitating,
and then by being rewarded or punished


children learn gender roles from parents and peers by
observing and imitating behaviors and then experiencing a
reward or punishment
eg: "Big boys don't cry." - a young boy is socially punished for
crying because expressing emotion (crying) is not associated
with male gender roles  diminished behavior - no more
crying
Theories on Gender

GENDER SCHEMA THEORY - Children
form a concept about gender and adjust
behavior/thoughts accordingly  view world with
gender lens



Female schema – cooking, long hair, pink, teacher, skirt
Male schema – rough, blue, airplane pilot, pants, short
hair
Constant modification


Assimilation - interpreting new experiences in
terms of existing schemas
Accommodation - adapting current
understandings/schemas to incorporate new
information
Observation
Based on observation then
schema creation/modification -
Observation then experience
Based on reward/punishment -
Gender and Social Connectedness







Females tend to be more interdependent and social spend less time alone than males
Boys typically play together in large groups, while girls
prefer smaller groups with intimate discussion
Men emphasize freedom and self-reliance
Women are more open to spirituality
Women are more intimate than men with friends
Men like doing activities that are side-by-side, while
women prefer face-to-face
Women are more likely to turn to others for
support/help