 Nature, Nurture, and Human Diversity
Chapter 4
 Nature, Nurture, and Human Diversity
What causes our striking diversity in
psychological functioning, and also our
shared identity?
Credit: Kjetil Ree
People differ in many
aspects of psychological
functioning. For example,
some people possess a
“Type A” personality and
are aggressive, ambitious,
and controlling, whereas
others possess a “Type B”
personality and are passive
and easy-going.
People differ in many
aspects of psychological
functioning. For example,
some people possess a
“Type A” personality and
are aggressive, ambitious,
and controlling, whereas
others possess a “Type B”
personality and are passive
and easy-going.
People differ in many
aspects of psychological
functioning. For example,
some people possess a
“Type A” personality and
are aggressive, ambitious,
and controlling, whereas
others possess a “Type B”
personality and are passive
and easy-going.
Credit: Luca Galuzzi
Yet, we are also similar in
some aspects of our
psychological functioning.
For example, whether we
live in the Arctic or tropics,
we divide the color
spectrum into similar
colors.
Farbentafel, Wilhelm von Bezold
 Nature, Nurture, and Human Diversity
Behavioral Genetics
The study of effects of
environmental and genetic
factors, and their interplay, on
differences in psychological traits
 Nature, Nurture, and Human Diversity
Behavioral Genetics
Genes: Our Codes for Life
Genes: Our Codes for Life
Every cell in your
body contains
chromosomes—23
donated from your
mother, and 23 from
your father.
Genes: Our Codes for Life
Each chromosome is
made up of two
strands of DNA
connected in a double
helix. Genes are small
segments of DNA
molecules.
Genes: Our Codes for Life
James Watson and Francis Crick with their DNA model at
the Cavendish Laboratories in 1953. Photograph copyright
A. Barrington Brown.
 Nature, Nurture, and Human Diversity
Behavioral Genetics
Twin and Adoption Studies
Identical Versus Fraternal Twins
Credit: Derek Oliver (AP)
Identical twins develop from a single fertilized egg and are
genetically identical, whereas fraternal twins develop from
separate fertilized eggs and share half their genes, just like
siblings.
Identical Versus Fraternal Twins
Identical Versus Fraternal Twins
Correlation Between IQs of Family Members
Identical twins reared together
Fraternal twins reared together
(Bouchard & McGue, 1981)
.86
.60
Separated Twins
Even identical twins
separated at birth and
raised apart tend to be
more similar in their
psychological makeup
than fraternal twins.
Credit: Bob Sacha
Separated Twins
Credit: Bob Sacha
Jim Lewis and Jim
Springer, identical twins,
first met at the age of 39.
Lewis was a security.
guard, Springer a deputy
sheriff. Both married, and
divorced, a woman
named Linda—and
remarried a Betty.
Separated Twins
Lewis had a son named
“James Alan” and
Springer a son named
“James Allan”—and both
shared a taste for Miller
Lite and enjoyed
watching Nascar.
Credit: Bob Sacha
Separated Twins
Separated Twins
Personality, Intelligence
Abilities, Attitudes
Interests, Fears
Brain Waves, Heart Rate
Obviously, some of
these similarities are
pure coincidence. But
research has revealed
that identical twins
separated at birth are
indeed more similar to
less genetically-related
pairs in a number of
traits.
Biological Versus Adoptive Relatives
Are adopted children
more alike their biological
parents, who contributed
their genes, or their
adoptive parents, who
contribute a home
environment?
Biological
Versus Adoptive
Adoptive Relatives
Biological
Versus
Relatives
Correlation Between IQs of Family Members
Child and biological parent by whom child is reared
.42
Child and biological mother separated from the child by adoption .31
Child and unrelated adoptive mother
.17
(Horn, Loehlin, & Willerman, 1979)
Surprisingly, in many traits, adoptive children do not closely
resemble their adoptive parents and are more similar to
their biological parents.
 Nature, Nurture, and Human Diversity
Behavioral Genetics
Heritability
Correlation Between IQs of Family Members
Identical twins reared together
Fraternal twins reared together
.86
.60
(Bouchard & McGue, 1981)
Heritability (denoted h2) of a trait is a mathematical
estimate of the extent to which variation among individuals
can be attributed to their differing genes; it can range from
0 to 1.
http://www.cnn.com/videos/world/2015/07/10/two-sets-of-twins-switched-at-birth-silverstein-intvnr.cnn/video/playlists/thats-pretty-cool/
Group Differences
A trait can be found to
be substantially
heritable, but this does
not imply that group
differences, such as
those between men
and women, are
heritable.
Group Differences
 Nature, Nurture, and Human Diversity
Behavioral Genetics
The New Frontier: Molecular
Genetics
The goal of molecular
genetics is to identify
specific genes that
influence behavior.
The APOE4 gene has
been linked to Alzheimer’s
Disease, which both
Ronald Reagan and
Charlton Heston
developed.
Credit: White House Photo Office
The ACTN3 gene has
been linked to high-level
success in sprinting—a
possible “gene for speed”
The sample included 107
athletes from short-distance
events in track, swimming,
cycling, and skating, as well as
nine judo athletes. Compared
to 18 percent of control
subjects, only 6 percent of
these athletes—and none of
the thirty-two Olympians in the
sample—had a variant of
ACTN3 that made them alphaactinin-3 deficient.
 Nature, Nurture, and Human Diversity
Evolutionary Psychology
By virtue of a common ancestral
history, how are humans alike?
Charles Darwin
From collection of Henry Maull and John Fox
Natural selection:
Organisms’ varied offspring
compete for survival.
Certain behavioral
characteristics increase
odds of survival in a
particular environment.
Offspring that survive
reproduce and pass on
their genes.
Over a 40 year span,
Dmitry Belyaev and
colleagues in Russian
produced a breed of foxes
that are “docile, eager to
please, and unmistakably
domesticated.”
Over a 40 year span,
Dmitry Belyaev and
colleagues in Russian
produced a breed of foxes
that are “docile, eager to
please, and unmistakably
domesticated.”
http://www.youtube.com/watch_popup?v=GjqkBcZLwVY&vq=medium
Credit: Tom Adriaenssen
Evolutionary psychologists
believe our tendencies as
humans have been
shaped by evolution. For
example, some women’s
experience of nausea in
the first three months of
pregnancy predisposes
them to avoid foods that
may be toxic to the fetus.
Gender Differences in Sexuality
Have different
adaptive challenge for
men and women led
to gender differences
in psychological
functioning?
The Meeting Place, Paul Day
Credit: Oxyman
Gender Differences in Sexuality
Evolutionary psychologists
believe the answer is yes.
Men are responsible for
spreading genes, and
across cultures, they are
found to be more likely to
initiate sex than women,
and to desire and think
about sex more than
women.
The Meeting Place, Paul Day
Credit: Oxyman
Gender Differences in Sexuality
Also, across cultures,
men judge women as more
attractive if they have a
youthful appearance.
According to evolutionary
psychologists, this is
because young women
have a better chance of
conceiving than older
women.
Gender Differences in Sexuality
In the present experiments, male and
female confederates of average
attractiveness approached potential
partners (opposite sex) with 1 of 3
requests: “I have been noticing you
around campus. I find you to be very
attractive…
"Would you go out tonight?"
"Will you come over to my apartment?"
"Would you go to bed with me?"
Gender Differences in Sexuality
Type of Request
Confederate - Subject
Male asking Female
Female asking Male
Date
Apt.
Bed
Gender Differences in Sexuality
Type of Request
Confederate - Subject
Date
Male asking Female
56%
Female asking Male
50%
Apt.
Bed
Gender Differences in Sexuality
Type of Request
Confederate - Subject
Date
Apt.
Male asking Female
56%
6%
Female asking Male
50%
69%
Bed
Gender Differences in Sexuality
Type of Request
Confederate - Subject
Date
Apt.
Bed
Male asking Female
56%
6%
0%
Female asking Male
50%
69%
75%
Gender Differences in Sexuality
Type of Request
Confederate - Subject
Date
Apt.
Bed
Male asking Female
56%
6%
0%
Female asking Male
50%
69%
75%
Gender Differences in Sexuality
In general, the female experimenters reported that men were at
ease with the request. They would say “Why do we have to wait
until tonight?” or “I cannot tonight, but tomorrow would be
fine.”…In contrast, the women’s response…was “You’ve got to
be kidding,” or “What is wrong with you? Leave me alone.”
Gender Differences in Sexuality
Type of Request
Confederate - Subject
Date
Apt.
Bed
Male asking Female
50%
0%
0%
Female asking Male
50%
69%
69%
(1982 Replication)
 Nature, Nurture, and Human Diversity
Parents and Peers
Parents and Early Experiences
Experience and Brain Development
Whether early environment is impoverished or enriched
has a major impact on brain development: Rosenzweig and
Krech found that rats raised in an enriched environment
developed a larger, and thicker, cortex than rats raised in
an impoverished environment.
Experience and Brain Development
A trained brain: A
well-learned fingertapping task, practiced
thousands of times,
activates more motor
cortex neurons (in
orange) than were
active in the same
brain before training.
Experience and Brain Development
This same sort of brain
plasticity is seen in
humans. In one study,
researchers found that
London taxi cab drivers
had larger hippocampal
brain regions responsible
for spatial memory than
did controls.
Credit: Andreas Tusche
How Much Credit (or Blame) Do Parents Deserve?
Parents do matter,
especially at extremes.
For example, abused
children are prone to
abuse their own children
as adults. Somewhat
surprisingly, however,
shared environmental
influences on personality
and intelligence are fairly
small (around 10%).
How Much Credit (or Blame) Do Peers Deserve?
Credit: Ole Graf/zefa/Corbis
There are large
influences of peers on
a variety of behaviors
and traits. Psychologist
Judith Rich Harris
concludes that peers
play a larger role in
shaping personality
than do parents.
 Nature, Nurture, and Human Diversity
Cultural Influences
Culture: Behavior, ideas,
attitudes, values and traditions
shared by a group transmitted
from one generation to the next
Credit: Bart Swanson
Many other animals are
social. However, nearly
all other animals lack the
means to preserve
innovations, and in so
doing, to build a culture.
What separates humans
from all other animals is
mastery of language.
Credit: HawaiianMama
Wolves, for example,
are social animals, and
yet they function
almost exactly as they
did 10,000 years ago.
By contrast, on an ever
day basis, you and I
use technologies that
were unimaginable
only a century ago.
 Nature, Nurture, and Human Diversity
Cultural Influences
Variation Across Cultures
Each cultural group has
norms—rules for expected
and accepted behavior. For
example, cultures differ in
norms regarding personal
space—the portable buffer
zone we like to maintain
around our bodies. North
Americans tend to prefer
more personal space than
do Latin Americans.
Credit: GodShiru
Credit: Yoichi R. Okamoto
And when our personal
space is invaded, we feel
uncomfortable. Lyndon
Johnson was known to be
a “close talker,” perhaps as
a means of intimidation.
At left, Senator Richard
Russell receiving the
“Johnson treatment.”
https://www.youtube.com/watch?v=NGVSIkEi3mM
 Nature, Nurture, and Human Diversity
Cultural Influences
Variation Over Time
As case in point, consider
cultural changes in the
United States since the
1960s. Some changes are
positive. Women are more
likely to marry for love than
out of economic need, and
rights of minority groups
have expanded. But some
are negative. There is
more divorce, delinquency,
and depression.
 Nature, Nurture, and Human Diversity
Cultural Influences
Culture and the Self
Credit: Kevin R. Morris
Cultures vary in the extent
to which they give priority to
the expression of personal
identity or group identity.
Cultures that give priority to
the independent self are
high in individualism, while
those that give priority to the
interdependent self are high
in collectivism.
Differences in individualism
vs. collectivism influence
how we make attributions
about our success and
failures.
Credit: Martin Dougiamas
The boarding school model of child-rearing
Differences in individualism
vs. collectivism also have
an influence on child-rearing.
Many Asians and Africans live
in cultures that greatly value
emotional closeness, whereas
Westerners place a greater
emphasis on development of
independence.
 Nature, Nurture, and Human Diversity
Gender Development
Gender Similarities and
Dissimilarities
Much is made about
differences between
males and females in
the popular press, and
there are some striking
differences. Women
have a keener sense of
smell than men, and are
twice as vulnerable as
men to depression and
anxiety. And girls tend
to be more cooperative
and less competitive in
their play than boys.
On the other hand, men
are more prone to
physical aggression
than women (the maleto-female arrest ratio in
the United States is 10
to 1), and are more
dominant, forceful, and
independent than
women.
However, some of the most talked about gender
differences are actually quite small. For example, the
average difference between females and males in
self-esteem is only about .2 standard deviations.
Credit: Jagger
And other much talked-about gender differences are
not substantiated by scientific evidence. For
example, despite the popular belief otherwise, there
appears to be no evidence that women are better at
multitasking than men.
 Nature, Nurture, and Human Diversity
We are the product of nature and nurture. Genes
are all-pervasive but not all-powerful. Culture is allpervasive but not all-powerful.
 Chapter Review
What does the subfield of behavioral
genetics focus on?
What do evolutionary psychologists
study?
What is known about peer versus parent
influences on traits?
What is known about gender differences
and similarities?
 Chapter 4 Review
Question(s) from textbook on material
not covered in class:
Gene-Environment Interaction