Nature,
Nurture,
and
Human
Diversity
Modules
11, 12, 13
Evolution
Why Do We have Sex?
• Asexual reproduction is simpler (just divide in
half and grow)
Why spend time and energy on sex?
• Bacteria and viruses change very fast
Able home invaders---can quickly pick your
locks.
• What to do? Spin your protein dial.
Mix your protein profile with someone else on
every replication
"Protein profile mixing"
• Shuffling genes (sex) raises survival odds
against parasites enough to offset its energy
costs
How did you get the way you are?
1. Designed by a supernatural being?
Evidence of complex design proves
existence of God?
Scientists reject "Intelligent Design" theory
of organisms (poor logic, zero evidence)
Science ignores non-material hypotheses
(because of Occams Razor, and/or
untestability, and/or lack of
conscilience)
2. Planetary seeding theory?
"On the Origin of Species" (1859)
Evolution by natural selection
Complexity emerges very gradually from:
• Natural selection on random genetic
mutations (e.g., color vision)
• Sexual selection on random genetic
mutations (e.g., peacock's tail, maybe our
overly large brain too!)
Natural Selection
• The evolutionary process by which some genes in
a population spread more than others do, causing
species to change over time.
Differential reproductive success from inherited
variants" -Darwin
Principles of Natural Selection:
• Within species variability, no two organisms are
identical.
• Variants differ in suitability
• Those better suited will reproduce more.
• Therefore, those genes rise in frequency in the
gene pool.
Evolution
Mutations
• Random gene copying errors that create
genetic variation
Adaptations
• When random genetic copying errors cause
changes in the phenotype that improve
replication chances
Grant and Grant (1989)
Natural selection of
thick beaks after a
severe drought
Evolution
Overwhelming physical evidence
• Fossil record
• Homology (similar structures)
forelimb of bats and whales
• Analogy to selective breeding
Domestication of foxes (Russian
experiment)
• Direct observations (Grants' finch study)
• Genomics evidence (overwhelming)
Pope recently agrees: evolution is proven
What percentage of members
of the National Academy of
Science believe in God?
A.
B.
C.
D.
97%
70%
31%
6%
Evolutionary Psychology:
Understanding Human Nature
Some topics:
 Natural selection and
adaptation
 Evolutionary success may help
explain similarities
 An evolutionary explanation
of human sexuality
Evolutionary
psychology is the
study of how
evolutionary
principles help explain
the origin and
function of the human
mind, traits, and
behaviors.
We have been talking so far about
human differences; we may now
seek insight in the ways in which
humans are alike.
16
How might evolution have shaped
the human species?
Example:
 Why does “stranger anxiety”
develop between the ages of 9
and 13 months?
Hint: in evolutionary/survival
terms, humans are learning to
walk at that time.
Possible explanation: infants
who used their new ability to
walk by walking away from
family and toward a lion might
not have survived to reproduce
as well as those who decided to
cling to parents around the
time they learned to walk.
17
Evolutionary Psychology’s
Explanation of Phobias
 Why do people so easily
acquire a phobia of
snakes?
 An evolutionary
psychologist would note
that snakes are often
poisonous…
so those who more readily
learned to fear them were
more likely to survive and
reproduce.
 Can we apply the same
logic to phobias about
heights? enclosed
spaces? clowns?
18
Fore tribe, Papua New Guinea
Ekman & Friesen
(1974)
Joy
Anger
Disgust
Sadness
Moral foundations Theory
Haidt & Joseph (2001)
L
1) Care
from kin altruism
2) Justice
from reciprocal altruism
3) Authority
from dominance hierarchies
4) Loyalty
from group proximity, attachment
5) Purity
C
from disgust, e.g., contamination avoidance,
boundary vigilence, boundary protection
Parental Investment Theory
(Trivers, 1970s)
The sex that has a larger investment
(pregnancybirthnursing) is more
picky about partners
Female DNA replication favors cautious, choosy
copulation strategy (courtship, commitment)
Male DNA replication favors opportunistic,
unselective copulation strategy (sex, exit)
Gender Differences in sexuality
• Levels of investment / commitment
• Mate preferences (beauty, resources)
• Differences on sexual jealously
Frequency of Masturbation
50
45
40
35
30
25
20
15
10
5
0
Males
Females
Never
Few/mo
Few/wk
Daily+
Sex Differences in Desire for
Sexual Variety
Do you ever think of some else
during sex with your partner?
40
35
30
25
Males
Females
20
15
10
5
0
Never
Seld.
Occa.
Often
Alwys
Clark & Hatfield (1989)
80
70
60
50
Males
Females
40
30
20
10
0
Date
Apartment
Sex
Which would upset you more?
A
You discover your partner is
having sex with someone else.
B
You discover your partner has
fallen in love with someone else.
Sex differences in sexual jealousy
Critiquing Evolutionary Psychology
“You’re just
taking current
reality and
constructing a
way you could
have predicted
it.” This is
hindsight
reasoning and
unscientific.
Response: yes, but there
are predictions made
about future behavior
using this reasoning.
“You’re
attributing too
much to genes
rather than the
human ability to
make choices
about social
behavior.”
Response: yes, but our
evolutionary past does not
prevent our ability to act
differently; “is” does not
equal “ought.”
Nature/Nurture
From Genes to the Role of Environment
 How environment/experience affects brain development
 Forces guiding the course of development:
 parents
 peers
 culture
Our starting picture
Our environment gives us
our experiences.
Experience and Brain Development
Rats living in an “enriched” environment (more
social interaction and physical play) experienced a
greater growth in brain size and complexity than
those rats living in an “impoverished” environment.
Brain Development Means
Growth AND Pruning
 To make our well-used brain
pathways work better, the
unused connections are
“pruned” away.
 This means that if certain
abilities are not used, they
will fade.
Impact of Experience/Nurture on
Brain Development
The Process Continues into Adulthood
Repeated practice at
a finger-tapping task
begins to activate a
[slightly] larger group
of motor neurons.
Is parenting a powerful
environmental influence on
development?
 Generally,
environmental
influences, including
parenting, account for
about 10 percent of
temperament, but is
larger for values/habits.
 Non-abusive “average”
parents should ease off
on both the blame and
the credit they assume
for how their kids turn
out.
Where this percentage increases:
“extreme” parenting, including
severe neglect and abuse
Peer Influence
 The degree of peer influence is hard to trace. Apparent
conformity (the whole group smokes) could be a selection effect
(they get together because they want to be with others who like
to smoke).
 Interaction with peers can teach new social skills.
 Parents may try to have indirect influence by selecting a child’s
peers, such as by selecting a school or neighborhood. However,
ultimately, most children self-select their peers.
Parents vs. Peers
Battling over non-genetic influence
Parents have more
influence on:
Education and career path
Cooperation
Self-discipline
Responsibility
Charitableness
Religion
Style of interaction with
authority figures
Peers have more
influence on:
Learning cooperation skills
Learning the path to popularity
Choice of music and other
recreation
Choice of clothing and other
cultural choices
Good and bad habits
Macduff Everton/The Image Bank/Getty Images
Gender Development
 Sex
 In psychology, the biologically influenced
characteristics by which people define males and
females
 Gender
 Refers to the physical, social, and behavioral
characteristics that are culturally associated with male
and female roles and identity
 Our gender is the product of the interplay among our
biological dispositions, our developmental
experiences, and our current situation.
Differences Between Genders
Biological:
women enter
puberty
earlier, live
longer, and
have more fat
and less
muscle
Mental and Behavioral Health:
 women are more likely to have
depression, anxiety, or eating
disorders
 men are more likely to have
autism, ADHD, and antisocial
personality disorder
Gender and
Aggression:
 men behave more
aggressively than
women, and are
more likely to
behave in ways that
harm others
 this difference
applies to physical
aggression rather
than verbal or
relational aggression
Macduff Everton/The Image Bank/Getty Images
Gender Differences
 Gender and aggression
 Minor physical aggression: Men and
women equal
 Extreme violent acts: Men commit more
than women
 Relational aggression: Women more
likely than men
 Interaction style: Men offer opinions;
women offer support.
Gender and Social Power
 In a variety of cultures,
men have attributes
and reputations that
help them attain more
social power (positions
controlling more people
and resources) than
women do.
 Men tend to interact in
more dominating ways
than women. Men
often speak opinions
rather than offering
support and inviting
input as women do.
Gender and Social Connection: Play
 When boys play, the focus
tends to be on the activity.
 Male play is more competitive.
 Men tend to dictate how the
playtime will proceed.
 When women play, the focus
tends to be on connection and
conversation.
 Female play is more social.
 Girls tend to invite feedback.
Are these differences due to nature or nurture?
Gender and Social Communication
Women communicate
more than men:
 more time with friends
 more text messages
 longer phone calls
However, men and
women speak about the
same number of words
per day. What fills in the
extra time on those
longer phone calls?
Maybe….
listening?
Men and women use communication differently.
 Women seek input and
 Men state their opinions
explore relationships.
and solutions .
 Men speak about things and  Women speak about people
and feelings.
actions.
Gender and Social Connectedness
 Both men and women
turn to women when
they want someone
to talk to, seeking the
“tend and befriend”
response or better
listening.
 Women tend to have
stronger ties to
friends and family.
 Women are often
more involved with
religion.
The Nurture side of Gender Roles:
The Influence of Culture
Gender role: the behaviors
expected of people related to
their identity as men and
women
Gender identity: one’s sense of
whether one is male and female,
including a sense of what it means
to be that gender
Does culture define which behaviors fill a gender role?
Or do the roles affect culture?
Gender roles and culture: is differentiation a good thing?
If it’s man’s job to get
the high paying
employment,
If it’s women’s work
to take care of the
kids and home,
 does that prevent conflict, and help culture stay stable,
because roles are clear?
 or is equality worth having some conflict and uncertainty?
Change in Social Roles?
If current trends continue, women will soon be the
majority of practitioners in some fields that were once
dominated by men in the United States.
Culture Influence
on Gender Role Development
Or is it instinct?
 Social learning theory: learning (by
imitation and conditioning) through
soc. observ. & interaction
 Gender schemas: mental categories
and expectations; they guide our
perceptions
 Gender typing: the innate drive to
identify with & conform to gender
roles
3 Influences on Who You Become
Beyond Biopsychosocial Influences:
CHOICES
 Is our behavior and identity rigidly
determined by our combination of
nature/genes and nurture/experience?
We can make choices that override our
genetic influences, that differ from cultural
norms, and that do not fit our environment.
We can even choose to directly alter
culture, environment, and even genes.
Culture Influences on Development
Culture and the self: individualism and collectivism
 Individualist cultures value independence. They promote personal
ideals, strengths, and goals, pursued in competition with others,
leading to individual achievement and finding a unique identity.
 Collectivist cultures value interdependence. They promote group
and societal goals and duties, and blending in with group identity,
with achievement attributed to mutual support.
Individualist and Collectivist Cultures Compared
Culture Influences on Development
Similarities across groups
 Although there are cultural differences, the differences within any
group are usually greater than the differences between groups.
Example: How socially active are people in people in two
hypothetical countries? They may differ on average because of
cultural influence, but both countries may have many mildly friendly
people.
Sociability Levels in Shyland
Sociability Levels in Partyland
SCALE: Self-Isolating -- Shy --
Private -- Friendly -- Outgoing -- Partier
Level/Amount of Social Activity
Culture and Genes:
A Complex Interaction
 There is a difference in average
blood pressure between
“racial” groups.
 This may seem like a genetic
difference but may actually be
a cultural difference…. How?
Different cultures may
have dietary
differences, which in
turn affect blood
pressure.
Child-rearing: Cultural Differences
 People in individualist
cultures might raise
children to be self-reliant
and independent.
 People in collectivist
cultures might raise
children to be compliant,
obedient, and integrated
into webs of mutual
support.
 People in Asian and
African cultures might
raise children to be more
emotionally and
physically close to others
than in western
European cultures.
Please ignore the remaining slides here. Information
on them will not be examined on in the December
exam (i.e, Test 3).
Regarding the Intelligence chapter (modules 29, 30, 31,
32):
Those 4 modules of the Intelligence chapter are required
textbook reading for Test 3 but there will not be any
slides posted for that chapter because we did not lecture
on that chapter in class. Only the textbook information
will therefore be required for that chapter.
Sexual Differentiation (6th wk)
All born with:
Primordial Gonad
Mullerian tissues (fem. reprod system)
Wolffian tissues (male reprod system)
Only difference is: Y chromosome
Week 6, the magic begins
Y starts producing… H-Y
Antigen
Sexual Differentiation
th
(6
week)
H-Y antigen…
• Mullerian withers away….
• Primordial gonad--> testes
• Testes--->Testosterone (Androgens)
Binds to androgen receptors.
Switches on male development.
MASCULINIZATION
Sexual Differentiation
Q: If a female (XX) fetus was exposed to high
levels of testosterone what might occur?
Partial masculinization
Clitoral hypertrophy, ambiguous genitalia
AGS (Adrenal-Genital Syndrome)
Money & Erhardt (1966)
AGS girls followed over time
Male playmate & toy preferences
Sexual Differentiation
Q: If a male fetus (XY) lacked an enzyme
required to “recognize” androgen
hormones, what might occur?
No masculinization.
Completely female
AIS
Androgen Insensitivity Syndrome
1/ 13,000 births
Human Connectome Project
Pink
= Corpus Callosum circuits connecting hemisph.
Green = Frontal Lobe circuits going to Hippocampus
Structural Connectome by gender
on a very large population (949) youths.
RESULTS
M optimized for intrahemispheric communication.
F optimized for interhemispheric communication.
Shows up very early ages
Wide differences by adolescence and adulthood.
CONCLUSION
1. MALE brains are structured to facilitate connectivity between
perception and coordinated action
2. FEMALE brains are structured to facilitate communication between
analytical and intuitive processing modes.
Sex Differences in aggression
Sex differences in
aggressiveness
emerge by age 3
Homicide Rates (/million)
Gender Segregation in Employment
Lubinski, Benbow, Kell (2014)
 How do math whiz kids turn out?
 Top 1% girls and boys in the nation.
 Were career outcomes
the same for girls & boys?
Lubinski, Benbow, Kell (2014)
STEM fields
Lubinski, Benbow, Kell (2014)
Gender difference in work preferences
Lubinski, Benbow, Kell (2014)
Gender difference in life values
Lubinski, Benbow, Kell (2014)
Gender difference in Personal Views