Psychology 10th Edition David Myers

1
Chapter 4
Nature, Nurture, and Human Diversity
2
Overview Nature/Nurture/Diversity Questions

• How do we explain traits that all humans may have
  in common?
• How do we explain the origins of diversity, the
  source of differences in the traits
• between genders?
• among cultures?
• among individuals?
• But first, how do we investigate these issues?

3

• Genetics
• Branch of biology that deals with the mechanisms
  of heredity.
• Heredity
• Transmission of genetic information from one
  generation to the next
• Behavior Genetics
• Study of how variation in genes affects variation
  in behavior

4
Behavior Genetics Predicting Individual
Differences
Behavior geneticists study how heredity and
environment contribute to human differences.

• The topics in the text
• genes
• twin and adoption studies
• temperament and heredity
• molecular genetics
• heritability
• gene/environment interaction

Lets start by looking at GENES.
5
GENES The Building Blocks of Heredity and
Development
Genes are parts of DNA molecules, which are found
in chromosomes in the nuclei of cells.
DNA (Deoxyribonucleic Acid)
6
Chromosomes are made of DNA, which are made of
genes.

• Chromosome
• threadlike structure made largely of DNA molecules

DNA a spiraling, complex molecule containing
genes

7
DNA

• Watson and Crick (1953)
• Identified the molecules structure
• Double helix
• 4-letter alphabet code A,G,T,C 4 Nucleotides
• Mechanism of replication discovered
• DNA an amazing little replicator
• Nobel Prize (1962)
• "for their discoveries concerning the molecular
  structure of nucleic acids and its significance
  for information transfer in living material"

8
Chromosomes and Inheritance

• The human genome includes 46 chromosomes in 23
  sets matched sets each chromosome has the same
  gene locations.
• This includes the X and Y chromosomes, not a
  matched set in males, who are missing some genes
  on the Y.
• A biological parent donates half his/her set of
  chromosomes to his/her offspring.
• We received half a set of chromosomes from each
  biological parent.

9
The Human Genome20,000 to 25,000 Genes
The genome an organisms entire collection of
genes

• Human genomes are so nearly identical that we can
  speak of one universal human genome.
• Yet tiny genetic differences make a difference.
  If there is a
• .001 percent difference in genome, your DNA would
  not match the crime scene/you are not the babys
  father.
• 0.5 to 4 percent difference in genome, you may be
  a chimpanzee.
• 50 percent difference in genome, you may be a
  banana.

10
How Genes Work

• Genes are not blueprints they are molecules.
• These molecules have the ability to direct the
  assembly of proteins that build the body.
• This genetic protein assembly can be turned on
  and off by the environment, or by other genes.
• Any trait we see is a result of the complex
  interactions of many genes and countless other
  molecules.

11
Next step for behavior geneticistsControlling
Variables
Can we design an experiment to keep genes
constant and vary the environment and see what
happens?

• Or vary the genes in the same environment?

12
Fraternal and Identical Twins

• Twin and Adoption Studies
• To assess the impact of nature and nurture, how
  do we examine how genes make a difference within
  the same environment?
• study traits of siblings vs. identical twins
• see if the siblings vary more than twins

• Fraternal twins from separate eggs are not any
  more genetically alike than other siblings.

13
Identical vs. Fraternal Twins
Twin and Adoption Studies How do we find out how
the same genes express themselves in different
environments? We can study the traits of
identical twins as they grow up, or if they were
raised separately (e.g., the Minnesota Twin
Family Study).

• Studies of twins in adulthood show that identical
  twins are more alike than fraternal twins in
• personality traits such as extraversion
  (sociability) and neuroticism (emotional
  instability).
• behaviors/outcomes such as the rate of divorce.
• abilities such as overall Intelligence test
  scores.

14
Studies of Identical Twins Raised Apart

• Critiques of Twin Studies
• In the more recent years of the Minnesota Twin
  Family Study, twins have known about each other
  and may influence each other to be more similar.
• Coincidences happen some randomly chosen pairs
  of people will have similar traits, including
  even spouses, children, and dogs with identical
  names.
• Environments may be similar adoptive families
  tend to be more similar than randomly selected
  families in education, income, and values.

• Similarities found in identical twins despite
  being raised in different homes
• personality, styles of thinking and relating
• abilities/intelligence test scores
• attitudes
• interests, tastes
• specific fears
• brain waves, heart rate

BUT none of these factors explains, better than
the genetic explanation, why fraternal twins have
more differences than identical twins.
15
Searching for Parenting EffectsBiological vs.
Adoptive Relatives

• Studies have been performed with adopted children
  for whom the biological relatives are known.
• Findings Adopted children seem to be more
  similar to their genetic relatives than their
  environmental/nurture relatives.

Given the evidence of genetic impact on how a
person turns out,does parenting/nurture make
any difference? Does the home environment have
any impact?
16
Parenting Does Matter

• Despite the strong impact of genetics on
  personality, parenting has an influence on
• religious beliefs
• values
• manners
• attitudes
• politics
• habits

17
If parenting has an influence, why are siblings
so different?

• Siblings only share half their genes.
• Genetic differences become amplified as people
  react to them differently.
• Siblings are raised in slightly different
  families the youngest has more older siblings
  and has older (wiser? more tired?) parents.

18
Temperament is another difference not caused by
parenting.

• From infancy into adulthood, most people do not
  seem to change temperament (defined as a persons
  general level and style of emotional reactivity).
  
• According to some researchers, three general
  types of temperament appear in infancy
• easy
• difficult
• slow to warm up

19
Molecular Genetics

• Molecular genetics is the study of the molecular
  structure and function of genes.
• Molecular genetics might help us see exactly how
  specific genes have an influence on behavior.
• Genetic tests can reveal which people are at risk
  for many physical diseases, and may soon identify
  people at risk of mental health disorders.
• Ethical conundrum should people use genetic
  tests to select sperm, eggs, and even embryos?

20
Heritability

• Clarifying Heritability
• If five unrelated people had nearly identical
  upbringing, but differed in a trait such as
  shyness, then the heritability of this trait for
  them is close to 100 percent.
• Nurture may have influenced how shy they are, but
  because it influenced them all in the same way,
  any differences are almost certainly caused by
  genes.

• When you see a variation of some trait within a
  population, the heritability of that trait is the
  amount of variation in the population that is
  explained by genetic factors.
• This DOES NOT tell us the proportion that genes
  contribute to the trait for any one person.
• The heritability of a trait also does not tell us
  whether genetics explain differences between
  groups/populations.

21
Nature and nurture working togetherInteraction
of Genes and Environment

• Some traits, such as the overall design of our
  bodies, are set by genes.
• Other traits, such as physical and mental
  abilities, develop in response to experience.

How does the interaction of genes and environment
work?

• Genetic traits influence the social environment,
  which in turn affects behavior.

22
How does the interaction of genes and environment
work?
Example of self-regulation in animals shortened
daylight triggers animals to change fur color or
to hibernate

• Self-regulation genes turn each other on and off
  in response to environmental conditions
• Epigenetics the environment acts on the surface
  of genes to alter their activity

Example of self-regulation in humans obesity in
adults can turn off weight regulation genes in
offspring
23
The Human Approach to Nature and Nurture

• The trait of being adaptable is built into the
  human genome.
• Paradox our genes allow us not to be tied so
  much to our genes!
• We have minds which allow us to change our
  behavior in response to the environment to a
  greater degree than other species.
• We even shape our environments to suit our
  nature.
• Humans can adapt to a variety of climates, diets,
  lifestyles, and skills.

24
Evolutionary Psychology Understanding Human
Nature
Evolutionary psychology is the study of how
evolutionary principles help explain the origin
and function of the human mind, traits, and
behaviors.

• Some topics
• Natural selection and adaptation
• Evolutionary success may help explain
  similarities
• An evolutionary explanation of human sexuality

We have been talking so far about human
differences we may now seek insight in the ways
in which humans are alike.
25
Evolutionary Psychology Natural Selection How
it Works
26
Artificial Selection The Domesticated Silver Foxes

• Dmitri Balyaev and Lyudmila Trut spent 40 years
  selecting the most gentle, friendly, and tame
  foxes from a fox population, and having those
  reproduce.
• As a result, they were able to shape avoidant and
  aggressive creatures into social ones, just as
  wolves were once shaped into dogs.

27
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.

28
Evolutionary Psychologys 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?

29
A Possible Human Genetic Legacy Illogical
Moral Reasoning

• It might be logical to kill one innocent person
  if it would enable five other innocent people to
  live. Research shows that most people can imagine
  letting the one person die, but cannot picture
  killing the person themselves.

Why would it be instinctual not to kill unless we
are directly threatened?
30
Male and Female Differences Focusing on Mating
Preferences

• First issue quantity (of mating)
• Generally, men think more than women about sex,
  and men are more likely to think that casual sex
  is acceptable.
• Why might natural selection have resulted in
  greater male promiscuity?

An evolutionary psychologists answer
For women, a trait of promiscuity would not
greatly increase the number of babies, and it
would have greater survival costs (pregnancy,
once a life-threatening condition).
Men who had the trait of promiscuity were more
likely to have their genes continue, and even
spread, in the next generation. And there is
little cost to spreading extra genes.
31
Possible Evolutionary Strategies in Seeking
Partners
Q How would evolutionary psychology explain why
males and females have different preferences for
sexual partners?

• Men seek women with a fuller figure
• to make sure they are not too young or too old to
  have children?
• Women seek males with loyal behavior and
  physical/social power and resources
• in order to ensure the survival of the mothers
  offspring?

32
Critiquing the Evolutionary Perspective on Gender
Differences in Sexuality
Are males and female really so different in their
mating choices?
Differences are less in cultures that move to
gender equality.
Isnt much of gender behavior a function of
culture?
Yes, as well see later in this lesson.
How do you explain homosexuality?
Guesses such as population control or misplaced
instincts are unproven and seem forced.
Does evolutionary psychology really tell us
anything useful?
See next slide
33
Critiquing Evolutionary Psychology
Youre just taking current reality and
constructing a way you could have predicted it.
This is hindsight reasoning and unscientific.
Youre attributing too much to genes rather than
the human ability to make choices about social
behavior.
Response yes, but there are predictions made
about future behavior using this reasoning.
Response yes, but our evolutionary past does not
prevent our ability to act differently is does
not equal ought.
34
Nature/NurtureFrom Genes to the Role of
Environment

• How environment/experience affects brain
  development
• Forces guiding the course of development
• parents
• peers
• culture

Our starting picture
35
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.

36
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.

37
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.

38
Is parenting a powerful environmental influence
on development?

• Generally, environmental influences, including
  parenting, account for about 10 percent of
  temperament, although a much higher percentage
  for other features such as values.
• 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
39
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 childs peers, such as by selecting a
  school or neighborhood. However, ultimately, most
  children self-select their peers.

40
Parents vs. PeersBattling over non-genetic
influence

• Peers have more influence on

• Parents have more influence on

• Education and career path
• Cooperation
• Self-discipline
• Responsibility
• Charitableness
• Religion
• Style of interaction with authority figures

• 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

41
Culture Influences on Development
The nature of culture
Variation across cultures
Examples of cultural variation over time

• Culture refers to the patterns of ideas,
  attitudes, values, lifestyle habits, and
  traditions shared by a group of people and passed
  on to future generations.
• Culture is not just an influence on our nature,
  but it is also part of our nature. Humans form
  not only relationships, but culture.

• Each culture has norms--standards for acceptable,
  expected behavior.
• Example Eww, you wear your shoes from outdoors
  right into the house?
• Culture shock feeling lost about what behaviors
  are appropriate

• Cultural variation can occur even within one
  culture
• language changes in vocabulary and pronunciation
• the pace of life quickens
• gender equality increases.
• people sleep less, socialize in person less,
  stare at screens more
• people marry more for love, but then expect more
  romance
• These cultural changes occur too fast to be
  rooted in genetic change.

42
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

43
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.

44
Culture and GenesA 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.
45
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.

46
Gender Development

• Gender refers to the physical, social, and
  behavioral characteristics that are culturally
  associated with male and female roles and
  identity.
• Some of these traits may be genetic differences
  other role differences may be nurtured by culture.

47
Group differences?

• In this example related to self-esteem, the
  difference between groups is small compared to
  differences within each gender.

48
Differences Between Genders
Biological women enter puberty earlier, live
longer, and have more fat and less muscle

• 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

• 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

49
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.

50
Gender and Social Connection Play

• When women play, the focus tends to be on
  connection and conversation.
• Female play is more social.
• Girls tend to invite feedback.

• 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.

Are these differences due to nature or nurture?
51
Gender and Social Communication
However, men and women speak about the same
number of words per day. What fills in the extra
time on those longer phone calls?

• Women communicate more than men
• more time with friends
• more text messages
• longer phone calls

Maybe. listening?
52
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.
• In general, women change roommates more often.
• Women tend to have stronger ties to friends and
  family.
• Women are often more involved with religion.

53
The Biology of Gender

• Brain Differences
• During the fourth and fifth month of pregnancy,
  sex hormones bathe the fetal brain.
• In adulthood, women have thicker areas in a part
  of the frontal lobes that help with verbal
  fluency.
• There are also differences in the amygdala,
  hippocampus, and ratio of cell bodies to axons.

• What biologically makes us male or female?
• It begins with whether our 23rd pair of
  chromosomes looks like XX (female) or Xy (male).
• Testes develop, and at seven weeks, the testes
  produce a flood of testosterone.
• Hormones then guide the development of external
  sex organs.

54
Lessons about Gender Unusual Biological Cases

• Breaking Free of Gender
• Transgendered people have a sense of sexual
  identity that is different from their birth sex.
• Transsexual people act on this sense of
  difference by living as a member of the opposite
  sex, often with hormonal and surgical
  interventions that support this gender
  reassignment.

• In cases in which prenatal testosterone levels
  were high in females, there is an increase in
  tomboyish behavior, possibly caused by other
  peoples response to more masculine features.
  However, there is not a general pattern of gender
  identity change.
• In cases where males had underformed or absent
  genitalia, attempts to raise them as females
  generally did not work out well.

55
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 ones 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 its mans job to get the high paying
employment,
If its womens 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?

56
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.

57
Culture Influence on Gender Role DevelopmentOr
is it instinct?

• Social learning theory we learn gender role
  behavior by imitation, and by rewards and
  punishments that shape our behavior
• Gender schemas the cognitive frameworks for
  developing concepts of male and female these
  frameworks guide our observations
• Gender typing the instinct which drives some
  children to fit into traditional gender roles

58
Influences on Who Youve Become
59
Beyond Biopsychosocial Influences CHOICE

• Is our behavior and identity rigidly determined
  by our combination of nature/genes and
  nurture/experience?
• Even if free will is an illusion, it would seem
  that 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.

60
Epilogue Evolution

• Possible areas of consensus, with or without
  evolution
• The human mind and body seems almost designed,
  by evolution or other forces, to have certain
  traits and abilities.
• Nurture may shape us, but we seem to start out
  with some sort of human nature.

• Evolution is a scientific theory (NOT a guess,
  and not a hypothesis, but something more) a
  coherent set of principles that fits very well
  with the accumulated evidence.
• Parts of the evolutionary story may conflict with
  other stories of origins and change over time.
• Is there room for overlap and agreement?