how do families, friends and culture affect the way we live?
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CHAPTER 3NATURE VS. NURTURE
How do families, friends and culture affect the way we live?
Behavior Genetics
- Study the relative effects of genes and environment on behavior
- The nature vs. nurture debate
Genetics in Brief
Genes – biochemical units of heredity that make up a chromosome
Chromosome – Threadlike structures made of DNA molecules that contain genes (46 total, 23 from each parent)
DNA (deoxyribonucleic acid) – complex molecule that contains genetic information that makes up chromosomes
Cell -> Nucleus -> Chromosomes -> DNA -> Genes
Human Genome Genes made up of
nucleotides (A,T,C, or G) Genome – complete
instructions for making an organism consisting of all genetic material in its chromosomes
Humans have about 30,000 different genes
Does anyone know the animal humans are most genetically related to?
Predisposition
Genes are responsible for predisposing our appearance and behavior, not concretely determining either.
Predisposition – a situation that allows something else to occur but doesn’t necessarily cause it to occur; “Her genetic makeup left her with a predisposition to develop Alzheimer's.”
Mutations – random error in gene replication that lead to a change in genetic code
Charles Darwin and Evolution
Natural selection – the idea that , among the inherited trait variations, those contributing to survival will most likely be passed on to future generations
Adaptation – species changing genetically to better survive in their environment
Class Discussion
What correlation does economic/social status of a country have with reproduction rates worldwide if any?
Why do people in poorer countries have more babies? And should they have more babies?
Is this natural selection at work here? Why or why not?
Twin Studies: Score one for Nature
Identical twins – twins that develop from a single fertilized egg and then split in half; are genetically identical
Fraternal twins – twins that develop from separate eggs; no more related genetically than normal siblings
Twin studies have discovered that identical twins are strikingly similar is intelligence, attitude and even brain waves!
Fig. 12-14, p. 493
Although they were reared apart from 4 weeks after their birth, Jim Lewis (left) and Jim Springer (right) exhibit remarkable correspondence in
personality. Some of the similarities in their lives—such as the benches built around trees in their yards—seem uncanny.
Adoption Studies: Score another for nature!
Studies of adopted children show that they exhibit similar personality traits of their biological parents
However, adopted children tend to be smarter, more productive and more successful than their biological parents
Nurture is back in the game!
Fig. 9-13, p. 353
Environment Matters Are parents to
blame for success/failure of children? Studies say “not really”.
Siblings raised together tend to be as different personality-wise as two random people on the street.
Early Learning and Brain Development
For our brains to reach their developmental potential, early experience is CRITICAL.
Children raised in abusive homes tend to be less intelligent that children raised in loving environments.
Score one for nurture!
Peer and Parent Influence
Peers hold a heavy influence on the behaviors of individuals (i.e. smoking, drinking, promiscuity )
Bandwagon phenomenon “Fitting In” Parents influence behaviors of children by
supplying them the environment from which they have to work within (i.e. parents “choose” which neighborhood to live in)
Peer InfluenceChildren, like adults, attempt to fit into a
group by conforming. Peers are influential in such areas as learning to cooperate
with others, gaining popularity, and developing interactions.
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Parenting
Parenting does have an effect on biologically related and unrelated
children.Parenting Influences
Children’s
Attitudes, Values
Manners, Beliefs
Faith, Politics
Cultural Influence
Culture – shared attitudes and beliefs of a group passed on from one generation to the next.
Norms – understood rules for accepted and expected behavior; prescribe “proper” behavior
Individualism – giving priority to one’s goal over the goals of the group
Collectivism – giving priority to the group’s goal over the goal of the individual
Gene-Environment Interaction
Genes can influence traits which affect responses, and environment can affect
gene activity.
A genetic predisposition that makes a child restless and hyperactive evokes an
angry response from his parents. A stressful environment can trigger genes
to manufacture neurotransmitters leading to depression.
Some Traits Show More Heritability Than Others
Height Temperament
refers to a person’s stable emotional reactivity and intensity. Identical twins express similar temperaments, suggesting heredity predisposes temperament.
As environments become more similar, heredity as a source of difference become more important (since difference due to environment has decreased).
Gene-Environment Interaction
Genes and environment affect our traits individually, but more important are their
interactive effects.
People respond differently toRowan Atkinson (Mr. Bean) than Orlando bloom.
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Culture and Child-Rearing
Westernized CulturesAsian-African
CulturesResponsible for your
selfResponsible to group
Follow your conscience Priority to obedience
Discover your gifts Be true to family-self
Be true to yourself Be loyal to your group
Be independent Be interdependent
Developmental Similarities Across Groups
Despite diverse cultural backgrounds, humans are more similar than different in
many ways. We share the same genetic profile, life cycle, capacity for language,
and biological needs.
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Variation Over Time
Culture changes over time. The rate of this change may be extremely rapid. In many Western
countries, culture has rapidly changed over the last 40 years. This change cannot be attributed
to changes in the human gene pool because genes evolve very slowly.
Gender Development
Based on genetic makeup, males and females are alike, since the majority of
our inherited genes (45 chromosomes are unisex) are similar. Gender is determined
by only one chromosome.
Males and females differ biologically in body fat, muscle, height, onset of puberty,
and life expectancy.
Biology of Sex
Biological sex is determined by the twenty-third pair of chromosomes. If the pair is XX, a female is produced. If the pair is XY, a male
child is produced.
Sexual Differentiation
In the mother’s womb, the male fetus is exposed to testosterone (because of the
Y chromosome) which leads to the development of male genitalia.
If low levels of testosterone are released in the uterus, the result is female.
Physical Differences
The average…than the average man. woman begins puberty 2 years earlier woman lives 5 years longer woman has 70% more body fat and tend to
carry it in different areas of the body woman has 40% less muscle woman is 5” shorter woman is far less likely to be colorblind woman is doubly vulnerable to depression and
anxiety woman’s risk of developing an eating disorder is
10x greater
Psychological Differences
The average man is 5x more likely to commit suicide or suffer alcohol dependence than the average woman.
The average man is more likely to develop autism, ADHD or personality disorder than the average woman.
Gender Differences in Aggression
Men express themselves and behave in more aggressive ways than do women. This aggression gender gap appears in
many cultures and at various ages.
In males, the nature of this aggression is physical.
In the US, the male-to-female arrest ratio for murder is 10:1.
Gender and Social Power
In most societies, men are socially dominant and are perceived as such.
In 2005, men accounted for 84% of the governing parliaments.
Gender Differences and Connectedness
Young and old, women form more connections (friendships) with people than do men. Girls
tend to play in smaller groups with more intimate relationships. Boys emphasize
competition, freedom and self-reliance while playing in larger groups.
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Gender Roles
Our culture shapes our gender roles — expectations of how men and women are
supposed to behave.
Gender Identity — means how a person views himself or herself in terms of
gender.
Gender Roles: Theories
1. Social Learning Theory proposes that we learn gender behavior like any other behavior—reinforcement, punishment, and observation.
2. Gender Schema Theory suggests that we learn a cultural “recipe” of how to be a male or a female, which influences our gender- based perceptions and behaviors.
Reflections on Nature and Nurture
Evolutionary Psychology: Understanding Human Nature
Evolutionary psychology studies why we as humans are alike. In particular, it studies the
evolution of behavior and mind using principles of natural selection.
The following traits would benefit humans in that they would provide an advantage for survival and
reproduction: The mental capacities for acquiring language. The ability to infer emotion in others and to
cooperate with others. The preference for healthier, more fertile
mates.
Evolutionary Success Helps Explain Difference
No more than 5% of the genetic differences among humans arise from population group differences. Therefore, 95% of genetic variation exists within populations.
The typical genetic difference between two Icelandic villagers or between two Kenyans is much greater than the average difference between to the two groups.
Human Traits
A number of human traits have been identified as a result of pressures
afforded by natural selection.
Why do infants fear strangers when they become mobile?
Why do people fear spiders and snakes and not electricity and guns?
How are men and women alike? How and why do men’s and women’s sexuality differ?
Human Sexuality
Males and females, to a large extent, behave and think similarly. Differences in
sexes arise in regards to reproductive behaviors. In the U.S.:
Gender Differences in Sexuality
Question (summarized) MaleFemal
e
Casual sex 58% 34%
Sex for affection 25% 48%
Think about sex everyday 54% 19%
Natural Selection & Mating Preferences
Natural selection has caused males to send their genes into the future by mating with multiple females since males have lower
costs involved.
However, females select one mature and caring male because of the higher costs involved with pregnancy and nursing.
Mating Preferences
Males look for youthful appearing females in order to pass their genes into the future.
Females, on the other hand, look for maturity, dominance, affluence and
boldness in males.
Data based on 37 cultures.
Mating Preferences
Men are typically more attracted to a woman whose waists are roughly a third narrower than their hips – a sign of future fertility.
Men are attracted to women who are at the age of peak fertility (which has shifted over time).
Women are more attracted to men who seem more mature, dominant, bold and affluent.
Critiquing the Evolutionary Perspective
Evolutionary psychologists take a behavior and work backward to explain it in terms of natural
selection.
Evolutionary psychology proposes genetic determinism and undercuts morality in
establishing society.
Where genders are unequal, gender preferences are wide, but when they are closely equal,
preferences narrow down.
Evolutionary Psychologists Reply
Evolutionary psychologists argue that we need to test behaviors that expound evolutionary
principles.
Evolutionary psychologists remind us how we have adapted, but do not dictate how we ought
to be.
Males and females are more alike than different, and if we study these differences we can
establish their causes.
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