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

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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.