Nature, Nurture, and Human Diversity Differences and similarities within the human family

Similarities Differences

Genes: Same set of chromosomes

Genes: Genetic anomalies may make us different

Biology: Organs and body functions same

Biology: May change during development

Brain: Same brain architectureBrain: Asymmetry of brain

across genders

Behaviors: Speak languageBehavior: Speak different

languages

Genes are parts of DNA molecules, which are found in chromosomes in the nuclei of cells.

DNA (Deoxyribonucleic Acid)

GENES:The Building Blocks of Heredity and Development

Genes are parts of DNA molecules, which are found in chromosomes in the nuclei of cells.

GENES:The Building Blocks of Heredity and Development

Chromosomes are made of DNA, which are made of genes.

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Chromosome: threadlike structure made largely of DNA molecules

DNA: a spiraling, complex molecule containing

genes

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.

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.

Dominant and Recessive

Genotype—underlying genetic makeup Phenotype—traits that are expressed Dominant genes—will always be

expressed if present Recessive genes—will not be expressed

unless they are in a pair

Sex Linked Traits Traits linked to the X or Y (sex)

chromosomes Usually recessive and carried on the X

chromosome Appear more frequently in one sex than

another Color blindness, baldness, hemophilia,

Fragile X

Twin and Adoption StudiesTo 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 and Identical Twins

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

Identical twin: Same sex only

Fraternal twin: Same or opposite sex

Twin and Adoption StudiesHow 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).

Identical vs. Fraternal TwinsStudies 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.

Critiques of Twin Studies1.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.2.Coincidences happen; some randomly chosen pairs of people will have similar traits.3.Environments may be similar; adoptive families tend to be more similar than randomly selected families in education, income, and values.

Studies of Identical Twins Raised ApartSimilarities found in identical twins despite being raised in different homes:personality, styles of thinking and relatingabilities/intelligence test scoresattitudesinterests, tastesspecific fearsbrain waves, heart rate

BUT none of these factors explains, better than the genetic explanation, why fraternal twins have more differences than identical twins.

Searching for Parenting Effects:Biological vs. Adoptive RelativesStudies 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?

Despite the strong impact of genetics on personality, parenting has an influence on:

religious beliefs values manners attitudes politics habits

Parenting Does Matter

Gene-Environment Interaction: genes turn each other on and off in response to environmental conditions

Epigenetics: The study of how this happens: The environment acts on the surface of genes to alter their activity

How does the interaction of genes and environment work?

Example in animals: shortened daylight triggers animals to change fur color or to hibernate

Example in humans: obesity in adults can turn off weight regulation genes in offspring

Behavior Genetics Temperament

a person’s characteristic emotional reactivity and intensity

Identical twins express similar temperaments, suggesting heredity predisposes temperament

Behavior Genetics Heritability

the proportion of variation among individuals that we can attribute to genes

Heritability refers to the extent to which the differences among people are attributable to genes.

Group Differences Group differences and environmental impact

Variation within group

Variation within group

Difference within group

Poor soil Fertile soil

Seeds

Group Differences

If genetic influences help explain individual diversity in traits, can the same be said about

group differences?

Not necessarily. Individual differences in weight and height are heritable and yet nutritional

influences have made westerners heavier and taller than their ancestors were a century ago.

Prenatal Environment

Identical twins who share the same placenta (b) are more alike than those who do not (a), suggesting

prenatal influences on psychological traits.

Experience and Brain Development

Early postnatal experiences affect brain development. Rosenzweig et al. (1984) showed

that rats raised in enriched environments developed thicker cortices than those in

impoverished environment.

Brain Development and Adulthood

Brain development does not stop when we reach adulthood. Throughout our life, brain

tissue continues to grow and change.

A well-learned finger-tapping task leads tomore motor cortical neurons (right) than baseline.

Variation Across Culture

Cultures differ. Each culture develops norms – rules for accepted and expected behavior. Men

holding hands in Saudi Arabia is the norm (closer personal space), but not in American culture.

Jason Reed/ R

euters/Corbis

Environmental Influence Personal Space

the buffer zone we like to maintain around our bodies

Memes self-replicating ideas, fashions, and

innovations passed from person to person

Variation Over Time

Cultures change over time. The rate of this change may be extremely fast. In many

Western countries, culture has rapidly changed over the past 40 years or so.

This change cannot be attributed to changes in the human gene pool because genes evolve

very slowly.

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Some topics: Natural selection and

adaptation Evolutionary success may help

explain similarities An evolutionary explanation

of human sexuality

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.

We have been talking so far about human differences; we may now seek insight in the ways in which humans are alike.

Evolutionary Psychology: Natural Selection: How it Works

Evolution: Theory 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?

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.

Gender DevelopmentGender 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.

Gender differences and similarities

Similarities: 45 out of 46 genes are unisexSame body and brain structures and functionsSimilar levels of Intelligence, knowledge, happiness

Compared to men, women (as a group, on average): •Start puberty 2 years sooner•Live 5 years longer•Have 70% more fat•Have 40% less muscle•Are 5 inches shorter•Express more emotion•Are more vulnerable to anxiety, depression •Are less prone to autism, alcohol dependence, ADHD, antisocial personality, and suicide

Average/Group differences do not predict individual comparisons

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

This means: many women rate higher than the average man, in self esteem and other measures.

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.

And yet violent acts by women do occur, including acts of terrorism.

Bombing in Russia by female suicide bombers

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 friendsmore text messageslonger 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

explore relationships. Women speak about

people and feelings.

Men state their opinions and solutions .

Men speak about things and 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.

In general, women change roommates more often.

Women tend to have stronger ties to friends and family.

Women are often more involved with religion.

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.

The Biology of Gender

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.

Brain DifferencesDuring 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.

Gender Roles: The Influence of Culture

Does culture define which behaviors fill a gender role? Or do the roles affect 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

Gender roles and culture: Expectations may vary

Gender roles have simplified, yet constrained, choices for men and women.

In the past century, women have been gaining more options for participation in workplaces and politics.

In North American societies, men have

been providers, women were caretakers

In some societies, men and women share more

in child rearing and accumulating resources

Culture Influence on Gender Role Development

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

Gender Schema Theory

Gender-role development is influenced by the formation of schemas, or mental representations, of masculinity and femininity

An example of how a child forms a schema associated with gender. A girl is offered a choice of 4 toys to play with.

I am a girl

Toy car

Doll

Orange

Artichoke

Approach object

Who for?

Is it relevant to me?

Avoid/Forget

Assign to category and remember/Approach

Not for me

For me

Boys

Girls

The Nature and Nurture of Gender Two theories of gender typing

Variations in Sexual Identity

Breaking free of gender rolesTransgendered people have a sense of sexual identity (sense of being male or female) or gender expression (behaviors and appearance that express gender identity) that is different from what is culturally typical for the biological sex/gender they were born with.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.

Hormones and Sexual Behavior Hormones such as estrogens

(female sex hormones) and also in testosterone (male sex hormones) guide the physical development of sex characteristics and behaviors.

During ovulation, women show a rise in both sex hormones.

As this happens, sexual desire rises in women and also in the men around them (whose testosterone level rises).

Low levels of testosterone can reduce sexual motivation.

Sex hormone levels fall with age (menopause), drugs, or surgery.

Males and females are very close in overall intellectual abilities.

Intelligence

Spatial SkillsSkills involving the ability to imagine how objects would look when moved about in space. Males generally do better though social role, social class, ethnic background, and the type of test given also play roles.

Social Factors

Self-Confidence In adolescence, females’ confidence often declines

(concerned with how boys will react to them?).

The loss of confidence is highest in whites and Hispanics and lowest in African Americans.

Overall, studies have not found major differences in self-confidence levels between males and females.

Friendships Boys’ groups usually have a leader, girls

have more equal status in groups.

Boys usually issue orders and demands while girls make more suggestions.

Adult females tend to have a best friend of the same sex while males do not.

Adult females have a few close friends while males have a larger number of male acquaintances.

Females initiate most breakups.

Selecting a MateOverall, the top eight characteristics for potential mate selection are:

1. Social Status

2. Economic Status

3. Physical Attractiveness

4. Personality

5. Intelligence

6. Ambition

7. Character

8. Sense of Humor

Gender Differences in Sexuality: An Evolutionary Perspective

• 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 psychologist’s 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.

Natural Selection and Mating Preferences

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 mother’s offspring?

Q: How would evolutionary psychology explain why males and females have different preferences for sexual partners?

Gender Role Behavior

Gender role behaviors reflect what society says are appropriate actions for males and females.

Through identification with a parent of the same sex, people learn how to behave appropriately.

Which jobs are appropriate for males? for females?

Fathers who are very warm toward daughters tend to produce mild tomboyishness in girls.

Boys whose fathers were absent during preschool years tend to be less aggressive and not as active in sports.

People who are considered mentally healthy tend not to have excessive masculine or feminine qualities.

Children tend to identify with the dominant parent in the household, even across sex lines.

Gender studies have shown

Fathers are more determined that appropriate activities are given to young male children.

People handle babies differently depending on whether they are identified as male or female.

People will assign different characteristics to babies when they are identified as male or female.

Mixing Gender Roles

Rigid extremes for gender roles for males and females restrict the full range of human behaviors and emotions.

Androgynous people are high in male and female characteristics.

Androgynous behavior can lead to more flexibility and willingness to share characteristics of members of the opposite sex.

Gender-Busting Communication Hints (for Males)

1. Do you frequently interrupt females while they are speaking? Try to break the habit.

2. Avoid answering questions with “Nope”and “Yep.” Try to explain more and give some details why you did something.

3. Try to open up on personal issues.

4. Ask for help if you need it.

Can you tell me how to get to . . .?

Can you tell me how to get to . . .?

1. Look people directly in the eye.

2. If men interrupt conversations, assertively direct the conversation back.

3. Do not over-apologize for your behaviors.

4. Talk more often about current events, less about people.

Gender-Busting Communication Hints (for Females)

Reflections on Nature and Nurture