Nature, Nurture, and Human Diversity - Study Notes

Chapter Overview

• Behavior Genetics: Predicting Individual Differences
• Evolutionary Psychology: Explaining Human Nature and Nurture
• Culture and Gender Diversity: Understanding Nature and Nurture

Genes: Our Codes for Life

• Genes: Biochemical units of heredity that make up chromosomes, the threadlike coils of DNA.
  • When genes are expressed, they provide the code for creating proteins, which form the body’s building blocks.

Chromosomes and Inheritance

• The human genome is the shared genetic profile that distinguishes humans from other species.
• Consists of all the genetic material in an organism’s chromosomes.
  • The human genome includes 46 chromosomes in 23 matched sets; each chromosome has the same gene locations.
  • The X and Y chromosomes are not a matched set in males, who are missing some genes on the Y chromosome.
• Each biological parent donates half of his or her set of chromosomes to his or her offspring.
• Each person receives half a set of chromosomes from each biological parent, which is the mechanism of evolution and adaptation.

Terms to Learn (part 1)

• Behavior genetics: The study of the relative power and limits of genetic and environmental influences on behavior.
• Heredity: The genetic transfer of characteristics from parents to offspring.
• DNA (deoxyribonucleic acid): Complex molecule containing the genetic information that makes up the chromosomes.
• Chromosomes: Threadlike structures made of DNA molecules that contain the genes.

Terms to Learn (part 2)

• Genome: The complete instructions for making an organism, consisting of all the genetic material in that organism’s chromosomes.

Identical Versus Fraternal Twins

• Identical twins: Develop from a single fertilized egg.
• Fraternal twins: Develop from two different eggs.
• Identical twins do not always have the same number of copies of genes and may share different placentas.

Understanding the Effects and Interactions of Nature and Nurture

• Studies comparing:
  • Identical twins versus fraternal twins
  • Separated twins
  • Biological versus adoptive families
• Allow researchers to differentiate the influences of heredity and environment:
  • Separated identical twins maintain the same genes while testing the effects of different home environments.
  • Adoptive families maintain the same home environment while studying effects of genetic differences.

Behavior Genetics: Twin and Adoption Studies (part 1)

• Studies show that identical twins are more alike than fraternal twins in:
  • Personality traits such as extraversion (sociability) and neuroticism (emotional instability).
  • Behaviors/outcomes like the rate of divorce.
  • Abilities reflected in overall intelligence test scores.

Behavior Genetics: Twin and Adoption Studies (part 2)

• Similarities in identical twins, even when raised in different homes include:
  • Personality
  • Styles of thinking and relating
  • Abilities/intelligence test scores
  • Attitudes
  • Interests, tastes
  • Specific fears
  • Brain waves, heart rate

Behavior Genetics: Biological Versus Adoptive Relatives

• Studies conducted with adopted children for whom the biological relatives are known indicate that:
  • Adopted children seem more similar to their genetic relatives than to their environmental/nurture relatives.
• Questions arise regarding the impact of parenting/nurture on outcomes.
• Queries about whether the home environment influences children significantly.

Why Are Siblings Different?

• Siblings share only half their genes; genetic differences can be amplified by varying reactions to them.
• The environment changes with each addition to a family:
  • Siblings are raised in slightly different families; the youngest child has more older siblings and older parents.

Temperament and Heredity (part 1)

• Temperament: A person’s characteristic emotional reactivity and intensity; evident from the first weeks of life and generally persists into adulthood.
  • Genetic effects exhibit as physiological differences:
  • Anxious, inhibited infants exhibit elevated/variable heart rates and a reactive nervous system, becoming more physiologically aroused in unfamiliar situations.

Temperament and Heredity (part 2)

• Research suggests that temperament differences usually persist throughout life:
  • Emotionally reactive infants remain emotionally reactive at nine months old.
  • Emotionally intense preschoolers are likely to become relatively intense young adults.
  • Identical twins, more than fraternal twins, often have similar temperaments.

Heritability

• Heritability: The proportion of difference among individuals that can be attributed to genetics.
  • Varies depending on the populations and environments studied.
  • Represents how much variability in a population is explained by genetic factors.
  • Does not reveal the contribution of specific genes to a trait for any single individual.

Gene-Environment Interaction

• Interaction: The interplay that occurs when one factor (like heredity) depends on the effect of another factor (such as the environment).
• The hallmark of our species is adaptability.

Molecular Behavior Genetics

• Molecular genetics studies the molecular structure and function of genes and searches for genes that combine to reveal complex traits such as body weight, sexual orientation, and impulsivity.
• Epigenetics: Study of environmental influences on gene expression that occur without a change to DNA.
  • Genes can be either expressed or inactive due to epigenetic marks created by our experiences, where environmental factors can trigger or block genetic expression.

Epigenetics Influences Gene Expression

• Life experiences from the womb lay down epigenetic marks—organic methyl molecules—that can affect gene expression.
  • This provides a mechanism for how childhood trauma, poverty, or malnutrition may have lasting effects throughout life.

Evolutionary Psychology: Natural Selection and Adaptation

• Evolutionary psychology: Study of behavior and mind evolution using natural selection principles.
  • Distinction arises from mutations, or new gene combinations at conception.
  • Focuses on commonalities as humans.
• Natural selection: Principle stating that inherited traits that improve an organism's chance of survival and reproduction are most likely to be passed on to future generations.

Natural Selection Mechanism

• A species’ genome contains diverse versions of genes influencing traits. Varied offspring compete for survival, and certain traits may hinder or help survival.
  • Successful individuals pass on their traits, altering population characteristics over time.

Example: 40-year Fox Study

• The Belyaev study aimed to transform wild foxes into friendly ones by:
  • Using 30 male and 100 female foxes.
  • Measured tameness via responses to feeding, handling, and petting.
  • Breeding tamer foxes over 30 generations resulted in a new breed that was “docile, eager to please, and unmistakably domesticated.”

Evolutionary Psychology: How Natural Selection Works (part 2)

• Natural selection grants humans a significant capacity to learn and adapt based on their environment.
• Both genes and experience contribute to wiring the brain—one sets the stage while the other stimulates reactions. Adaptive flexibility is critical for survival and reproduction.

Our Genetic Legacy

• Humans share a common genome with a “universal moral grammar” transcending cultural differences.
• Prehistoric genetic legacies may clash with contemporary lifestyles, leading to various issues.

Interrelation of Nature and Nurture

• It is incorrect to consider it a competition of nature versus nurture; rather, it is Nature via Nurture.

Male-Female Differences in Sexuality (part 1)

• Men think more about sex than women.
• Men are more likely to accept casual sex.
• Natural selection may explain increased male promiscuity.

Male-Female Differences in Sexuality (part 2)

• Evolutionary psychology posits that men with promiscuous traits had a greater chance of passing on their genes, with fewer repercussions compared to women, whose promiscuity can involve greater survival risks due to pregnancy.

Male-Female Differences in Mating Preferences

• Men are attracted to women showing signs of fertility.
• Women prefer men displaying loyalty and resourcefulness.
• Natural selection informs these preferences, as male choices optimize offspring production and female choices ensure offspring survival.

Critiquing the Evolutionary Perspective

• While many psychologists recognize that natural selection shapes survival and reproduction, critics highlight that:
  • Immediate explanations often stem from social learning rather than distant ancestors’ decisions.
  • Social implications of these evolutionary explanations can be contentious.
  • Some human traits and behaviors are difficult to attribute solely to natural selection.

Experience and Brain Development (part 1)

• Nature and nurture interact to influence neural connections.
• Natural brain development leads to an abundance of neural connections.
• Understood connections become more efficient through a pruning process.

Experience and Brain Development (part 2)

• Lack of visual stimulation can lead to brain cells designated for vision to die off or get redirected.
  • Use it or lose it principle applies; however, brain development continues beyond childhood due to plasticity, allowing neural reorganization based on new experiences.

A Trained Brain

• Training on a finger-tapping task activates more motor cortex neurons than previously noted, showcasing changes following practice and learning.

Enriched Environment Impact

• Rats in enriched environments showed denser cortex development, with a brain weight increase of 7-10%, positively affecting neurological development in both animals and humans.

Cultural Influences

• Some behaviors evolve faster than genetic changes; culture exerts influence via:
  • Definition of Culture: The shared patterns of ideas, attitudes, values, lifestyle habits, and traditions passed down within groups.
• Culture is part of human nature, shaping relationships and identities.

Examples of Cultural Variation Over Time

• Learned behaviors can evolve separately from genetic predisposition.
  • Language, pace of life, gender equality, and interpersonal relationships have evolved significantly over time.

Cultural Influences on Development

• Individualism vs. Collectivism:
  • Individualist cultures promote independence and self-reliance, while collectivist cultures emphasize interdependence and support within groups.
• Social dynamics may differ significantly between cultures, affecting child-raising styles.

Value Contrasts Between Individualism and Collectivism

Culture and Child Raising (part 1)

• Parents everywhere care for their children, but their methods vary influenced by culture.
  • No single effective child-raising method; various practices can help children thrive.

Culture and Child Raising (part 2)

• Individualist cultures teach self-reliance, whereas collectivist cultures encourage social compliance.
• Emotional and physical proximity in raising children differs notably among cultures.

Blame or Credit? (part 1)

• Parental Influence: Parenting has often been blamed for negative child behaviors, with shared environmental influences accounting for less than 10% of personality differences.

Blame or Credit? (part 2)

• Peer Influence: Peer interactions can teach social skills and norms; they may be complementary to parental influences rather than oppositional.

Peer Influence

• As children mature, they focus more on peers for social norms. Influences of peers can shape eating habits, accent, and lifestyles.

Parents Versus Peers

• Parental Influence: Education, career, cooperation, self-discipline, responsibility, charitableness, religion, and interaction with authority figures.
• Peer Influence: Social skills, popularity, choices in entertainment and clothing.

Cultural Variation in Parenting

• Parenting practices vary by community size and social dynamics; urban and rural parenting methods diverge significantly.

Gender Development

• Sex: Biologically influenced characteristics defining boys and girls.
• Gender: The social, physical, and behavioral attributes culturally associated with maleness and femaleness.
  • Intersex individuals possess both male and female biological characteristics at birth.

The Nurture of Gender: Our Culture and Experiences (part 1)

• Gender role: Expected behaviors for males or females, which can change over time and situational contexts.
• Gender identity: A personal sense of being male or female.

The Nature of Gender

• Biological sex influences gender but does not dictate it.
  • Genetic and physiological differences include:
  • Males and females have different sex chromosomes; hormonal differences manifest in development.

Terms to Learn (part 4)

• X chromosome: Sex chromosome found in both sexes.
• Y chromosome: Sex chromosome present only in males.
• Testosterone: An androgen stimulating male sexual organ growth and male traits development during puberty.
• Estrogens: Hormones contributing to female characteristics, produced in greater quantities by females.

Adolescent Sexual Development: Puberty

• Puberty marks the onset of sexual maturity in both boys and girls, with rapid physical changes driven by hormonal surges.

Terms to Learn (part 5)

• Primary sex characteristics: Body structures (ovaries, testes) facilitating sexual reproduction.
• Secondary sex characteristics: Non-reproductive traits such as breast development in females and voice changes in males.
• Spermarche: The first ejaculation in boys.
• Menarche: The first menstrual period in girls.

The Nature of Gender: Our Biological Sex (part 4)

• Discusses variations in sexual development and related medical practices such as sex reassignment surgery.

The Nurture of Gender: Our Culture and Experiences (part 3)

• Schemas: Frameworks developed early in life that help children conceptualize the world based on gender.
• Gender expression can manifest through interests, language, and clothing choices.

The Nurture of Gender: Our Culture and Experiences (part 4)

• Androgyny: Displaying both masculine and feminine traits.
• Transgender: An overarching term for individuals whose gender identity or expression differs from their assigned sex at birth.

Reflections on Nature, Nurture, and Their Interaction

• Nature and nurture coexist within an open system; the biopsychosocial approach integrates all factors influencing individual development:
  • Biological factors: Evolution, genes, hormones, brains.
  • Psychological factors: Experiences, beliefs, feelings, expectations.
  • Social-cultural factors: Parental influences, peer interactions, cultural values, gender norms.