CHAPTER 4

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NATURE, NURTURE, AND HUMANDIVERSITY

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Psychology, Tenth Edition (Myers, D. G.)

1 BEHAVIOR GENETICS: PREDICTING INDIVIDUAL DIFFERENCES

2 EVOLUTIONARY PSYCHOLOGY: UNDERSTANDING HUMAN NATURE

3 HOW DOES GENDER INFLUENCE DEVELOPMENT?

4 CULTURAL INFLUENCES

5 GENDER DEVELOPMENT

6 REFLECTIONS ON NATURE AND NURTURE

NATURE, NURTURE, AND HUMAN DIVERSITY

LEARNING OBJECTIVES

• Discuss how the major components of human chromosomes function

• Discuss how twin studies can be used to determine whether human traits and psychological behavior are more heavily influenced by the environment or by heredity.

• Provide scholarly explanations for how identical twins can differ physically and psychologically

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• Discuss how molecular genetics research can be used to prevent the onset of specific psychological disorders

• Discuss how heredity and environment work together

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NATURE, NURTURE, AND HUMAN DIVERSITY

LEARNING OBJECTIVES

• Discuss how the field of epigenetics can help to explain the onset or prevention of specific genetic expressions

• Discuss how evolutionary psychologists use natural selection to explain similar human behavior tendencies

• Discuss how early experiences modify the human brain

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• Discuss how cultural norms influence human behavior

• Discuss what is included in the biopsychosocial approach to development

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NATURE, NURTURE, AND HUMAN DIVERSITYCH

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PREDICTING INDIVIDUAL DIFFERENCES

BEHAVIOR GENETICS:

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BEHAVIOR GENETICS: PREDICTING INDIVIDUAL DIFFERENCESCH

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What are genes and how do behavior geneticists explain ourindividual differences?

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• Behavior geneticists study human differences and weigh the effects and interplay of heredity and environment.

• behavior genetics: the study of the relative power and limits of genetics and environmental influences on behavior

• environment: every nongenetic influence, from prenatal nutrition to the people and things around us

© T.G. Lane 2014

1 GENES: OUR CODES FOR LIFE

• In humans, each cell normally contains 23 pairs (totaling 46) of chromosomes– each chromosome is composed of DNA. Genes make up a small segment of the giant DNA molecules.

• chromosomes: threadlike structures made of DNA molecules that contain the genes

• DNA: complex molecule containing the genetic information that makes up the chromosomesCH

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BEHAVIOR GENETICS: PREDICTING INDIVIDUAL DIFFERENCES

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1 GENES: OUR CODES FOR LIFE

• genes: the biochemical units of heredity that make up the chromosomes which is a small segment of DNA

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BEHAVIOR GENETICS: PREDICTING INDIVIDUAL DIFFERENCES

Human genome researchers have discovered the common sequence within human DNA; they are interested in occasional variations found at particular genes sites in human DNA

• genome: complete instruc- tions for making an organism, consisting of all the genetic material in that organism’s chromsome

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1 TWIN AND ADOPTION STUDIES

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Identical Versus Fraternal Twins

BEHAVIOR GENETICS: PREDICTING INDIVIDUAL DIFFERENCES

How much is a trait determined by our genes?

COM

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(genetics vs. environment)

Fraternal Twins

Identical Twins

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1 TWIN AND ADOPTION STUDIES

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Identical Versus Fraternal Twins

BEHAVIOR GENETICS: PREDICTING INDIVIDUAL DIFFERENCES

Identical Twins

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Fraternal Twins

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Identical Twins

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Twin studies compare several pairs of identical twins with fraternal twins to determine whether traits result from environmental or genetic factors

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1 TWIN AND ADOPTION STUDIES

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Identical Versus Fraternal Twins

BEHAVIOR GENETICS: PREDICTING INDIVIDUAL DIFFERENCES

• The fact that both identical twins in a pair do not possess a trait or develop a particular disease 100% of the time indicates that there are other factors involved

• Twins share many aspects of their environment (e.g., uterine environment, parenting style, education, wealth, culture, etc.) by virtue of being born in the same time and place; environ-mental differences can exist

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1 TWIN AND ADOPTION STUDIES

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Separated Twins/Biological Versus Adoptive Relatives

BEHAVIOR GENETICS: PREDICTING INDIVIDUAL DIFFERENCES

Identical Twins

DIFFERENTENVIRONM

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• In some domains it appears as though identical twins reared apart are just as similar as identical twins reared toget-her (i.e., sharing similar interests, habits, etc.)

• Studies indicate that people who grow up together, whether biologically related or not, do not much resemble one another in personality – suggesting genetics as the influence; parents do influence children’s attitudes, values, manners, faith, and politics

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1 TWIN AND ADOPTION STUDIES

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Temperament

BEHAVIOR GENETICS: PREDICTING INDIVIDUAL DIFFERENCES

Heredity predisposes one’s temperament within the first few weeks of birth

• temperament: emotional reactivity and intensity; emotional excitability inhibited

Temperament tends to remain consistent throughout childhood and in some cases throughout adulthood; environmental factors may change this aspect of one’s personality

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1 THE NEW FRONTIER: MOLECULAR GENETICS

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BEHAVIOR GENETICS: PREDICTING INDIVIDUAL DIFFERENCES

What is the promise of molecular genetics research?2:

Behavior geneticists are interested in molecular genetics for determining which specific genes influence behavior

• molecular genetics: the subfield of biology that studies the molecular structure and function of genes

Behavior geneticists aim to use DNA to predict risk (like diseases) so that steps can be taken to preventproblems (such as specific environmentalfactors) before they happen

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• stomach-to-brain (“I’m full”)• amount of fuel the muscles need• number calories are burned off by

being active• efficiency of the body of converting

extra calories into fat

BODY WEIGHT (several genes have influence)

BEHAVIOR GENETICS: PREDICTING INDIVIDUAL DIFFERENCES

Most human traits are influenced by teams of several genes, not by one gene alone

THE NEW FRONTIER: MOLECULAR GENETICS

Example:

Could DNA-scanning techniques lead parents to discriminate against their children (e.g. boys vs. girls, learning disability)?

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1 GENE-ENVIRONMENT INTERACTION

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BEHAVIOR GENETICS: PREDICTING INDIVIDUAL DIFFERENCES

How do heredity and environment work together3:

• Some human traits are expressed (activated) only in particular environments; genes react (e.g. similar to a butterflies’ genetic switch to change colors during different seasons)

• Nature and nurture interact; environments trigger genetic activity

• Genes for depression do not cause depression but instead regulate neurotransmitters involved in depression which can be thrown off by environmental circumstances

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Genes can be either active (expressed) or inactive (switched on or off); epigenetics aims to investigate how genes are triggered

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• epigenetics: the study of influ-ences on gene expression that occur without a DNA change

BEHAVIOR GENETICS: PREDICTING INDIVIDUAL DIFFERENCES

GENE-ENVIRONMENT INTERACTION

An organic methyl molecule is a type of epigenetic mark attaches to part of a DNA strand (instructs the cell to ignore any gene present in that DNA stretch– making it inactive) – e.g. stress hormones blocked

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BEHAVIOR GENETICS: PREDICTING INDIVIDUAL DIFFERENCES

GENE-ENVIRONMENT INTERACTION

Molecular geneticists are teamingwith psychologists to pinpointgenes that put people in risk forsuch genetically influence dis-orders like:

• learning disabilities• depression• schizophrenia• alcohol dependence

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UNDERSTANDING HUMAN NATURE

EVOLUTIONARY PSYCHOLOGY:

NATURE, NURTURE, AND HUMAN DIVERSITY

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EVOLUTIONARY PSYCHOLOGY: UNDERSTANDING HUMAN NATURE

NATURAL SELECTION AND ADAPATATION

How do evolutionary psychologists use nature selection to explainbehavior tendencies?

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Evolutionary psychologists focus mostly on what makes humans so much alike.

• evolutionary psychology: the study of the evolution of behavior and the mind, using principles of natural selection

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EVOLUTIONARY PSYCHOLOGY: UNDERSTANDING HUMAN NATURE

NATURAL SELECTION AND ADAPATATION

• natural selection: the principle that, among the range of inherited trait variations, those that lead to increased reproduction and survival will most likely be passed on to succeeding generations

• mutation: a random error in gene replic-ation that leads to

change

Human’s adaptive flexibility in responding to different environments contributes to one’s fitness– one’s ability to survive and reproduce

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EVOLUTIONARY PSYCHOLOGY: UNDERSTANDING HUMAN NATURE

NATURAL SELECTION AND ADAPATATION

Examples

• Pregnant women avoiding bitter, strong flavored, novel foods (toxic to embryonic development)

• “Universal moral grammar” (e.g. vent with lethal gas leak)

• Love for sweets and fats, which prepare human ancestors to survive famines

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HOW DOES EXPERIENCE

NATURE, NURTURE, AND HUMAN DIVERSITY

INFLUENCE DEVELOPMENT?

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HOW DOES EXPERIENCES INFLUENCE DEVELOPMENT?3

How do early experiences modify the brain?5:

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EXPERIENCE AND BRAIN DEVELOPMENT

• Human genes dictate one’s overall brain architecture, but ex-perience fill in the details, developing neural connections and preparing one’s brain for thought and language and other later experiences; touch also benefits premature babies

Use it or lose it.

• Both nature and nurture sculpt human synapses

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CULTURAL INFLUENCES

NATURE, NURTURE, AND HUMAN DIVERSITY

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CULTURAL INFLUENCES4

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How do cultural norms affect our behavior?6:

VARIATIONS ACROSS CULTURES

• Nature’s great gift to humans is one’s ability to learn and adapt. Depending on the circumstances, humans may need to be able to adapt to different cultures.

• culture: the enduring behaviors, ideas, attitudes, values, and traditions shared by a group of people and transmitted from one generation to the next

• Human nature manifests human diversity

• Culture shapes human lives

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CULTURAL INFLUENCES4

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• norms: an understood rule for accepted and expected behavior; prescribes “proper” behavior

• Individuals may exper-ience culture shock when they don’t understand what’s expected or accepted

Humans in varied cultures share some basic moral ideas yet each cultural group also evolves its own norms.

VARIATIONS ACROSS CULTURES

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CULTURAL INFLUENCES4

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Similarities Across Cultures:

Mindful of how others differ from us, individuals often fail to notice the similarities predisposed by individuals’ shared biology.

DEVELOPMENTAL SIMILARITIES ACROSS GROUPS

• personality traits (i.e., conscientiousness and extraversion)

• supported children feel better about themselves

• academic achievement• biological attributes and needs (e.g.,

language, hunger, etc.)

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GENDER DEVELOPMENT

NATURE, NURTURE, AND HUMAN DIVERSITY

© T.G. Lane 2014

GENDER DEVELOPMENT5 GENDER SIMILARITIES AND DIFFERENCES

DIFFERENCES SIMILARITIES

- overall self-esteem

- facing similar adaptive challenges (e.g. intelligence, learning, memory)

- tend to seek understanding from one’s mother when expressing worry and hurt

- women are doubly vulner- able to depression and anxiety

- men tend to be more agg- ressive

- women tend to use conver- sation to explore relationships; men tend to use conversation to explore solutions

- women tend to feel better about their behavior and ethics

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- men are more susceptible to alcoholism and suicide

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THE NATURE OF GENDER: OUR CULTURE

GENDER DEVELOPMENT

How do gender roles and gender typing influence gender dev-elopment?

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Although biologically influenced, gender is also socially constructed.

• Roles are often defined by society (e.g. gender roles); these behaviors are expected of those who occupy a particular social position

• gender roles: a set of expected behaviors for men and women

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THE NATURE OF GENDER: OUR CULTURE

GENDER DEVELOPMENT

Some researchers suggest that the social learning theory is a good explanation for children’s learned gender identity, while others argue that modeling and rewarding of male-female differences aren’t enough to explain gender typing.

• gender roles: a set of expected behaviors for males or for females• gender typing: the acquisition of a traditional masculine or feminine role

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NATURE AND NURTURE

REFLECTION ON

NATURE, NURTURE, AND HUMAN DIVERSITY

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What is included in the biopsychosocial approach to development?8:

REFLECTIONS ON NATURE AND NURTURE

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