Chapter 6: Genetics and Personality

Chapter 6: Genetics and Personality

• This chapter discusses the role of genetics in shaping personality.
• The study of genes and personality is a field with ongoing concerns and controversies.

Learning Objectives

• Understand the history and current state of the scientific study of genes and personality.
• Define and describe the primary goals and research methods of behavioral genetics.
• Outline the major findings of behavioral genetics research.
• Differentiate between shared and non-shared environmental influences.
• Summarize the insights from molecular genetics.
• Explain the interaction between genetic and environmental factors.

The Biological Domain

• A record of the past is stored in the genetic blueprint.

Genes and Personality

• A genome is the complete set of genes.
• The human genome contains approximately 20,000-30,000 genes located on 23 pairs of chromosomes.
• The Human Genome Project aimed to sequence the human genome, identifying the specific sequence of DNA molecules.
• Identifying the DNA sequence does not automatically reveal the function of each molecule.

Genes and Personality 2

• Most genes are the same for all humans.
• Small differences in genes exist between individuals, influencing physical traits and personality.

Controversy About Genes and Personality

• Behavioral geneticists investigate the role of genetics and environment in individual differences.
• This investigation is highly controversial, causing ideological concerns.
• There are concerns about renewed interest in eugenics.

Controversy About Genes and Personality 2

• Modern behavioral geneticists are cautious about the implications of their work.
• They are sensitive to ideological concerns.
• Understanding the genetic component of a trait does not make the environment powerless to modify it.

Sorting Science, Politics, and Values

• The environmentalist view suggests personality is mainly determined by socialization experiences.
• Controversies often arise regarding intelligence studies.
• Connecting science, politics, and values requires careful consideration.
• The scientific method is self-correcting.

Behavioral Genetics

• The field aims to determine the percentage of individual differences in a trait attributable to genetics versus the environment.
• It studies how genes and environment interact and correlate to produce individual differences, identifying where environmental effects occur (e.g., parental socialization, teachers).

Behavioral Genetics 2

• Studies confirm genetic influence on height.
• Roughly 90% of height differences are due to genetic factors, and 10% to environmental factors.

Behavioral Genetics 3

• Methods used in behavioral genetics can analyze any behavior trait.
• These methods include height, weight, intelligence, personality traits, and attitudes.
• Variability in individual traits, or differences, can be divided into percentages due to different causes.

What is Heritability?

• Heritability is a statistic measuring the proportion of observed variance in a group of individuals accounted for by genetic variance.
• Phenotypic variance refers to observed individual differences, such as height, weight, or personality.

What is Heritability? 2

• Genotypic variance refers to differences in the total collection of genes among individuals.
• Environmentality pertains to the portion of observed variance in a group of individuals attributable to environmental variance.

Misconceptions About Heritability

• Heritability cannot be applied to a single individual.
• Heritability is not unchanging or permanent.
• Heritability is not a precise statistic.

Nature-Nurture Debate Clarified

• Arguments about genes versus environment in determining personality are usually discussed at the group level rather than individual level.
• The influence of both genes and environment is only relevant when discussing group variation.

Research Methods in Behavioural Genetics

• Methods include selective breeding, family studies, twin studies, and adoption studies.

Selective Breeding

• Selective breeding studies animals, especially dogs, to examine the heritability of traits.
• This is not ethically applicable to humans.

Family Studies

• Family studies correlate the level of genetic overlap among family members with the degree of relatedness
• Family members with greater genetic relatedness are more similar on traits they share.
• Family studies have a problem because members of the same family often share the same environment, confounding genetic influences with environmental ones.

Twin Studies

• Twin studies estimate heritability by comparing identical (MZ) twins and fraternal (DZ) twins.
• If MZ twins are more similar than DZ twins, it suggests a genetic component.
• Twin studies assume equal environments for MZ and DZ twins; therefore it is useful to study twins reared apart and measure heritability this way
• Formulas calculate heritability.

Twin Studies 2

• The twin method assumes equal environments amongst twins.

Adoption Studies

• Adoption studies correlate traits in adopted children with adoptive and genetic parents.
• Provides evidence of environmental influence and genetic influence.
• Adoption studies overcome some issues of shared family environment.

Adoption Studies 2

• Selective placement is a problem for adoption studies
• Studies of twins reared apart combine the strengths of twin and adoption studies.

Major Findings from Behavioral Genetic Research

• Personality traits, attitudes and preferences, drinking habits and smoking habits have shown some degree of heritability, but the percentages of heritability vary.

Personality Traits

• Personality traits often studied in behavioral genetics include extraversion and neuroticism.
• Heritability estimates for major traits like extraversion, agreeableness, conscientiousness, neuroticism, and openness to experience typically fall within the 40-60 percent range.

Attitudes and Preferences

• Heritability of attitudes varies.
• Some attitudes (e.g., traditionalism) show high heritability (.60), while others have low or no heritability.

Drinking and Smoking

• Behavioral manifestations of personality traits, such as sensation-seeking, extraversion, and neuroticism show heritability.

Marriage

• Genes potentially affect the tendency to marry or stay single (68%).
• Genes contribute to marital satisfaction for women.

Shared Versus Nonshared Environmental Influences

• Studies showing moderate heritability also suggest the importance of environmental factors.
• Personality characteristics exhibit heritability percentages ranging from 40 to 60, showing the importance of the environment and non-shared variables (unique experiences of siblings).

Shared Versus Nonshared Environmental Influences 2

• Shared environmental influences: Features of the family environment shared by siblings (e.g., number of books in the home) have a similar effect amongst siblings.
• Nonshared environmental influences: Differences within the family in the environment affect siblings differently (e.g., friends, teachers).

Molecular Genetics

• Techniques are used to identify specific genes associated with personality traits.
• The D4DR gene, located on chromosome 11, is linked to dopamine receptor and implicated in some personality traits.

Molecular Genetics 2

• The D4DR gene and novelty seeking have frequently been studied.
• Individuals with the "long repeat" version of the D4DR gene are generally higher on novelty seeking than those with the "short repeat" version.
• Further research on this linkage continues to investigate the precise mechanisms and relationship.

Genes and the Environment

• The interaction and correlations between genes and the environment influence personality development.

Genotype-Environment Interaction

• Individuals with different genotypes respond differently to the same environmental stimuli, such as task performance in loud vs noisy conditions.

Genotype-Environment Correlation

• Different genotypes are exposed to different environments.
• Genotype-environment correlations can be positive or negative.
• These correlations are categorized as passive, reactive, and active.

Genotype-Environment Correlation 2

• Passive correlations: Parents pass on both genes and the environment simultaneously to their children. (e.g., a child's verbal ability and the number of books in the home)

Genotype-Environment Correlation 3

• Reactive (Evocative) correlations: Parents or others respond to children differently based on their genotype. (e.g., baby's liking for cuddling and the mother's corresponding behavior)

Genotype-Environment Correlation 4

• Active correlations: Individuals actively seek environments that match their genes. (e.g., high sensation seekers choosing risky environments)

Epigenetics

• Epigenetics studies how environmental experiences influence how genes are expressed in organisms.
• Epigenetic processes concern chemical processes such as DNA methylation and histone modification.
• Research suggests epigenetic influences might play a role in anxiety & stress reactivity, and changes in childhood can impact adulthood.

Summary and Evaluation

• Empirical evidence supporting genetic influences has grown stronger through the use of behavioral genetics methods.
• Much environmental influence stems from non-shared experiences between siblings.
• The interaction between heritability and environmentality, as well as promising future research, including genotype-environment correlations, molecular behaviour genetic analysis and epigenetics remain key areas.

Explore the intersection of genetics and personality in this quiz based on Chapter 6. Understand key concepts in behavioral genetics, including the influence of genes and environment on personality traits. Delve into research findings and the role of the Human Genome Project in this fascinating field.