8. Genes & Personality

What behavioural geneticists determine

the degree to which individual differences, including personality, are caused by genetic and environmental differences

Eugenics

The belief that we can design the future of the human species by promoting reproduction among individuals with desirable traits and discouraging reproduction among individuals without those traits.

Goals of behavioural geneticists

Determine the percentage of individual differences in a trait attributed to genetic differences and the percentage attributed to environmental differences

Determine the ways in which genes and environment interact and correlate with each other to produce individual differences.

Determine precisely where in the “environment”environmental effects exist—e.g., parental socialization, different teachers.

Heritability (in terms of behaviour)

The extent to which genetics predict behavior or traits.

Inherited

behaviour or trait is determined by genes alone.

Heritability (in terms of variance)

The proportion of observed variance in a group of individuals that can be accounted for by genetic variance.

Phenotypic Variance

The observed individual differences in a trait.

Genotypic Variance

Genetic variance that is responsible for individual differences in the phenotypic expression of specific traits.

Environmentality

Percentage of observed variance in a group of individuals that can be attributed to environment.

Family studies

Correlates the degree of genetic overlap among family members with the degree of similarity in personality trait.

Twin Studies

Studies that compare the similarities between monozygotic (identical) twins and dizygotic (fraternal) twins to determine the relative contributions of genetics and environment to a trait.

Twin Studies Heritability Estimates

Because Monozygotic twins share same genes, differences in phenotypes (traits) can only be attributable to “environment”.

Differences in phenotypes between pairs of Dizygotic twins can be attributable to different genes or different“environment”

Shared Environment

The aspects of the environment that are shared by siblings in a family.

e.g., Kids in same family have same SES, go to same schools, share same childrearing.

Nonshared Environment

The aspects of the environment that differ across siblings in a family.

e.g., different friends, different teachers, different relationship with parents.

Adoption Studies

Studies that compare the similarities between adopted children and their genetic and adoptive parents to determine the contributions of genetics and environment to a trait.

Heritability Estimates

Quantitative measures that range from 0.0 to 1.0, indicating the proportion of variability in a trait that can be attributed to genetic differences.

Genotype-Environment Interaction

People with different genotypes respond differently to the same environments.

Types of genotype-environment correlations

–       Passive: Parents provide genes and environment, kid does nothing e.g., Parents choosing number of books in home

–       Reactive: Kid behaviour, parent reacts to specific genotype e.g., Kid likes reading, parents give kid more books or take the kid to the library more often

–       Active: Kid with particular genotype seeks out environments e.g., Kid chooses to spend time in libraries