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PSYC 2740
David Stanley

1 PSYC*2740-01 January 30, 2013 The Biological Domain: Genetics & Personality Genes and Personality: Issues and Controversy Why might the study of genes and personality be controversial? 1) Ideology: the fear that if we do establish genes that affect certain personality factors, then genes might be used to explain everything or people will not use genes to explain any of the factor. People are also afraid that police systems will be driven to base a lot of their information on genetics. Therefore, political agendas might be driven by these findings. 2) Eugenetics: the controversy regarding using eugenetics to knockout specific traits. Percent of Variance: There are differences between people due to a certain cause (in percentages). Many times this is used to look at what percentage of a personality trait is a product of genetics or the environment. These percentages are not concrete however, there might be errors or differences between different studies. Heritability vs. Environmentality Heritability: amount of phenotypic variance in a group due to genotypic variance. Genotypic variance: individual differences in people’s genes. Environmentality: amount of observed variance due to the environment. Behavioural genetics methodologies Family studies If personality traits are heritable, you should see personality traits across generations of a family. In family studies, you examine correlations between genetic relatedness of family members and personality similarity. Within families, there is a percent of shared genes. Between parents and children, and children and their siblings, there is 50% shared genes. Between grandparents and grandchildren, there is 25%. Closer relatives should have more personality similarity. Twin studies In twin studies, we look at monozygotic and dizygotic twins. We estimate heritability via the similarity of monozygotic versus dizygotic twins. We use the heritability formula (which is the difference between the correlations between), which is Heritability (squared) = 2(rmz – rdz), where rmz = correlation between monozygotic twins for a trait, and rdz = correlation between dizygotic twins for a trait. When we make predictions based on findings from twin studies, we must make some critical assumptions. First, we assume equal environments for both monozygotic and dizygotic twins. Although there will be some differences in even the way parents treat different kinds of twins, there usually won’t be a difference that would meaningfully impact the results of these studies. Another critical assumption is that the twins should be a representative of the general population. Adoption Studies 2 In adoption studies, we examine the correlations between adopted children and adoptive parents. We can also get information from the birth parents and look at the correlations between the children and their adoptive parents, and the children and their birth parents. We compare these two correlations to see how environmentability and heritability has affected these children. Some limitations of adoption studies are that we make an assumption of representativeness, but the question is whether the children and parents represent the general population? The other limitation is selective placement, which is when adoptive children are placed with parents similar to their birth parents. Luckily, this has not been a major issue and is unlikely to happen, however, we must look at the limitations as well. Twins Raised Apart This method combines the strengths of twin and adoption studies where heredity is equal to the correlation of the trait between the twins. Major Findings: Big 5 Traits The Big Five is a general trend found across many different studies. The Big Five is found to have a moderate heritability of about .50. This tells us that on the one hand, heritability does play a role, but it also means that environment plays an additional role. Major Findings: Divorce Divorce is found to be higher in monozygotic versus dizygotic twins (suggests that divorce is partially genetic) About fifty percent of the variance in divorce is due to genetic influence. Divorce stems from traits that partners bring to a marriage (the traits that each person bring to the relationship are more important). Major Findings: Smoking and Drinking Neuroticism (these behaviours may be used to reduce levels of anxiety), extraversion (is a social thing, people drink and smoke in a social setting), and sensation seeking are all associated with smoking and drinking. There is moderate heritability for smoking and drinking habits, however, there is more heritability for alcoholism versus daily drinking habits. This is consistent across sexes. Major Findings: Gender Identity Disorder (GID) Diagnosis: 1) Cross-gender identification 2) Psychological discomfort with one’s biological sex Gender Identity is quite heritable (.62). There is speculation about it being neurological. People with this diagnosis are really susceptible to depression, victimization, and anxiety. There is also still controversy regarding it being a diagnosis. Shared vs. Nonshared Environmental Influences Generally, non-shared experiences and environments yield the differences in personalities, rather than shared environmental influences. Analyzing How Genes and Environment Interact Genotype-environment Interaction The main thing that needs to be analyzed here is when you have a differential response of individuals with different genotypes to similar environments. 3 For example, children who have experienced abuse and have low monoamine oxidase A are found to be more anti-social and violent. However, children who experience abuse but have high levels of monoamine oxidase A are found to be less anti-social and less violent. Genotype-Environment Conditions This looks at differential exposure of individuals with different genotypes to different environments. There are three types of genotypes: passive, reactive, and active. Passive correlations: parents provide both genes and environment to the children. Reactive correlation: parents or others respond to children differently, based on children’s genotype. This is where the genotype is affecting what type of environment the child is exposed to. For example, a very self-conscious person will have people react to them with sensitivity. Active correlation: person with a particular genotype creates a particular environment. Here, the person is actively seeking their own environment, or are niche-picking. Molecular Genetics These are methods designed to identify specific genes linked with specific traits. For example, there are found to be longer D4DR strains in novelty seeking. Neuroticism (and depression) may be linked to the serotonin transporter gene (5-HTT). Physiological Approaches to Personality Build a Theoretical Bridge… (see how personality and physiology relate) We can look at specific conditions or stimulus (e.g., an audience) If we use this example to look at the personality trait of shyness, the psychological response would be anxiety. We could find a physiological indicator of this response (for example, heart rate increase). We could also look at behavior as an indicator of the psychological response (for example, avoidance or running away). Common
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