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Nature V. Nurture


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Nature V. Nurture

  1. 1. Shedding some light on the debate Nature versus Nurture
  2. 2. Gene X Environment Interactions <ul><li>A GxE interaction exists when genetic differences influence individuals’ vulnerability to environmental experience </li></ul><ul><li>A GxE interaction is easily confused with passive or active gene-environment correlations. </li></ul>Jaffee, et. al., 2004.
  3. 3. <ul><li>A passive gene-environment correlation exists because parents provide children with both genotypes and environment. </li></ul><ul><li>Passive G-E correlations are actually genetic influences that occur in the presence of a (spurious) environmental correlate. </li></ul>Passive G-E Correlations
  4. 4. Passive G-E Correlations <ul><li>Example: adult antisocial behavior could be heritable. So when an adult exhibits ASB by maltreating a child, the child also has conduct disorder genetically through heritable ASB. </li></ul><ul><li>This might look like an environmental effect of maltreatment, but it actually could be genes that account for both the adult’s abusive behavior and the child’s conduct disorder. </li></ul>
  5. 5. Active G-E Correlations <ul><li>An active gene-environment correlation exists when a child elicits responses from the environment. </li></ul><ul><li>Active G-E correlations are actually genetic influences of the child, when the genes of the child act to influence the environment of the child. </li></ul>
  6. 6. Active G-E Correlations <ul><li>Example: a child’s genes lead the child to misbehave and invoke physical discipline from an otherwise non-violent parent. </li></ul><ul><li>If the child has conduct disorder, this might look like the environmental effect of physical discipline, but the child’s genes actually caused both the conduct disorder and the physical discipline. </li></ul>
  7. 7. Testing for a GxE Interaction <ul><li>When testing for an GxE interaction it is important to rule out both active and passive G-E correlations to find a true interaction effect. </li></ul><ul><li>Of course, you must also rule out simple genetic influences as well as simple environmental influences. </li></ul>
  8. 8. GxE and Aggression <ul><li>Several studies have linked aggressive behavior and aggression-related psychological disorders to GxE interactions. </li></ul><ul><li>Other studies have found GxE interactions that affect aggression-related neurotransmitters. </li></ul>
  9. 9. GxE in Rhesus Monkeys <ul><li>Genotype and early rearing experience interact to affect 5-HT functioning. </li></ul><ul><li>Peer-reared monkeys has reduced 5-HT functioning, but only if they had at least one short allele for the gene in question. </li></ul><ul><li>This study does not link specifically to aggression, but reduced 5-HT is often linked to aggressive behavior and pathology. </li></ul>Bennett et. al., 2002
  10. 10. 5-HT in Humans <ul><li>GxE found to influence depression in humans, through stress and 5-HT transporter gene. </li></ul><ul><li>Links life stress to depression and suicidality, but only for individuals with a risky 5-HT genotype. </li></ul><ul><li>This study also does not link specifically to aggression. </li></ul>Caspi et. al., 2003
  11. 11. GxE for Conduct Disorder <ul><li>This twin study found that childhood physical maltreatment led to antisocial behavior and/or conduct disorder most consistently among genetically vulnerable children. </li></ul><ul><li>Did not measure any specific genotype. </li></ul>Jaffee et. al., 2005
  12. 12. MAOA Gene and Child Abuse <ul><li>This is the study mentioned earlier in lecture. </li></ul><ul><li>Found a specific gene relating child abuse to adult aggression: low- vs. high-activity MAOA genes. </li></ul><ul><li>MAOA genes affect function of 5-HT, norepinephrine and dopamine. </li></ul><ul><li>85% of maltreated males with low-activity MAOA gene developed antisocial behavior. </li></ul>Caspi et. al., 2002
  13. 13. MAOA Genes and Sex <ul><li>MAOA gene located on the X chromosome, so females are less likely to have only low-activity copies of the MAOA gene. </li></ul><ul><li>Maltreated girls with a low-activity gene were more likely to develop conduct disorder, so MAOA could also exert a protective influence in females. </li></ul><ul><li>This could partially explain the sex difference in aggression: females are more likely to have at least one copy of the protective high-activity MAOA gene and thus less likely to have the aggression-linked GxE of maltreatment and low-activity MAOA genes. </li></ul>Caspi et. al., 2002
  14. 14. Limits of Child Effects <ul><li>Children’s genetically influenced behavior elicits corporal punishment from adults, but not physical abuse. </li></ul><ul><li>Rules out the possibility that the relationship between conduct problems and maltreatment is due to genetic child effects. </li></ul><ul><li>In other words, it rules out the possibility of an active gene-environment correlation and confirms that this is a true GxE interaction. </li></ul>Jaffee et. al., 2004
  15. 15. Putting them all together… <ul><li>Combined, these studies provide evidence for two kinds of GxE interactions: </li></ul><ul><li>First, a GxE leading to aggressive behavior, through the effects of genotype and childhood maltreatment </li></ul><ul><li>Second, a GxE leading to changes in the functioning of important neurotransmitters that have been shown to affect aggression. </li></ul><ul><li>These articles this provide strong evidence for the belief that inappropriate aggression in humans is often caused by a GxE interaction. </li></ul>
  16. 16. Why GxE is better <ul><li>Many studies that find either genetic or environmental influences cannot be replicated consistently </li></ul><ul><li>This could be evidence of a GxE interaction, and differential exposure to genetic or environmental risk factors in different samples. </li></ul>
  17. 17. Why GxE is better <ul><li>The search for specific genes that influence behavior is more likely to be successful if environmental interactions are accounted for, rather than only looking for direct gene effects. </li></ul><ul><li>Studies might fail to find correlations between genes and behaviors because they do not look for interactions. </li></ul>
  18. 18. Why GxE is better <ul><li>GxE findings are causal and often more predictive than gene or environment alone. </li></ul><ul><li>GxE findings present a more complete picture of the causes of psychology disorders and symptoms of disorders. </li></ul><ul><li>GxE findings can be more useful for identifying at-risk populations and intervening with treatment. </li></ul>
  19. 19. <ul><li>Ignoring nurture can prevent geneticists from understanding nature, and…. </li></ul>Ignoring nature can prevent sociologists and social psychologists form understanding nurture.