The document discusses gene-environment interactions (GxE) and how they relate to aggression. It provides several examples of studies finding GxE effects on aggression-related behaviors and neurotransmitter functioning. Specifically, it finds that childhood maltreatment leads to aggression in genetically vulnerable individuals, and that early life stress can interact with serotonin-regulating genes to increase depression risk. Accounting for GxE is important as it provides more accurate and predictive models than examining genes or environment alone. Understanding these interactions is crucial for identifying at-risk groups and developing effective interventions.

1. Shedding some light on the debate Nature versus Nurture

2. Gene X Environment Interactions A GxE interaction exists when genetic differences influence individuals’ vulnerability to environmental experience A GxE interaction is easily confused with passive or active gene-environment correlations. Jaffee, et. al., 2004.

3. A passive gene-environment correlation exists because parents provide children with both genotypes and environment. Passive G-E correlations are actually genetic influences that occur in the presence of a (spurious) environmental correlate. Passive G-E Correlations

4. Passive G-E Correlations 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. 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.

5. Active G-E Correlations An active gene-environment correlation exists when a child elicits responses from the environment. 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.

6. Active G-E Correlations Example: a child’s genes lead the child to misbehave and invoke physical discipline from an otherwise non-violent parent. 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.

7. Testing for a GxE Interaction 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. Of course, you must also rule out simple genetic influences as well as simple environmental influences.

8. GxE and Aggression Several studies have linked aggressive behavior and aggression-related psychological disorders to GxE interactions. Other studies have found GxE interactions that affect aggression-related neurotransmitters.

9. GxE in Rhesus Monkeys Genotype and early rearing experience interact to affect 5-HT functioning. Peer-reared monkeys has reduced 5-HT functioning, but only if they had at least one short allele for the gene in question. This study does not link specifically to aggression, but reduced 5-HT is often linked to aggressive behavior and pathology. Bennett et. al., 2002

10. 5-HT in Humans GxE found to influence depression in humans, through stress and 5-HT transporter gene. Links life stress to depression and suicidality, but only for individuals with a risky 5-HT genotype. This study also does not link specifically to aggression. Caspi et. al., 2003

11. GxE for Conduct Disorder This twin study found that childhood physical maltreatment led to antisocial behavior and/or conduct disorder most consistently among genetically vulnerable children. Did not measure any specific genotype. Jaffee et. al., 2005

12. MAOA Gene and Child Abuse This is the study mentioned earlier in lecture. Found a specific gene relating child abuse to adult aggression: low- vs. high-activity MAOA genes. MAOA genes affect function of 5-HT, norepinephrine and dopamine. 85% of maltreated males with low-activity MAOA gene developed antisocial behavior. Caspi et. al., 2002

13. MAOA Genes and Sex MAOA gene located on the X chromosome, so females are less likely to have only low-activity copies of the MAOA gene. Maltreated girls with a low-activity gene were more likely to develop conduct disorder, so MAOA could also exert a protective influence in females. 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. Caspi et. al., 2002

14. Limits of Child Effects Children’s genetically influenced behavior elicits corporal punishment from adults, but not physical abuse. Rules out the possibility that the relationship between conduct problems and maltreatment is due to genetic child effects. In other words, it rules out the possibility of an active gene-environment correlation and confirms that this is a true GxE interaction. Jaffee et. al., 2004

15. Putting them all together… Combined, these studies provide evidence for two kinds of GxE interactions: First, a GxE leading to aggressive behavior, through the effects of genotype and childhood maltreatment Second, a GxE leading to changes in the functioning of important neurotransmitters that have been shown to affect aggression. These articles this provide strong evidence for the belief that inappropriate aggression in humans is often caused by a GxE interaction.

16. Why GxE is better Many studies that find either genetic or environmental influences cannot be replicated consistently This could be evidence of a GxE interaction, and differential exposure to genetic or environmental risk factors in different samples.

17. Why GxE is better 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. Studies might fail to find correlations between genes and behaviors because they do not look for interactions.

18. Why GxE is better GxE findings are causal and often more predictive than gene or environment alone. GxE findings present a more complete picture of the causes of psychology disorders and symptoms of disorders. GxE findings can be more useful for identifying at-risk populations and intervening with treatment.

19. Ignoring nurture can prevent geneticists from understanding nature, and…. Ignoring nature can prevent sociologists and social psychologists form understanding nurture.