Shedding some light on the debate

Shedding some light on the debate

Nature versus Nurture

Gene X Environment Interactions

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.

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.

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.

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

Passive G-E CorrelationsPassive 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.

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.

Active G-E CorrelationsActive G-E

CorrelationsAn 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.

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.

Active G-E CorrelationsActive G-E

CorrelationsExample: 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.

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.

Testing for a GxE Interaction

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.

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.

GxE and AggressionGxE 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.

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.

GxE in Rhesus Monkeys

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.

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

5-HT in Humans5-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.

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

GxE for Conduct Disorder

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.

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

MAOA Gene and Child Abuse

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.

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

MAOA Genes and SexMAOA Genes and SexMAOA 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.

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

Limits of Child Effects

Limits of Child EffectsChildren’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.

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

Putting them all together…

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.

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.

Why GxE is betterWhy 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.

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.

Why GxE is betterWhy 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.

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.

Why GxE is betterWhy 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.

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.

Ignoring nurture can prevent geneticists from understanding nature, and….

Ignoring nurture can prevent geneticists from understanding nature, and….

Ignoring nature can prevent sociologists and social psychologists form understanding nurture.