Nature vs. Nurture: Behavioral Genetics and the Law

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Nature vs. NurtureBehavioral Genetics and the
Law

• By Kathryn Baker

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The Gene x Environment Interaction

• The formula for how genetics and life experiences
  influence a person
• Many professionals believe that violent behavior
  is linked to a persons life experiences
• Research is being done on many fronts to help the
  courts deal with new discoveries regarding the
  human genome and how it affects behavior

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What is MAOA?

• Monoamine Oxidase A a gene on the X chromosome
  codes for MAOA enzyme which, when there are low
  amounts, inactivates neurotransmitters like
  norepinephrine, serotonin, and dopamine
• Linked to the prevalence of anti-social and
  aggressive behavior in males who were maltreated
  as children

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The Dunedin Study Testing the Effects of MAOA

• Hypothesis that MAOA genotype can moderate the
  influence of childhood maltreatment on neural
  systems implicated in antisocial behavior
• Participants (3-11 years of age) 8 severely
  maltreated as children, 28 probable
  maltreatment, 64 no maltreatment
• Psychological assessment at age 26
• Summary of some results
• Males with high levels of MAOA activity were less
  affected by childhood maltreatment
• Conduct disorder more common among maltreated
  males with low levels of MAOA activity
• Violent crime convictions more common among
  maltreated males with low levels of MAOA activity

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The Numbers

• Approximately 80 of maltreated males with low
  levels of MAOA activity were reported to have
  conduct disorder
• Approximately 40 of maltreated males with high
  levels of MAOA activity were reported to have
  conduct disorder
• Maltreated males with low levels of MAOA activity
  made up 12 of the group BUT they accounted for
  44 of the groups violent crime convictions
• 85 of maltreated males with low levels of MAOA
  activity developed antisocial behaviors

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Court Cases

• Mobley v. State (1994) Mobley convicted of
  murder, armed robbery, aggravated assault and
  possession of a firearm wanted evidence
  presented that said he had deficient MAOA
  activity denied because it lacked scientific
  verifiability sufficient for it to be
  introduced executed on March 1, 2005
• State v. Sanders the serotonin defense low
  levels of serotonin led to an inability to
  control impulsive behavior denied during trial
  because It could not determine that he lacked
  the specific intent to kill only demonstrates
  that he was enraged when he did accepted during
  sentencing sentenced to life without parole

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Court Cases Continued

• State v. Payne expert testimony introduced about
  Paynes low levels of serotonin which suggested
  that he could not control an impulse once it
  had occurred jury found Payne guilty of
  second-degree rather than first-degree murder
  (Payne was also under the influence of cocaine
  and alcohol at the time of the crime)

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What is SLC6A4?

• The serotonin transport gene
• Short allele causes low transport activity the
  serotonin system is inefficient
• Low levels of activity could lead to depression
  in some individuals

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Genotyping Defendants

• AA High activity MAOA, short SLC6A4 allele
  expert testified AA had a genetic vulnerability
  to become depressed under severe stress found
  guilty of first-degree murder
• BB High activity MAOA long SLC6A4 allele
  expert testified that there were no genetic
  factors that might predispose BB to violence
  nobody objected to this testimony
• DD High activity MAOA heterozygous for SLC6A4
  court suggested that genetic testing could become
  necessary component of defense
• FF High activity MAOA short SLC6A4 allele
  court decided behavioral genetics was not yet
  scientific enough to present as testimony before
  a jury

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Implications and Questions

• Is this a sound defense against the death
  penalty A person should not receive the death
  penalty because his behavior was at least partly
  caused by his genetic makeup and his adverse life
  experiences?
• What about personal responsibility?
• The redefinition of normal. Does anyone who is
  normal commit a violent crime? Does every
  criminal have a genetic disorder will they in
  the future?
• Is evidence of genetic and behavioral interaction
  acceptable for defending the insanity defense?
• Not guilty by reason of insanity vs. Guilty but
  mentally ill.
• What types of punishment become acceptable?

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Resources

• Caspi, Avshalom et al. Role of Genotype in the
  Cycle of Violence in Maltreated Children.
  Science Vol. 297, 2002.
• Bernet, William et al. Bad Nature, Bad Nurture,
  and Testimony regarding MAOA and SLC6A4
  Genotyping at Murder Trials. J Forensic Science
  Vol. 52, No. 6, 2007.