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Nature vs. Nurture: Behavioral Genetics and the Law. By Kathryn Baker. 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 person’s life experiences

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Presentation Transcript
the gene x environment interaction
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 person’s 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
what is maoa
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
the dunedin study testing the effects of maoa
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
the numbers
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 group’s violent crime convictions
  • 85% of maltreated males with low levels of MAOA activity developed antisocial behaviors
court cases
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
court cases continued
Court Cases Continued
  • State v. Payne: expert testimony introduced about Payne’s 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)
what is slc6a4
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
genotyping defendants
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”
implications and questions
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?
resources
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.