Nature vs. Nurture: Behavioral Genetics and the Law

1. Nature vs. Nurture:Behavioral Genetics and the Law By Kathryn Baker

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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)

8. 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

9. 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”

10. 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?

11. 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.