The Gene Pool Metaphor
Criminal Genes and The Law



Criminal Genes and the Law

    The primary use of genetics in criminal law is for identification of defendants, such as in a rape case, and as a defense to exculpate or provide mitigating reasons for a crime.

    All crimes have several basic elements.  First, the defendant must have committed a voluntary act (“actus reus”).  This reflects the primary concern of criminal law with intentional conduct, rather than a person’s thoughts or involuntary acts.  A guilty thought is not punishable but a guilty act is.  Secondly, a defendant must have a culpable intent (“mens rea”).  Mens rea represents the requirement that a person possess a “culpable state of mind” to be punished for a crime.  This means that a person must have acted purposely or knowingly in committing the act.  The culpability requirement is related to the punitive nature of criminal law.  Criminal liability is rarely imposed without a criminal state of mind.  An underlying principle of the criminal system is that the threat of punishment will deter crime.  An individual who acts without knowledge or intent is plainly beyond the deterrent force of the law.  A person who is punished must be blameworthy for the criminal act.

    What happens when a criminal defendant has made a mistake of fact or law?  Under the Model Penal Code, ignorance or mistake as to a matter of fact or law is a defense only when it negates the mens rea required to establish a crime.

    Negligent or reckless behavior can be sufficient to infer mens rea.  When a criminal defendant consciously disregards a substantial and unjustifiable risk, his behavior may establish a culpable state of mind.  When a person, who is intoxicated with alcohol or another drug which impairs mental and physical abilities, gets behind the wheel of a car, strikes and kills a person, he can be found guilty of manslaughter, even if he did not intend to commit that act.  This supposes an awareness of the creation of a substantial homicidal risk that has been ignored by the actor.

    Is a person culpable for his conduct when he has a genetic disease that is responsible for his criminal behavior? Consider the following case.  John Wilson had been in trouble with the law since a teenager.  He had served prison time on several different occasions for assault, burglary, and disorderly conduct.  One night, Wilson had been out drinking at a bar when he stopped off at all night convenience store.  Wilson took a bottle of soda to the cash register, but before paying for it, he pulled out a gun from his jacket, and pointed it at the store clerk, ordering him to empty the money in the cash register into a brown paper bag.  The clerk followed Wilson’s directions, filling the bag with the contents of the register.  Wilson was sure that there was another money stash, having seen clerks reach below the register in previous visits to the store.  When the clerk denied any knowledge of it, Wilson become very angry, believing that he was being lied to and disrespected.  He walked the clerk to the back of the store.  Forcing the clerk to kneel on the ground, Wilson placed his gun behind the base of the clerk’s skull, and fired the gun.  The clerk was killed instantly.  Wilson fled.  Two days later, Wilson was arrested when he was pulled over for speeding and the police found the murder weapon on the car floor.

    At the murder trial, Wilson’s attorney claimed that Wilson did not have a culpable state of mind.  Instead, he called a medical geneticist to the stand who testified that Wilson had a genetic X-linked condition characterized by mild mental retardation and aggressive, sometimes violent, behavior.  Four generations of males in Wilson’s had manifested this genetic disorder.  Two of Wilson’s uncles were in prison at the time of his act and his grandfather had received the death penalty in a capital murder case.  The geneticist argued that Wilson had not acted voluntarily in committing the act.  Rather, his genetic disorder had compelled him to commit violent acts.  Alcohol, he said, induced violent behavior in Wilson, as it did all afflicted family members.

    The issue raised by the hypothetical Wilson case is intriguing in view of recent scientific research which has identified numerous links between gene and behaviors.  Various gene alleles have been identified which are associated with pathological behaviors.  A genetic basis has been established for a variety of human behaviors, including aggression, anxiety, and depression.  If it is true that one’s genes shape, or even control, one’s behavior, how should such facts square with the criminal system?  The purpose of criminal law is to punish a person for a voluntary, culpable act.  Suppose it is proved beyond doubt that a particular gene is responsible for a defendant’s aggressive behavior.  Is it fair to hold that person accountable for his act?  One of the central issues is to distinguish between propensity and causality.  Mr. Wilson’s genetic disorder may have made it more likely that he would commit a violent act, but did it directly produce the criminal conduct.  What if an aggressive behavior was a response to an emotional stress or environmental cue?  In Wilson’s case, the medical expert testified that alcohol incited Wilson to violence.  Is he culpable for his crime because he voluntarily and recklessly took an alcoholic drink and knew, or should have known, that it would arouse violent behavior?

    One of the functions of the criminal system is to punish a person for criminal acts.  Traditionally, several explanations have been offered for the punishment requirement: (1) deterrence; (2) incapacitation or isolation of the guilty person from society; (3) rehabilitation; and (4) retribution.  Should the terms of punishment take into account the causality between the crime and an individual’s biological status?  In the Wilson case, the defense team argued that Wilson was not responsible for his conduct because he had a genetic disorder that caused him to commit violent acts.  One of the difficulties of Wilson’s argument is establishing direct causality between the act and the genetic defect.  A more reasonable formulation may ask what the probability is that an individual with a particular genotype will lead to criminal conduct.  If it is 100%, do we let him off on the grounds that either the act was not voluntary or he could not have possessed mens rea because of the genetic defect?  If the defect only establishes a propensity to criminal activity, say 20%, then should his punishment be adjusted accordingly.

    These issues are not new to the criminal system. According to Section 4.01(1) of the Modern Penal Code:  “A person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he lacks substantial capacity either to appreciate the criminality [wrongfulness] of his conduct or to conform his conduct to the requirements of law.”  The rationale is that punishing a person who, as a result of mental disease or defect, is incapable of understanding that their conduct is of such nature to merit punishment, or is substantially incapable of refraining from criminal conduct, does not further the objective of the criminal system to deter potential offenders from the commission of a crime.  The purpose of 4.01(1) is to identify those individuals whose behavior would not be intimidated by the threat of punishment, and whose punishment would not deter others.  Does this legal test distinguish the nondeterrables from those who are merely mentally-disordered, but understand the nature of their conduct?  Now that genetic bases for mental disease have been identified would it be better to use a genetic test?

The People of The State of New York, Plaintiff, v. Charles Yukl, Defendant, 83 Misc 2d 364; 372 N.Y.S.2d 313 (1975, Supreme Court of NY, NY County)
Stephen A. Mobley v. The State, 265 Ga. 292; 455 S.E.2d 61 (Supreme Court of Georgia, 1995)

(1) A genetic map of the human genome is a map of the chromosomes having polymorphic DNA markers at determined intervals.  A polymorphism means that different sequences of DNA are found in the population at the same locus.  The utility of such a map is to facilitate the localization of disease and behavior genes by family-linkage and population studies.  Hoffman, Am J Hum Gen, 54:129 (1994); Marshall, Science, 274:488 (1996); Lander, Science, 274:536, 1996.

(2) The report referred to in Mobley was a study of Dutch family in the Netherlands.  The author of the report, Dr. Han G. Brunner, a medical geneticist, had been contacted by a woman who sought help for a problem in her family.  For generations, many of the men in her family had been prone to violent and unprovoked aggressive attacks.  The problem had been so severe that an unaffected maternal grandmother had collected detailed information about nine men in the family who displayed the aberrant, apparently inherited, behavior.  One affected male had been convicted of the rape of his sister.  Another affected male had attempted to run his boss over with a car.  A third affected male would enter his sisters’ bedrooms at night, armed with a knife, and force them to undress.  Two of the family members were convicted arsonists.  Brunner and his colleagues performed DNA analysis of tissue samples of 24 members of the family.  A DNA marker was identified on the X-chromosome which was present in affected males but not in unaffected males.  The DNA marker was located at the locus of the structural gene for monoamine oxidase a (“MAOA), an enzyme involved in the metabolism of the monoamine neurotransmitters dopamine, serotonin, epinephrine, and norepinephrine. Affected males also displayed a marked disturbance in monoamine metabolism, suggesting that MAOA was defective.  Brunner et al., A. J. Hum. Genet., 52:1032-1039, 1993; Morell, Science, 260:1722-1723, 1993.

(3) Turpin v. Mobley, 269 Ga. 635; 502 S.E.2d 458 (Supreme Court of Georgia, 1998).  Mobley appealed the death sentence on the grounds that his trial counsel Summer had been ineffective in the preparation for and conduct of the sentencing phase.  While preparing Mobley’s defense, Summer had read an article describing Brunner’s research establishing a connection between antisocial and violent behavior with a genetic defect in the MAOA gene.

“Summer investigated the use of this genetic link to violence as a possible mitigation defense. He contacted a professor of genetics at Harvard Medical School and reviewed the case with her. She informed Summer that he needed to conduct a Mobley family history to determine if there was a prevalence of violent behavior that might suggest a genetic predisposition. Summer then spoke with Joyce Ann Elders, Mobley’s father's cousin, who was considered the family historian. She revealed to Summer that a number of people in the last three generations of the Mobley family had exhibited aggressive and antisocial behavior. These people included a murderer, a rapist, an armed robber, several substance abusers, and several spouse abusers.

Summer then contacted the National Psycho Pharmacology Lab and a doctor at the Emory Nuclear Medicine Laboratory about the cost of preliminary testing to determine if Mobley had the same gene mutation as the people in the Netherlands study.  Summer filed a “Motion for Continuance and Motion to Provide Funds for Expert Witness Assistance to Conduct Preliminary Analysis for MAOA Deficiency and other Genetic Analysis as Information Becomes Available” and supported the motion with his research, affidavits from doctors, and testimony from the family historian. After a hearing, the trial court denied Mobley funds to hire a geneticist and funds to conduct the genetic testing because the Netherlands family had a prevalence of mental retardation and Mobley’s family did not. Mobley’s father offered to pay for the genetic testing himself, but Summer declined. The habeas court has ruled that trial counsel was ineffective for failing to accept Mobley’s father’s offer to pay for the genetic test.

“The evidence shows that trial counsel decided against going forward with the genetic test because (1) they believed that there was only a slim chance that the genetic test would reveal that Mobley had the same genetic defect as the people in the Netherlands study, (2) they intended to present a genetic defense without the geneticist, by using the family historian, and (3) they believed that the trial court's denial of funds might constitute reversible error and they wanted to preserve the issue for appeal. The first two reasons for declining the father's offer were reasonable conclusions. Trial counsel’s desire to “preserve” the issue for appeal, however, was not a reasonable basis for the decision. We do not condone trial counsel foregoing a vigorous defense in the hope that a ruling might constitute error on appeal. If Mobley had prevailed on this issue on appeal, the reversal of the trial court would only result in a new trial in which counsel would have the assistance of a genetics expert, which is the same relief Mobley’s father offered in the beginning.

“Nevertheless, we conclude that the decision regarding the genetic test was a reasonable strategic decision and therefore did not constitute ineffectiveness by trial counsel. The presence of one flawed reason does not render counsel's otherwise reasonable strategic decision deficient performance. Additionally, Mobley was able to present the genetics theory and there has been no showing that a geneticist would have offered additional significant evidence. Therefore, even if the decision constituted deficient performance, Mobley has not demonstrated prejudice.

“D. The mitigation defense.

“The habeas court ruled that trial counsel presented an inadequate mitigation defense. Specifically, the habeas court found that, after being denied the funds for a geneticist, Mobley’s counsel nonetheless persisted with presenting an unconventional genetic theory for Mobley’s behavior, without the assistance of an expert witness. We disagree because this ruling fails to take into account the fact that the genetic defense was only one part of trial counsel's overall mitigation strategy.

“Mobley’s counsel's strategy in the penalty phase centered around the following theme: Mobley has a personality disorder that has affected his behavior since he was a child, this behavior may be the result of a genetic problem that he cannot control, the jury should show him mercy because people with personality disorders tend to “mellow out” as they age, and Mobley has accepted responsibility for his crimes by cooperating with the police and offering to plead guilty. Trial counsel adequately prepared the witnesses for their testimony and called Mobley?s father as the first mitigation witness. He testified about Mobley's childhood problems and all the schools and juvenile institutions that Mobley had attended. He stated that a doctor had told him that his son would “mellow out” by age 40, and he also pleaded with the jury to spare his son's life. The next witness was Dr. J. Steven Ziegler, who had evaluated Mobley when he was almost seventeen years old. Dr. Ziegler testified that Mobley had a conduct disorder that would develop into a personality disorder and that a person who has this disorder displays antisocial personality characteristics. Dr. Ziegler further testified that people with conduct or personality disorders tend to display fewer problems as they age, and that there were some experimental drugs that had shown promise in treating people like Mobley. Next, Summer himself testified that Mobley had been willing to accept responsibility for his actions by pleading guilty and accepting the maximum years for each crime.  The following witness was another lawyer, who testified that it would have been unprofessional for Summer to plead Mobley guilty without some type of assurance that death would not be imposed. Lastly, Joyce Ann Childers testified about the prevalence of people with criminal or behavioral problems in the last three Mobley family generations. She also testified that these people had tended to exhibit fewer aggressive tendencies (“mellow out”) as they reached middle age. In his closing argument, Summer argued that Mobley's personality disorder had a genetic basis, that the jury should not sentence him to death for a disorder that may lessen with age, and that medical technology may be able to treat in the future.”

(4) Neurons.  The basic unit of structure and function in the nervous system and brain is the neuron, a specialized, excitable, cell capable of conducting electrical signals.  A neuron has three basic parts: (1) cell body or soma; (2) dendrite; and (3) axon.  The dendrites and axons are long processes that extend from the cell body which, like electrical cables, conduct electrical impulses towards and away, respectively, from the cell body.

The nervous system communicates by electrical signals.  Its functionality and operation relies on the flow of these electrical signals through a chain of neurons distributed throughout the body, connecting the brain to the motor and sensory organs.  The neurons which comprise the chain are not in physical contact with each other, but are separated by a minute space called a “synapse.”  Typically, an axon from one neuron will form a synapse with the dendrite or cell body of a neighboring neuron.   An electrical signal is propagated through the synaptic space.  A signal moves along the dendrite, through the cell body, and then out along the axon.  When the signal arrives at the tip of the axon, it causes the release of specific chemical molecules called “neurotransmitters.”  There are more than a dozen different neurotransmitters; cells normally produce only one or two kinds.  The neurotransmitter, when released from the axon, diffuses across the short, synaptic cleft.  At the other side, is the dendrite or cell body of another neuron containing special proteins, called “neurotransmitter receptors,” which receive the neurotransmitter like a key fitting into a lock.  Attachment or “binding” of a neurotransmitter to its cognate receptor initiates an electrical signal which, in turn, travels down the dendrite, into the soma, and out the axon.  This successive chain of events underlies almost all sensory and motor functions.

Neurotransmitters and their receptors are important targets in the treatment of mental conditions and diseases.  Schizophrenia is believed to be a defect in the dopaminergic system.  Many anti-schizophrenic drugs operate by blocking the action of dopamine at the dopamine receptor.  Such blocking drugs are referred to as dopamine antagonists because they bind to the dopamine receptor without stimulating it.  Another target for mental disease are enzymes involved in neurotransmitter synthesis.  Monoamine oxidase (“MAO”) is an enzyme in the synthetic pathway for the neurotransmitters, epinephrine and serotonin.  Nardil, is a MAO inhibitor used to treat depression and anxiety.  By inhibiting MAO, synthesis of the neurotransmitter is decreased, presumably depressing neuronal activity.  There are many strategies for pharmacologically modulating synapses.  Fluoxetine, sold under the tradename “Prozac,” blocks the re-absorption of serotonin from the synapse, apparently prolonging the stimulatory effect of serotonin.  Prozac is commonly prescribed for depression.

(5) The XYY myth. In the 1960’s, several studies identified an increased frequency of men with the XYY genotype in prison populations.  These observations led to the hypothesis that the extra Y chromosome caused aggressive and violent behavior.  See, e.g., Jacobs, 1965; Hook, 1973.  The association between the XYY genotype and antisocial behavior has been hotly debated.  A comprehensive study in 1976 of males born between 1944 and 1947 in Denmark found no support for the hypothesis.  Witkins et al., Science, 193: 547-555, 1976.  Instead, they found that in the general population XYY men did not differ from genotypically normal XY men in violent or criminal behavior.  However, they were more likely to be taller than their normal counterparts. These, and other studies, have also shown that XYY men scored significantly and substantially lower on intelligence tests than normal XY men.  Schiavi et al., Arch. Gen. Psychiatry, 41:93?99, 1984.

(6) The legislature of the State of New Biology passes a statute requiring genetic testing of 4-6 week old fetuses for a list of 100 disease genes, including cystic fibrosis, Duchenne’s Muscular Dystrophy, and Down’s syndrome, 20 genes involved in the predisposition to cancer, and 25 genes involved in increasing propensity to schizophrenia, aggression, anxiety, and neurosis.  Abortion is required if one or more such identified genes are found present in the fetus.  According to the legislative history, the purpose of the statute is to protect the community as a whole from disease, and to conserve economic resources by eliminating the high costs associated with chronic disease.  Is this a valid exercise of the state’s police power?