In Italy, a judge reduced the sentence of a defendant by 1 year in response to evidence for a genetic predisposition to violence. The best characterized of these genetic differences, those in the monoamine oxidase A (MAOA), were cited as especially relevant. Several months previously in the USA, MAOA data contributed to a jury reducing charges from 1st degree murder (a capital offence) to voluntary manslaughter. Is there a rational basis for this type of use of MAOA (...) evidence in criminal court? This paper will review in context recent work on the MAOA gene–environment interaction in predisposing individuals to violence and address the relevance of such findings to murder trials. Interestingly, the MAOA genetic variants impact future violence and aggression only when combined with the adverse environmental stimuli of childhood maltreatment. Thus nature and nurture interact to determine the individual’s risk. Based on current evidence, I argue there is a weak case for mitigation. But should future experiments confirm the hypothesis that individual differences in impulse control and response to provocation found in MAOA-L men (without abuse) are significantly magnified when combined with childhood maltreatment, the case could turn into a stronger one. (shrink)

The ‘gene of’ is a teleosemantic expression that conveys a simplistic and linear relationship between a gene and a phenotype. Throughout the 20th century, geneticists studied these genes of traits. The studies were often polemical when they concerned human traits: the ‘crime gene’, ‘poverty gene’, ‘IQ gene’, ‘gay gene’ or ‘gene of alcoholism’. Quite recently, a controversy occurred in 2006 in New Zealand that started with the claim that a ‘warrior gene’ exists in the Mãori community. This claim came from (...) a geneticist working on the MAOA gene. This article is interested in the responsibility of that researcher regarding the origin of the controversy. Several errors were made: overestimation of results, abusive use of the ‘gene of’ kind of expression, poor communication with the media and a lack of scientific culture. The issues of the debate were not taken into account sufficiently, either from the political, social, ethical or even the genetic points of view. After more than 100 years of debates around ‘genes of’ all kinds (here, the ‘warrior gene’), geneticists may not hide themselves behind the media when a controversy occurs. Responsibilities have to be assumed. (shrink)

Examining the costs and motivations of warfare is key to conundrums concerning the relevance of this troubling phenomenon to the evolution of social attachment and cooperation, particularly during adolescence and young adulthood—the developmental time period during which many participants are first recruited for warfare. The study focuses on Samburu, a pastoralist society of approximately 200,000 people occupying northern Kenya’s semi-arid and arid lands, asking what role the emotionally sensitized, peer-driven adolescent life stage may have played in the cultural and genetic (...) coevolution of coalitional lethal aggression. Research in small-scale societies provides unparalleled opportunities for sharply defined variables, particularly in age generation societies in which all young men are initiated into “warriorhood.” Proposing an epigenetic and component behavior approach, we examine whether raiding activities such as number of raids, killing, and sparing enemy lives associate with DNA methylation in two candidate genes: MAOA, linked to mood and arousal, and NR3C1, linked to stress and immune response. We report statistically significant associations between the epigenetic variables and the combat variables of overall raiding activity and reportedly showing mercy to enemies. In contrast, epigenetic variables did not associate with post-traumatic stress disorder symptom scores, and the only combat variable associated with PTSD was losing one’s own livestock in a raid. These findings raise important questions concerning the mechanisms driving warfare’s paradoxical mix of violent and altruistic behaviors. (shrink)

Both genetic and environmental factors have key roles in determining aggressive tendencies. In particular, reaction to stress appears to be an important factor in precipitating aggressive episodes and individuals may vary in their ability to cope with stressful environments depending on their genetic make up. Evidence from humans and primates indicates that adverse rearing conditions may interact with variants in stress and neurotransmitter pathway genes leading to antisocial and/or violent behaviour. Common alleles of some serotonin pathway genes, including those involved (...) in its degradation (monoamine oxidase A, MAOA), or its re‐uptake into pre‐synaptic neurones (serotonin transporter, SERT) have been shown to confer functional variation. Examination of the interaction between the alleles of such polymorphisms (in particular those affecting MAOA) and environmental stressors suggest that they may provide protection against, or increase sensitivity to, abusive upbringing; an observation that may explain part of the variability in developmental outcomes associated with maltreatment. BioEssays 29: 227–236, 2007. © 2007 Wiley Periodicals, Inc. (shrink)

Researchers studying human behavioral genetics have made significant scientific progress in enhancing our understanding of the relative contributions of genetics and the environment in observed variations in human behavior. Quickly outpacing the advances in the science are its applications in the criminal justice system. Already, human behavioral genetics research has been introduced in the U.S. criminal justice system, and its use will only become more prevalent. This essay discusses the recent historical use of behavioral genetics in criminal cases, recent advances (...) in two gene variants of particular interest in the criminal law, MAOA and SLC6A4, the recent expert testimony on behalf of criminal defendants with respect to these two gene variants, and the future direction of behavioral genetics evidence in criminal cases. (shrink)