Natural born killers: The genetic origins of extreme violence

a r t i c l e i n f o The current article examines the influence of genetics and evolution on acts of extreme and criminal violence among human primates. Moderate aggression can function to increase an organism's reproductive success; extreme violence can place the organism at unnecessary risk. Genetic polymorphisms that have been linked to extreme acts of violence are reviewed as is research elucidating how genetic risk and environmental stress may interact to increase risk of extreme violence. Extreme violence is viewed as high-end variance in an evolutionarily adaptive process in which the propensity for aggression and violent behavior, in moderate doses, has been adaptive for individual humans. The origin of human violence has been an issue of considerable concern and debate for centuries (e.g., Lombroso, 1876/2006). Violence is just one outcome that has been central to the " nature versus nurture " debate. Given technical limitations and predominating scientific views, much of the research produced on violence during the latter 20th century focused on social, family, and cultural influences on violence. More recent research has indicated that violent behavior has significant biological, genetic, and evolutionary origins as well. Several studies have identified gene polymorphisms that increase the risk for violent behavior. Increasingly, the evolutionary origins of violent behavior are being explored. The current paper seeks to provide a review of what is currently known about the genetic and evolutionary origins of extreme violent behavior. It is important to recognize that the terms used in the current paper, namely " aggression " " violence " and " extreme violence " should not be taken to be synonymous. For instance, when individuals in the general populace learn of research suggesting that, say, " Eating plums increases aggression, " many such individuals may picture children or adults hitting, kicking, fighting, etc., or even imagine that such experimental results extend easily to criminally violent activities. In reality, participants in such studies may be merely filling in the missing letters of words, or delivering non-painful noise bursts to an ostensible consenting reaction-time game opponent (Savage, 2004). Many experimental measures of " aggression " do not predict violent acts or even physically aggressive behaviors As such, a proper understanding of relevant terms and how they are measured is necessary to prevent miscommunication. Aggression has been defined as behavior produced to cause physical harm or humiliation to another person who wishes to avoid …