Heritability of Aggression: Genes, Environment, and Violence

Introduction

There is a social bias against the idea of aggression, such that many people conflate aggression with violence and cannot separate the two concepts. This conflation implies that aggression is inherently negative, which is not necessarily the case. Suggestions that aggression is somehow genetic have consequently been distorted into the notion that people carrying those genes must be inferior to the rest of the population. This is untrue on several levels. First, it assumes that aggression must be negative. Second, it assumes that acting on aggressive behavior must be maladaptive. Neither assumption is warranted, yet both highlight the pitfalls involved in examining aggression.

Examining whether aggression can be inherited is a morally risky endeavor. It cannot be ignored that prior attempts to link genetics and antisocial behavior — including aggression — have been used to reinforce racial stereotypes, to justify prejudiced behavior, and to enact discriminatory policies. However, it also cannot be ignored that, while linking heritability with aggression carries potentially negative social and policy consequences, there does appear to be some evidence that aspects of antisocial behavior, including aggression, may have a genetic basis. If that is the case, then it seems important to understand the nature and extent of the heritability of aggression, so that naturally occurring aggression can be limited or channeled without penalizing people for an inherited predisposition toward greater violence than average.

Scientists appear willing to revisit the idea that aggression may have an inherited component. As one observer noted, "the tainted history of using biology to explain criminal behavior has pushed criminologists to reject or ignore genetics and concentrate on social causes: miserable poverty, corrosive addictions, and guns. Now that the human genome has been sequenced, and scientists are studying the genetics of areas as varied as alcoholism and party affiliation, criminologists are cautiously returning to the subject" (Cohen, 2011). However, it is important that any results be viewed with caution, given the way hereditary links to violence or aggression have been used to discriminate against groups of people. It is critical to keep in mind that "genes are ruled by the environment, which can either mute or aggravate violent impulses. Many people with the same genetic tendency for aggressiveness will never throw a punch, while others without it could be career criminals" (Cohen, 2011). Therefore, it is important to consider how environmental factors mediate and interact with genetic factors.

Historical Background: Eugenics and Hereditary Research

Studying the possible genetic influence on aggression began in earnest in the late twentieth century and transformed from a scientific goal into a social movement. "Francis Galton, who coined the term eugenics in 1883, perceived it as a moral philosophy to improve humanity by encouraging the ablest and healthiest people to have more children" (Carlson, n.d.). However, the positive view of eugenics did not last. Instead, many people began to focus on negative eugenics, which held that some people should not reproduce because of their faulty genes. This led to atrocities in many countries that subscribed to the theory that negative traits were inherited — including forced sterilizations in the United States. Eugenics also played a significant role in the rise of the Nazi party in Germany, which advanced the idea that Jewish people were genetically inferior. Only after Nazi atrocities began to receive widespread negative publicity did people in the United States and the rest of Europe begin to distance themselves from negative eugenics, including from research into hereditary aspects of aggression.

Even as it became increasingly unpopular to suggest that antisocial behaviors such as aggression had a genetic component, evidence continued to accumulate suggesting there was some hereditary basis. Research began to support the anecdotal observation that "aggression and antisocial behavior run in families" (Miles & Carey, 1997). Not all studies looked specifically at aggression. Instead, aggression was measured through a variety of proxies: delinquency, criminality, conduct disorders, and antisocial personality (Miles & Carey, 1997). However, the finding that such behaviors run in families is not the same as finding that they are genetic. "Although similarity among family members for aggressive or antisocial behavior has been evident, the study of intact nuclear families has not been able to trace this similarity to shared genetic influences, shared familial environmental factors, or some combination of both genes and environment" (Miles & Carey, 1997). Early researchers therefore turned to twin studies and comparisons of adopted children with their biological parents. These studies supported the idea that aggression has a hereditary component, while also making clear that the genetic component plays only a partial role in predicting whether someone will be aggressive.

In order to fully understand what it means to investigate the heritability of aggression, it is important to understand what researchers mean by the term. In the context of studies examining aggression and heredity, aggression appears to be linked to anger and its negative consequences. Depending on the researcher, aggression may be used interchangeably with propensity for violence, criminality, antisocial behavior, and even an inability to concentrate. In fact, aggression often seems interchangeable with the concept of anger and the capacity to control angry impulses. "Aggression has been defined as behavior produced to cause physical harm or humiliation to another person who wishes to avoid it (Baron & Richardson, 1994). Although this definition is functional, it does reflect a potential bias in assuming that aggression is inherently bad" — the definition implies that the aggressor is a "perpetrator" and the recipient is a "victim," making it an incomplete account of aggression (Ferguson & Beaver, 2009).

Defining Aggression and Its Dimensions

It is also important to distinguish aggression from violence. If violence is understood as the nonconsensual use of force or power against another person, then almost all violent behavior would be aggressive, though some may question whether violence in self-defense qualifies as either violent or aggressive. Moreover, while "violent behavior certainly would be aggressive, but not all aggressive behaviors are violent or even necessarily negative from a cultural perspective" (Ferguson & Beaver, 2009). Instead, aggression functions on a continuum — a continuum not always captured in research on the subject.

What historical approaches have often failed to consider is that aggression is not a wholly negative adaptation. From an evolutionary standpoint, more aggressive individuals would have been more likely to survive and prosper in competitive environments, because greater aggression confers advantages in obtaining resources. On the other hand, individuals who were so aggressive as to be expelled from the group were probably less able to successfully pass on their genes. The implication is that, while excessive aggression is undesirable, some degree of aggression is adaptive — and the acceptable level of aggression is context-dependent. What is considered acceptable aggression in battle differs significantly from acceptable behavior in a corporate boardroom. Furthermore, aggression does not necessarily involve violence: "acceptable aggression expressed in judging or subduing others is also a safety valve for discharging remaining pent-up aggression" (Fauteux, 1994).

Research on aggression has focused primarily on those who are considered overly aggressive, and on aggression that has been expressed through observable behavior — treating aggression as a verb. However, aggression is also a noun: a person can experience aggressive feelings and instincts even without acting on them. "We must distinguish between two facets of emotion, the functional and the experiential" (Kosslyn & Koening, 1992). While it is understood that some genes may increase the likelihood of acting on aggressive feelings, it is far less certain whether there are genes that increase the likelihood of feeling those aggressive impulses in the first place. Much of the research focus has instead been on impulse control, and a general trend suggests that those who have difficulty controlling aggressive impulses also tend to be impulsive in other areas of their lives.

Conclusion

In many cases, the predisposition to violence or aggression has already been triggered by the time an individual comes to the attention of those who might wish to intervene — that is, the person may already be incarcerated or otherwise involved in the legal system, and intervention comes too late. This has led some researchers to suggest that screening for genetic markers — for example, screening male victims of childhood abuse for low-activity MAOA alleles — would help society concentrate rehabilitation and counseling efforts on the individuals who need it most, potentially reducing future violence as those individuals grow into adulthood.

In theory, such interventions seem appropriate and beneficial. However, given the gross historical misuse of genetic information to carry out racist and sexist programs, any policy that would single out individuals for different treatment on the basis of their genes must be evaluated with extreme caution. The science of heritability and aggression holds genuine promise, but only if pursued with a firm commitment to ethical responsibility and an awareness of the harms that have followed when that responsibility was abandoned.