Humans evolving for violence: Genetics and culture

Human_violenceAround the world, humans are exhibiting a great capacity for compassion and social progress, as well as an equally grand tendency for cruelty. With advancements in material culture, our struggles for survival have become exceedingly more complex and unified and violent. According to the Geneva Declaration on Armed Violence and Development (Geneva Declaration Secretariat 2011), a Switzerland-based diplomatic initiative that identifies interrelations between global violence and development, more than 526,000 people die violently each year, of which 396,000 are the result of intentional homicides. One-quarter of those deaths occurred in only 14 countries, where average annual violent death rates exceed 30 per 100,000. Armed violence in non-conflict countries is sometimes more dangerous than combat zones. According to the Geneva Declaration (2011), while U.S.-led coalition troops fought in Iraq between 2004 and 2009, more people per capita were killed in El Salvador. The United Nations (2011) reports some countries have revealed decreased homicide rates in the past 15 years – mainly in Asia, Europe and North America – but their data also shows increases in others (p. 9). Central America and the Caribbean are nearing a “crisis point” (p. 10). Humankind’s constant, sometimes alarming, fluctuations in community homicides has resulted in scientific hypotheses concerning clashes between internal and external environments. Recent research suggests our DNA holds instructions for reacting violently to environmental stress.

Eisner (2003), professor of comparative and developmental criminology at Cambridge University, United Kingdom, said research into criminal behaviors between the 13th and 20th century reveals a 15th century climax in homicide rates in Europe, followed by a rapid decline (p. 99). The peak in violence occurred after an era of crisis and chaos. Trading between Western and Eastern Europe was disturbed with the Ottoman Turks’ takeover of Constantinople, the heart of the Eastern Roman Empire (Kessler Associates 2011). The final battles of a series of regional conflicts, known as the “Hundred Years War,” ended with French victories and English retreats (Keen 2011). In the aftermath, community tribulations collided with the devastating Black Death. The plague peaked in the 14th century, sweeping through Europe and killing about a third of the population, but its horrors continued to linger during the 15th century (Ibeji 2011). Aggressive interpersonal disputes often led to manslaughter or murder. Eventually, Europe’s dark and dreary Middle Ages gave way to an exciting Renaissance, marked by advances in science, architecture, infrastructure and technology, as well as celebrations in art, music and theater. Europe’s homicide rate plummeted – today it’s roughly half the global average (United Nations 2011).

Crusaders_drive_into_constantinopleEisner (2011) conducted a scientific review of research that explored the causes of human violence and identified six central themes in the literature: the prehistory of violence; history and evolutionary theory; morality and compliance in state societies; violence and power; cooperation and retaliatory violence; and the biological underpinnings of violence. According to Eisner, “historians of violence were hardly aware of biological or neurological research on human aggression, while very few criminologists ventured into history or prehistory to gain a fuller understanding of problems in contemporary societies” (p. 473). Eisner commends social historian Roth, professor in the departments of history and sociology at The Ohio State University, for drafting “a fascinating framework to integrate evolutionary and biological scholarship into an explanation of the variability of violence across time and space” (p 476). Drawing on Roth’s extensive research, spanning 450 years in the United States and Europe, Eisner agrees on evading the question of whether genes or culture drive violent behaviors. Instead, both factors may be intricately intertwined in producing behavioral changes. Roth encourages the scientific community to expand its understandings of the biological traits that support trust and cooperation under stable conditions, and anger, retaliation and aggression during low political stability (p. 477).

Roth (2011) suggests human neural and endocrine systems may have “evolved” for homicidal behaviors (p. 535). Environmental stressors caused by unstable habitats may have triggered rapid genetic adaptations in Homo Sapiens, including those favoring the nurture or neglect of children, or cooperation or aggression among unrelated adults. Humans have revealed an amazing adaptive ability since emerging on Earth more than 3 million years ago. About one million years later, the first hominid exhibiting anatomical and behavioral characteristics similar to modern humans arrived. According to Larsen (2011), professor in social and behavioral science at The Ohio State University, fossil evidence suggests changes in early human body sizes occurred rapidly and in succession to changes in environments, including climates and resources. The earliest evolution of archaic Homo Sapiens began 350,000 years ago, and the most modern version is 160,000 years old. The human species has quickly ascended as skilled hunters and communicators capable of advanced tools and intellect.

In 1831, soon after graduating Cambridge University with training in medicine and theology, Charles Darwin was appointed the naturalist for a five-year voyage around the world, where he collected data that “would provide the key to understanding the origin and evolution of life itself,” according to Larsen (p. 25). In his historic report “On the Origin of Species,” Darwin (1859) states that “natural selection will never produce in a being anything injurious to itself, for natural selection acts solely by and for the good of each … if a fair balance be struck between good and evil caused by each part, each will be found on the whole advantageous” (p. 179). Darwin’s theories of natural section, where certain biologic traits become either more or less common, offer evidence that aggression is advantageous to humans.

Nonhuman primates have provided advanced understandings of blood chemistry changes in a variety of social settings. Roth (2011) notes that “under unstable conditions, serotonin levels decrease in group-living monkeys and apes in anticipation of aggression” (p. 545). Their suddenly low levels of serotonin encourage impulsive actions and sudden, uncontrolled aggression. Experiments with rhesus monkeys also demonstrated that relatively low levels of serotonin forecasts aggression. Moreover, lowering serotonin levels in troops of vervet monkeys dramatically increases spontaneous acts of aggression.

Recent evidence of a gene-environment interaction is underscoring the role of individual human variances in expressing aggression. McDermott, Tingley, Cowden, Frazzetto, and Johnson (2009) point to a part of human DNA that has earned the monicker “warrior gene.” This gene codes for the enzyme monoamine oxidase A (MAOA), which plays a key role in the breakdown of neurotransmitters, including serotonin. The researchers tested whether the warrior gene genotypes promoted aggressive tendencies in people. They conducted a four-round “power-to-take” game with human subjects that used psychology and behavioral economics. Aggression was measured through subject-determined levels of hot sauce administration. They found evidence that MAOA significantly predicts aggression in a high provocation situations, more so than low conditions. The genotypes were eager to harm others who hurt them or their group. Furthermore, the subjects proved willing to allow a personal financial cost to physically punish others. While the warrior gene is costly to its host and community, the genetic trait seemingly empowers a person to fight adversity.

While the warrior gene is costly to its host and community, the genetic trait seemingly empowers a person to fight adversity.

Roth (2010) suggests low homicide rates have occurred in the United States when there’s trust in the government, supported by “a belief that government is stable and that its legal institutions will protect lives and property; patriotism, empathy, and fellow feeling arising from racial, religious, or political solidarity; and the belief that the social hierarchy is legitimate and enables men to attain a satisfactory position in society and to command the respect of others without resorting to violence” (p. 185). Roth explains that the homicide rate in U.S. cities fell 14.5 percent between November 2008 and February 2009, after the election of the first black president. Citing a poll in 2009, he said, “blacks were more optimistic about the nation’s future and their place within it than they had been in a generation, despite two wars and a recession” (p. 187). Eisner (2011) agrees that historical flfluctuations in homicide rates have been influenced by public perceptions: “legitimacy of overarching political institutions, fair and effective police and courts, a trust in the government, a sense of community and an accepted mode of allocating resources” (p. 476-477). While the Geneva Declaration (2011) found a strong association between tough law enforcement activities and low homicide rates, even those heavily policed societies breakdown when communities remain troubled by gang activity, past conflicts and high income inequality. People must believe justice will prevail.

U.S. citizens are complaining of financial and political problems. In 2010, median household income in the United States declined and the official poverty rate increased to 15.1 percent, up from 14.3 percent in 2009 – the third consecutive annual increase (U.S. Census Bureau 2011). The economic turmoil mounted amid consumer price inflation, elevated unemployment numbers, plummeting home values and dwindling pension funds. “Occupy Wall Street” protestors in more than 100 U.S. cities are calling out major banks and multinational corporations for their corrosive power over democratic processes ( 2011), while a “Tea Party” movement is rallying against fiscally irresponsible actions of the federal government (Tea Party Patriots Inc. 2011). Recent ratings of the U.S. public’s perception of Congress are among the worst in the more than 30-year history of Gallup’s Honesty and Ethics Survey (Jones 2010). The United States appears aptly charged for violent outbreaks.

The United Nations (2011) reports that homicide rates in the United States are relatively high, as compared to other countries of a similar socio-economic level. Nonetheless, the rates have declined to the lowest levels in nearly 50 years, according to the U.S. Bureau of Justice Statistics (Cooper & Smith, 2011). The dropping rates occurring during widespread perceptions of poor governance and inadequate income dispersions conflicts with the innate biological responses expected by researchers like Eisner and Roth. However, the concurrent decline may represent a technical glitch, since innovations have boosted crime prevention efforts. For example, the widespread proliferation of mobile telecommunication technologies, equipped with high-definition imagery and global positioning system capabilities, are allowing great accuracy in recording and reporting criminal activity. Americans are getting convicted for crimes at an alarming rate. The U.S. Census 2010 showed the country’s population increased about 36 percent in the past 30 years (2011). Meanwhile, the Bureau of Justice Statistics (2011) recorded prison and jail populations surging an astonishing 355 percent during the same period. Today, for every 135 citizens, roughly one person is incarcerated – those Americans may represent a significant portion of the U.S. population that’s afflicted by biological tendencies for aggression, such as the warrior gene.

World peace depends on understanding how violent conflict is perpetuated, according to Pilisuk and Zazzi (2006), who suggest global violence reflects “increasing concentrations of wealth and power among a few dominant players to the exclusion of others” (p. 42). They hypothesize that violence is caused by mounting cultural beliefs that serve to benefit an elite network that hoards wealth, limits democratic participation and justifies armed conflict as national interest.

They hypothesize that violence is caused by mounting cultural beliefs that serve to benefit an elite network that hoards wealth, limits democratic participation and justifies armed conflict as national interest.

Religious fundamentalists are well known for expressing cruelty, arguable the most notable is the Taliban, a group of Islamic extremists operating in the foothills of Afghanistan. For example, rural families that are shamed by a daughter may carry out a so-called honor killing (Baker 2010). The Afghans are primed to express warrior genes within their people, many of which are suffering from political instability and unstable resources. Transparency International (2011), a Berlin-based global network that measures corruption, rates Afghanistan as the world’s fourth most politically corrupt nation, behind Myanmar, North Korea and Somalia, respectively. According to the CIA, the per capita gross domestic product is a dismal $900 and the unemployment rate is 35 percent (2011). Pilisuk and Zazzi warn that “the pursuit of economic interests through suppression of dissent, displacement and killing” can cause a “cycle of violence” (p. 51). As noted in the warrior gene research, a need for vengeance can overcome people.

During U.S.-led attacks on Islamic extremists in Afghanistan, the Taliban started killing police officers, government officials and village elders working with the foreign forces. According to a former Taliban deputy minister who became an insurgent recruiter, U.S. operations that harassed villagers and attacks that killed civilians, combined with Afghan government corruption, alienated villagers and made them Taliban sympathizers – “soon we didn’t have to hide so much on our raids,” he said. “We came openly. When they saw us, villagers started preparing green tea and food for us” (Yousafzai & Moreau 2009). Afghanistan’s latest hope rests in a new vein of resources. In 2010, the United States discovered nearly $1 trillion in untapped mineral deposits there, “far beyond any previously known reserves and enough to fundamentally alter the Afghan economy and perhaps the Afghan war itself,” according to senior U.S. government officials (Risen 2010). The deposits include iron, copper, cobalt, gold and lithium; each essential to modern industry and capable of transforming Afghanistan into one of the most important mining centers.

When national wealth is aptly distributed and corruption is effectively curbed, biological traits favoring violence are suppressed, according to current research exploring genetic links to aggression. Scientists have put forward evidence that some human genotypes pass on instructions for violence. However, the behavioral trait is reserved for highly-provoked situations, as an innate reaction favorable to survival. The source of human violence may rest below the boundaries of religious fundamentalism, public policies or other systems outlining social order. The roots appear tied to the breakdown of perceptions concerning community instability, unjust authority and an unfair diffusion of resources.

Works Cited

Baker, A. (2010, August 9). Afghan women and the return of the Taliban. Retrieved December 1, 2011, from Time:,9171,2007407,00.html

Bureau of Justice Statistics. (2011, December 1). Correctional populations. Retrieved December 1, 2011, from Bureau of Justice Statistics:

Central Intelligence Agency. (2011). Afghanistan. Retrieved December 1, 2011, from World Factbook:

Cooper, A., & Smith, E. (2011, November 16). Homicide trends in the United States, 1980-2008. Retrieved December 1, 2011, from Bureau of Justice Statistics:

Darwin, C. (1859). On the origin of species by means of natural selection or the preservation of favored races in the struggle for life. London: John Murray.

Eisner, M. (2011). Human evolution, history and violence: An introduction. British Journal of Criminology , 51 (3), 473-478.

Eisner, M. (2003). Long-term historical trends in violent crime. Crime & Justice , 30, 83-142.

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Ibeji, M. (2011, March 10). The plague. Retrieved December 1, 2011, from BBC:

Jones, J. (2010, December 3). Nurses top honesty and ethics list for 11th year. Retrieved December 1, 2011, from Gallup:

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Larsen, C. (2011). Our Origins: Discovering physical anthropology (2nd ed.). New York: W. W. Norton & Company, Inc.

McDermott, R., Tingley, D., Cowden, J., Frazzetto, G., & Johnson, D. (2009). Monoamine oxidase A gene (MAOA) predicts behavioral aggression following provocation. Proceedings of the National Academy of Sciences , 106 (7), 2118-2123. (2011). About. Retrieved December 1, 2011, from

Pilisuk, M., & Zazzi, J. (2006). Toward a psychosocial theory of military and economic violence in the era of globalization. Journal of Social Issues , 62 (1), 41-62.

Risen, J. (2010, June 13). U.S. identifies vast mineral riches in Afghanistan. Retrieved December 1, 2011, from The New York Times Company:

Roth, R. (2010). American homicide: Theories, methods, and body counts. Historical Methods , 43 (4), 185-192.

Roth, R. (2011). Biology and the deep history of homicide. British Journal of Criminology , 51 (3), 535-555.

Tea Party Patriots, Inc. (2011). About Tea Party patriots. Retrieved December 1, 2011, from Tea Party Patriots:

Transparency International. (2011). Corruption Perceptions Index 2011 results. Retrieved December 1, 2011, from Transparency International:

U.S. Census 2010. (2011). Population density. Retrieved December 1, 2011, from U.S. Census 2010:

U.S. Census Bureau. (2011, September 13). Income, poverty and health insurance coverage in the United States: 2010. Retrieved December 1, 2011, from U.S. Census Bureau:

United Nations. (2011). 2011 Global study on homicide. Retrieved November 27, 2011, from United Nations Office on Drugs and Crime:

Yousafzai, S., & Moreau, R. (2009, October 5). The Taliban in their own words. Newsweek , 154 (14).

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