Did humans and chimps inherit a violent nature from a common ancestor?

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Why are we violent?

There's no denying that humans are violent creatures. From domestic violence within the home to globe-spanning wars, humans have a habit of acting on aggression. Where does this violent behavior come from? Are we hardwired with it, or do we learn this behavior? And is there any way to move beyond being a violent creature?

If you take a good look at the animal kingdom, you'll notice only a few species enact violence upon each other the way humans do. Most animals use aggressive displays to ward off competitors for food or mates without the intention of causing serious injury or death. Predators kill primarily for sustenance -- preying upon species other than their own. Two notable exceptions to this general rule are humans and chimpanzees [source: Wrangham and Peterson].

Like early humans, chimpanzees form small groups in which individuals depend upon one another. Chimps from one group may leave and join another or form their own. And chimps that grew up playing together may one day face each other in a fight to the death.

Scientists have observed chimps forming raiding parties along the borders of their own territories. A group of male chimps will patrol, searching for members of neighboring groups. If they find one, they may attack with violent ferocity, injuring or even killing their victim. Interestingly, in chimpanzee society, the males are usually the violent gender. The same is true in human society -- studies show men are involved in more violent crimes than women.

Interestingly, the chimpanzee is the animal most closely related to the human. Humans and chimps descended from a common ancestor around five million years ago [source: Wrangham and Peterson]. Is it possible our violent nature comes from this mysterious ancestor? And why would chimpanzees and humans display this sort of behavior when other primates don't?

The truth is that we don't have all the answers. Evolutionary psychologists might say that our prehistoric ancestors passed down a tendency toward violent behavior, particularly among males. But even if this is true, the full explanation is far more complicated. While violence may be part of our genetic history, so is contemplation.

Next, we'll look at the old nature-versus-nurture discussion and how we're really a product of both.

Humans engage in violence ranging from one-on-one confrontations to global conflicts.

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Nature, Nurture and Violence

To say violence is part of our evolutionary process is an oversimplification. Not everyone exhibits violent behavior. If humans were naturally and chaotically violent, our species wouldn't have survived for millennia.

But if we dig down, we'll find even more confusing questions. Are our violent natures buried deep within us, waiting for the right set of circumstances to come to the surface? Or do we need to learn violent behaviors from others? Do our social groups restrict our violent tendencies, or do they foster them?

Psychologists, sociologists, anthropologists and ethologists -- scientists who study behaviors -- struggle to answer these questions. We're complex creatures and there are no easy explanations. We're capable of considering our own actions. Humans can plan and reflect upon our deeds. We're able to question our own motives and consider the consequences of the things we do.

While we may all have the capacity to be violent, we may only exercise violence under certain circumstances. It's not hard to imagine two scenarios featuring the same group of people that result in either repressing violent tendencies or embracing them. In the first scenario, one of the community's defining characteristics is a stable family structure. In the second scenario, the families within the community lack stability. You'd probably guess that the second scenario would be more chaotic and violent. It would be almost impossible and certainly unethical to perform such an experiment. But crime statistics seem to indicate that communities that lack stable family units produce more crime -- particularly violent crime.

Cultural values and beliefs can also play an important role. The Gebusi tribe in lowland New Guinea isn't particularly aggressive -- the men of the tribe don't tend to form raiding parties or militia. Social interaction is marked with affection. But the homicide rate among the Gebusi is one of the highest in the world. One reason is that the Gebusi believe in sorcery and witchcraft -- killing someone believed to be practicing lethal witchcraft is permissible within their culture [source: Knauft].

There are other elements that can influence us to make us violent. Mental disorders or brain damage can affect judgment and perception. These cases are outliers -- they happen, but they're not the common experience among a community.

Within a population, certain traits may make particular subsections more violent. In a study of aggressive behaviors within a college community, researchers discovered that males with low levels of fluctuating asymmetry (FA) admitted to being in fights more than those with high FA. Fluctuating asymmetry is a deviation from perfect bilateral symmetry, and is the product of environmental and developmental stresses. The study suggests males who have greater symmetry -- and presumably fewer mutations than those with less symmetry -- are more violent [source: Furlow, et al.]. In other words, violence may be simply a part of human nature.

Our personalities are the products of thousands of influences. Some are biological and date back to before humans even existed as a species. Others develop as part of our social and cultural practices. We may never have the complete answer to what makes us a violent species. But we should always ask ourselves these questions -- if nothing else, we may find the secret to reducing violent conflict.

For more on violence and other related topics, punch on over to the next page.

Lots More Information

Related ArticlesMore Great LinksSources
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  • Brooks, David. "Human Nature Today." The New York Times. June 25, 2009. (Aug. 26, 2010) http://www.nytimes.com/2009/06/26/opinion/26brooks.html
  • Buss, David M. and Duntley, Joshua D. "Chapter 5: Homicide: An Evolutionary Psychological Perspective and Implications for Public Policy." Evolutionary Psychology and Violence. March 30, 2003. Praeger. Westport, Connecticut. pp. 115 - 128. http://homepage.psy.utexas.edu/homepage/group/busslab/pdffiles/Duntley_Chapter_Evolutionary_Perspective_on_Homicide.pdf
  • Furlow, Bryant et al. "Developmental stability and human violence." The Royal Society. 1998. (Sept. 8, 2010) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1688754/pdf/9470212.pdf
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