Are We Programmed to Be Violent? (Adobe Stock) 1050 × 788

That the human species is violent needs no elaborate scientific study—just turn on your TV set on any given day and you’ll see it in its full gory glory. These days, it’s the relentless bombing in Aleppo. In 1995, it was the massacre of Srebrenica. A year earlier, it was Rwanda’s turn. And, of course, who could deny the enormity of the Holocaust during WWII, 1939-1945.

 

Is this a modern phenomenon?

Evidence of systematic violence dates back to the stone age. The first farmers arrived in central Europe from Anatolia around 7,500 years ago. Archaeologists and anthropologists had a pet theory that farming made these early Europeans peace-loving people. They were more interested in raising crops, domesticating animals, decorating their ceramics, and raising their families. But then came a spectacular discovery and a rude awakening.

In the 1980s, the discovery of two Neolithic mass graves in Germany and Austria led many archaeologists to discount peaceful accounts of these early European farmers. The graves contained more than 100 bodies that bore the marks of a violent attack. Considering how low the population density was in stone-age Europe, this could qualify as a massive massacre. Other researchers, however, continued to hold that violence among Neolithic people was rare, and they dismissed these massacre sites as peculiarities.

Now, however, a newly discovered mass grave in Germany makes the task of deniers of prehistorical systematic violence much more difficult. The first farmers were far from peaceful tillers of the soil—the people in the 7,000 years old mass grave show signs of severe injuries, many of them with smashed skulls and broken legs. Neolithic graves normally contain goods to accompany the departed on their journey. The mass grave doesn’t contain any grave goods. Nor does it show any sign of care or ritual given to the bodies before they were buried. This evidence supports the idea that the grave holds massacre victims.

 

Is violence hard-wired in our DNA?

The fact that planned massacres, as opposed to random violence, dates to the prehistory makes one wonder if this trait is hard-wired in our DNA. That’s a tough question to investigate by simply examining ancient human genomes. The trait of violence is most likely not monogenic, but a result of multiple gene interactions. And, cultural influences are bound to further muddy the picture. For instance, the 3 mass graves discovered thus far in Germany are linked to the Linearbandkeramik (Linear Band Ceramic, or LBK) culture, a group named for the linear ornaments on their pottery. The LBK originally came from the Middle East and brought sheep, goats, and other domesticated animals with them as they began setting up farms and small villages in central Europe. Which begs the age-old question of Nature vs. Nurture: Was there anything in the culture or economic conditions of those early Germans that predisposed them to violent warfare, or are humans genetically predetermined to be prone to violence?

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A new study published in Nature makes a compelling case that violence is embedded deep in our lineage. And I mean really deep—all the way back to marsupials and tree shrews, which made their entrance in evolution about 200 million years ago, living side by side with the dinosaurs. Our species, H. sapiens, appeared only 200,000 years ago. Obviously, then, any trait shared with mammalian species that preceded us can be assumed to be genetically determined. How can we make such an assumption? It is based on none other than Darwin and his insights.

In his book, The Descent of Man, Charles Darwin observed that one species evolves from another by undergoing modifications (mutations), but that the daughter species still retains many of its ancestors’ traits. This is why we and the remotely related species that preceded us by millions of years, such as the lizards, share the same genes that control vital functions for survival, for instance, the ‘fight-or-flight’ response.

Indeed, comparative biologists use the family trees (phylogenies) that arise from the process of speciation (one species evolving from another) to infer the history of biological evolution, to date past events, and to reconstruct probable ancestral features of species that lived hundreds of thousands to hundreds of millions of years ago. And that’s what the investigators did. They compiled information on more than 4 million deaths from 1,024 mammal species drawn from 137 mammalian families (80% of the total number of mammalian families), including mice, horses, bats, rabbits, and monkeys. Information for humans came from 600 studies, and was derived from paleolithic samples (defined by the authors as 50,000 to 12,000 years ago), New World and Old World Mesolithic (12,000 to 10,200 years ago) and Neolithic (10,200 to 5,000 years ago) sites, Bronze Age (5,300 to 3,200 years ago) and Iron Age (3,200 to 1,300 years ago) samples, and anthropological sources from the past few centuries. From this extensive database, they calculated the proportion of deaths attributable to violence from a member of the same species out of all deaths counted for each species. Including only acts of within-species violence is a key point; a hunter, be it an animal or a human, is killing to eat. But killing a fellow human being, or a gorilla killing a member of a different band to protect his territory or his supremacy within his band, is different; it is lethal violence.

What the data showed is that in early mammals, like marsupials and grazing animals, the rate of lethal violence is 0.3% (1 in 300). This rate constantly climbs as we progress through the evolutionary tree, reaching 1.8% in the great apes. Considering that we share 98% of our genes with gorillas, one would expect our rate of lethal violence to be close to that of apes. Indeed, the incidence of human lethal violence at the origin of our species (150,000 – 200,000 years ago) is calculated at 2%. But then rates rise to as high as 15–30% (with high statistical uncertainty) in samples from between 3,000 and 500 years ago, before declining in contemporary populations (approximately 100 years ago to the present day). The rise tends to correlate with moving from an early pre-societal ‘state of nature’ to tribal groupings and then to organized political societies that have a warrior class.

 

Are we doomed to eternal violence?

Not quite. Societies have evolved—and some are still evolving—into a ‘rule of law’ society. Rates of homicide in modern societies that have police forces, legal systems, prisons, and strong cultural attitudes that reject violence are, at less than 1 in 10,000 deaths (or 0.01%), about 200 times lower than the authors’ 2% finding for our ‘state of nature’.

So let’s face it, violence is deeply rooted in our genes. The good news is that we have the tools to overcome our genetic imperative—societal order, morals, ethics, and, if all fails, police and a judicial system. In fact, studies show that the prime motivator for obeying the laws of an orderly society is not all those wonderful “values” of a liberal society—it is fear itself.

Who would have guessed that one of our most primitive reflexes, fear, is actually important in the development our modern, law-abiding societies? And that in the context of human evolution, the murderous outbursts we are witnessing today are just an aberration. A surprising and hopeful insight, to be sure.



Dov Michaeli, MD, PhD
Dov Michaeli, MD, PhD loves to write about the brain and human behavior as well as translate complicated basic science concepts into entertainment for the rest of us. He was a professor at the University of California San Francisco before leaving to enter the world of biotech. He served as the Chief Medical Officer of biotech companies, including Aphton Corporation. He also founded and served as the CEO of Madah Medica, an early stage biotech company developing products to improve post-surgical pain control. He is now retired and enjoys working out, following the stock market, travelling the world, and, of course, writing for TDWI.

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