Are Humans Natural-Born Killers?

Among scientists there has been a long debate about whether human violence toward other humans is inherent, cultural or a mix of both. The question is: Are we natural-born killers, notes Lawrence Davidson.

By Lawrence Davidson

A new study, published in the journal Nature and entitled “The Phylogenetic Roots of Human Lethal Violence,” argues two points: (1) along with many other mammals and particularly primates, human lethal violence is innate because it is part of a long “evolutionary history”; and (2) for humans, however, it is also a behavior that is responsive to our cultural environment. So, over time, “culture modulates our bloodthirsty tendencies.”

What is particularly original about this study is that it places human violence against the backdrop of general mammalian and primate lethal behavior. The researchers found that there is a correlation between the level of intra-group violence of those species that lie close to each other on the evolutionary tree.

At the start of the U.S. invasion of Iraq in 2003, President George W. Bush ordered the U.S. military to conduct a devastating aerial assault on Baghdad, known as "shock and awe."

At the start of the U.S. invasion of Iraq in 2003, President George W. Bush ordered the U.S. military to conduct a devastating aerial assault on Baghdad, known as “shock and awe.”

In order to come to this conclusion the authors of the study (who are evolutionary biologists) looked at the available data on in-group violent deaths in 1,020 mammal species. From this information they tried to approximate how murderous each group is. For conclusions about the human propensity for murder, the researchers looked at 600 human groups stretching back as far as 50,000 years ago. It turns out we are less violent than baboons and more violent than bonobos, while about as violent as chimpanzees.

Just for the reader’s information, it seems that killer whales almost never hurt each other, and bats and anteaters are quite peaceable to others of their kind. On the other hand, if you’re a cougar, chinchilla or marmot, things can get very dangerous and one has to stay wary of the neighbors.

Getting back to humans, almost every serious historian knows that our propensity for lethal violence has been around for as far back as we can go. Thus the proposition that this behavior is inherited from our pre-human ancestors seems reasonable. However, there is an effort on the part of some researchers in this field, including those who wrote the Nature article, to make the argument that humans are getting less violent.

For instance, this study claims that among Paleolithic hunter-gather groups, roughly 2 percent of deaths were the result of lethal violence. Later, in medieval times, this allegedly jumps to 12 percent. But in the modern age, with “industrialized states exerting the rule of law,” the rate appears to have fallen to 1.3 percent. Is all of this really accurate?

The authors are not the first to make this claim. The Harvard psychologist Steven Pinker, in a 2011 book entitled The Better Angels of Our Nature, argues that humans can and have lowered their level of interpersonal violence through creating institutions and laws that discourage such behavior.

As a general rule we should be wary of such sweeping claims about behavior over such large expanses of time. As one observer of the Nature study commented, much of the data [sources range from archeological digs to modern crime statistics] is “imprecise.” The same is true of Pinker’s evidence. It is due to just such challenges that such studies present these claims in terms of statistical models.

Evolution and Culture

There is much more that can be said about what may well be our species’ “innate tendency to solve problems with violence.” For one thing, it often appears to be territorial. Human beings, nomadic or otherwise, stake out territory and then defend it. This is obviously similar to what certain other primates, close to us on the evolutionary tree, do and so it is reasonable to assume an evolutionary derivation for this behavior.

An American soldier carries a wounded Iraqi child to a treatment facility in March 2007. (Photo credit: Lance Cpl. James F. Cline III)

An American soldier carries a wounded Iraqi child to a treatment facility in March 2007. (Photo credit: Lance Cpl. James F. Cline III)

As societies developed – got larger and more complex – efforts arose to control destructive behavior within in-groups. These took the form of the laws referred to by Steven Pinker as well as the present authors. However, sometimes the data seems to belie this claim.

For instance, why should the medieval period be so much more violent than the Paleolithic if societal institutions and laws were so much more developed at that later time? There might be extenuating circumstances to explain this, but the glitch does suggest that an overall answer to why the rates of lethal human violence go up and down is complicated and multifaceted.

And, what can we say of the modern era, which is supposed to be humankind’s least murderous epoch? If the statistics are correct – which seems counterintuitive – we should be reassured. However, less reassuring is the fact that our technological know-how has also supplied modern mankind with nuclear weapons and thus the ability to wipe out our species, and most all the others too.

There may be a glimmer of hope for a more peaceful future if indeed our violent inclinations are tied to acquisition of territory, and within those territories we usually make efforts to minimize intra-group violence. Under those circumstances one can speculate that the development of ever larger states (culminating in a world state) with ever larger in-groups (culminating in humanity as a single in-group) seems the way to go. Then, in theory, law and order within these expanding categories would make for a more peaceful world.

Just to interpose this part of the analysis into today’s U.S. politics, we can note that the Republican presidential candidate, Donald Trump, wants to make the country’s collective in-group smaller by deporting hundreds of thousands and closing the borders to thousands more. Such a policy can only make the United States more insular and subject to the paranoia of a heightened us-versus-them worldview.

On the other hand, the Democratic candidate, Hillary Clinton, seems to be advocating a hawkish foreign policy that emphasizes the need to control foreign territory directly or by proxy but with no inclination to increase the in-group. This too can only make the world a more dangerous place. The view of one candidate or the other being a “lesser evil” might depend on whether you are focused on domestic or foreign policy.

Whatever the optimistic claim of the Nature study about today’s comparative level of lethal violence, it seems pretty clear that our laws are not doing well enough to supply the peaceful future most of us hope for. For instance, international human rights laws are so infrequently enforced as to be of minimal effect. And, as current migrant crises around the world make clear, the prospects for ever larger in-groups are but a dream.

All of this only gives added credence to the notion that our willingness to slaughter each other is innate – an adaptive habit of a long evolutionary history. This conclusion is offered as an explanation rather than an excuse. For, as the Nature study authors recognize, culture can impact such behavior – tamping it down at least within a designated in-group.

Yet it is hard to shake the feeling that our addiction to lethal violence is our evolutionary fate, and that it hangs there, like a sword of Damocles, always ready to impose itself should the delicate strand of law snap.

Lawrence Davidson is a history professor at West Chester University in Pennsylvania. He is the author of Foreign Policy Inc.: Privatizing America’s National Interest; America’s Palestine: Popular and Official Perceptions from Balfour to Israeli Statehood; and Islamic Fundamentalism.

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20 comments for “Are Humans Natural-Born Killers?

  1. Tatarewicz
    October 11, 2016 at 8:16 am

    Humans are killers to the extent evolution has programmed us to prepare physiologically, including having necessary hormones instantly, against threats to our existence. Hormones used up in fight or flight response.

    Same hormones are produced in today’s perceived threats. annoyances but usually not dissipated by fight or flight so they have a corrosive effect on heart and other organs. To relieve associated stress some kill, for example, a policeman, or punch the “bugger’ or even some random person.

  2. JAMES GARNETT
    October 10, 2016 at 6:14 pm

    If you measure by percentage of fatalities, you get statements like the one in the article, “It turns out we are less violent than baboons and more violent than bonobos, while about as violent as chimpanzees”.
    Let’s see, in the twentieth century alone, humans murdered several hundred million people. So all you are really saying is that really huge populations of humans have a lower percentage rate of murder than chimpanzees. Is this some kind of statistical shell game? Chimpanzees have very small populations, which are subject to basically being hunted, captured for zoos and scientific experiments, Their populations are all highly stressed, and in decline. Resources are scarse. Who knows how violent they were before humans basically invaded their territories? It’s like the old joke where a scientist get a flea to jump on command, then pulls off its legs one by one, commands it to jump after each amputation, which it does, and when the flea has no legs left, and cannot jump anymore, the scientist says, jump, jump, little flea, and when it does not, writes, flea with no legs becomes deaf.

    • Peter Loeb
      October 11, 2016 at 7:50 am

      AVOIDING VIOLENCE OF COLONIAL INVASION AND CONQUEST

      Professor Davidson’s analysis avoids the quintessential
      violence advocated in the Bible which are applauded. Such violence
      has been replicated in colonization for centuries. (Specifics differ, of course.)

      A counteranalysis is available in Michael Prior CD’s excellent
      work THE BIBLE AND COLONIALISM: A MORAL CRITIQUE.

      Other analyses in individual ways confirm Prior’s conclusions.
      Or rather, Prior presents a thorough summation of considerable
      volume of achaelogical work which has been completed.

      (See Prior, Chapters 6 and 7, op cit)

      Conclusions highlighted by Prior are applicable to other
      colonial adventures in different ways. Some of the
      adventures included the genocide by the Spaniards
      after Christopher Columbus whose nameday was just
      “celebrated” in the US.

      —-Peter Loeb, Boston. MA, USA

  3. F. G. Sanford
    October 10, 2016 at 5:46 pm

    Well, if my hard-earned degree in anthropology is still worth anything, I have some bad news for all of you. Chimpanzees do hunt, and they do eat meat. Raw. They obtain it by hunting. Collectively and cooperatively. In other words, they gang up on the prey to tire it, corner it, and then share it based on a dominance hierarchy. They don’t do it routinely or frequently, but they do it. If I were to be dropped unwillingly into a jungle, I would prefer to be surrounded by Gorillas than Chimpanzees. But the real consideration here is linguistic, not innate killing tendencies. There is a range of variation in all species and in all parameters. Those species which exhibit social dominance/submission characteristics, and to some extent tend toward fratricide, are generally “sexually dimorphic”. In other words, the males look different than the females. Size, musculature, distribution of body hair, external genitalia and secondary sex characteristics are all VASTLY different in humans. We are distinctively “sexually dimorphic”, even more so than chimps and gorillas. A contrary example is provided by spider monkeys. Males and females are almost exactly the same size. The female clitoris is the same size and shape as the male member, making males and females indistinguishable at a distance. Some have speculated that this discourages predators, who would lack the certainty that their selected target is a less combative female. But I really don’t think these things essentially matter in the human species. We have “language”, which supersedes all those other potentially selective considerations. Language permits “culture”, which entails distributing shared information laterally and also vertically through successive generations. We know who our grandfather was; Gorillas don’t. But, that same language permits complex abstraction, and subsequent abstractions based on previous abstractions, many of which may be false. It also permits CATegorization and DOGmatization, which lead to animalized behaviors. The primary senses, as limited as they are, still produce observations which may at best be characterizes as ‘first order’ abstractions. Any subsequent statement about those become higher order abstractions: in other words, abstractions based on abstractions. Just my opinion: there are two subspecies of humans currently occupying our planet. One is aware of this phenomenon of rationalizations based on previous abstractions, and the other is not. For the latter group, “facts are facts”, and once internalized, nothing can change their minds. This group comprises probably 90% of humanity. These are the Ken Hovinds, Billy Grahams, Jerry Falwells, Joe McCarthys, Bill O’Reilleys, Stanton Friedmans, David Dukes, etc. Oddly enough, this group also includes some towering intellects. I would include the late Christopher Hitchens, a staggeringly brilliant rhetorician. The group aware of its own abstracting pitfalls includes the Neil DeGrasse Tysons, Bill Nyes, George Carlins, Peter Dale Scotts, George Orwells, Aldous Huxleys, Mark Twains – and many of the journalists who appear on this site. The ability to label, categorize and ultimately call for the termination of other human beings based on falsely interpreted abstractions is at the heart of – if not all, then certainly genocidal – murder. It’s also at the heart of psychotically delusional religious belief. The bottom line? About 10% of “humanity” has reached human maturity. Based on current events, they represent a minority too small to save us. Equal participation in democracy may yet prove to be its own undoing…not, mind you, that I would advocate any other form of government. So far, it’s the best we’ve got, but we’re not using it very well.

    • Zachary Smith
      October 10, 2016 at 6:46 pm

      They don’t do it routinely or frequently, but they do it. If I were to be dropped unwillingly into a jungle, I would prefer to be surrounded by Gorillas than Chimpanzees.

      Given my druthers, I’d rather be dropped into a group of spear-carrying humans who quickly defined me as one of them – another human.

      Regarding the essay title, I’d say that of course we’re natural born killers. All of us. Evolution has forged a tight-knit solidarity among those who have many things in common. And of course a common language is a big one. Black people in the US had the misfortune of being defined as subhuman from the very first settlements, and that has caused them problems ever since – a black skin is very unlike most other colorations. Never mind that they’re identical in all other ways. In the slave south it got so bad that a single known negro ancestor was enough to condemn a person, no matter how lilly-white his or her skin. When times are hard, or made hard by things like extreme inequality, the Rich People set themselves up for pitchforks and guillotines. Because of the evolutionary drive to reproduce, we tend to become overpopulated and that’s a major stress item to a society. Lots easier to be friendly to neighbors when there is always enough to go around. Our big brain causes us problems with the fantasies we create – like My Religion Is Better Than Your Religion. Major wars have been fought over this, though I suspect population stress is somehow behind even the religious conflicts.

    • evelync
      October 11, 2016 at 12:06 am

      Thanks, F G Sanford for your fascinating comment.
      Is it correct that Homo Sapiens and Neanderthals are both part of our genetic structure? If so could
      one of those species’ genetic structure produce a Jerry Falwell or Dick Cheney and the other species’
      genetic structure produce a George Carlin or David Hume?
      Could that explain the difference between say a neocon and a humanitarian?
      Thanks, again

    • Erik
      October 11, 2016 at 8:29 am

      Interesting contrast of those who can conceive that they may be wrong v. those who cannot. I would suggest that this too is not innate (like hunting among chimps) but a product of circumstance.

      For example, among senior engineers one seldom sees a refusal to consider a suspicion that a design idea may be wrong. They know that a missed error will bite them when the design is implemented. Junior engineers are far more willing to chase down a wrong idea just for fun, even when their isn’t time for a second try, and they get bitten or overruled. But fewer engineers are critical of ideas that do not bite if wrong, such as worldviews that grant themselves special rights, or religious or racial prejudices. So skepticism comes down to experience indicating the personal danger of error.

      But there is seldom any personal danger perceived from error in foreign policy or discriminatory domestic policy. There, as in hunting, the individual simply perceives an advantage and has no sympathy or moral constraint.

      The failure of sympathy and moral constraint is mostly a matter of early learning. Those who cannot bully or have not learned to bully, are more likely to sympathize with the unfortunate, accept moral principles, uphold a social contract, and accept a moral argument for a policy. The strong can be so taught. But those who learn to dominate have no sympathy or social contract beyond necessary conformity. And they are the ones who most commonly rise to power within business and politics.

      The tragedy of our society is that it literally fell for the false argument that economic efficiency requires unregulated economic power. Thereby we have empowered bullies to make policy, and they have no sympathy or social contract beyond the rule of the gang, the law of the jungle. That is why we have savages in control of mass media and elections, and savages to choose from as leaders.

      • Erik
        October 11, 2016 at 8:52 am

        I should add that there are also many people who did not learn in childhood to dominate by threats and pushing, who have learned to dominate by tricks and deception. They also succeed in business and politics, and they are perhaps worse than the simpler bullies. We can take our pick of leaders from the worst elements of society, and no others.

    • F. G. Sanford
      October 11, 2016 at 10:48 am

      Thanks to all for the responses. I don’t know how to answer the Neanderthal gene question…DNA behavioral determinants were a new idea in my day, but ‘heredity’, the phenotypical expression of the genotype, was certainly regarded as a legitimate influence to be researched. Some maintain that Neanderthals were more pacific than Homo sapiens, but that their apparent lack of “art” implies cognitive skills inferior to modern species. That may or may not be a valid assumtion – the fossil record may lack examples of what they could or did produce. Another theory claims that, because of the anatomy of the hyoid bone, they were incapable of producing vowels, thereby limiting their capacity for spoken language. Again, “click talkers” demonstrate that vowels are not necessarily essential. I suspect that a great deal of Christopher Hitchens’ erudition stemmed from assiduous study of philosophers like Hume. He could regurgitate it, but never would have independently invented it. A great example of the two distinct personality types is a debate between Hitchens and Michael Parenti. Parenti seems uncertain, tentative, indecisive, and yet at the end of the debate, just my opinion – Parenti has completely crushed the cognitively rigid and inflexible Hitchens. It’s on youtube, but I forget the title. Thanks again – ciao!

  4. Regina Schulte
    October 10, 2016 at 4:18 pm

    I claim no professional expertise in this matter; but I have lived long enough and continued my education in the humanities long enough (I am a lifelong, now retired, academic–M.A., Ph.D) to form the following theory: “Nature,” as we know it in* our planet, is not benign. Walt Whitman referred to that with his description of nature as “red in tooth and claw.”

    Earth vibrates with energy seeking to emerge in life. Thus, we have the millions of flora and fauna species, all absorbing the planet’s ingredients as they strive to preserve and promote their own being–tenaciously. And (this is a big “and”), these ingredients include other species–which they feed upon or kill–choking off food supplies by means of over-production. Humans are participants in this enterprise of killing, eating, starving, absorbing other creatures. Although only in rare instances have we eaten members of our own species, we are now engaged in human-on-human violence on a massive scale as we jockey, jostle, fight, bomb, destroy people in order to grab selfish control of the earth’s resources–to claim that “our religion/nation/ethnicity/government/power/corporate rule/ wealth is the greatest.”

    This is tragically portrayed in what we see happening in the daily global news. War-mongers are threatening even more hostilities and some may trigger the use of nuclear weapons–which several nations now have at hand. (Nearly 50 years ago, in 1967, the Outer Space Treaty went into force, prohibiting the placing of weapons of mass destruction on the moon or elsewhere in space. In other words, the spreading of violence by humans is now that imaginable.)

    Additionally, there is devastation and death, famine, and suffering from the acts of raw nature which we cannot effectively control: hurricanes, tsunamis, droughts, earthquakes, wildfires, etc. However, more and more of these are apparently being caused by the warming of Earth consequent upon human “progress.” Therefore we can exercise some control over their frequencies and brute power.

    Much of the irony in all of this is that human intelligence, evolved through the primates (to which we belong) and ongoing among us, is developed enough for us to address and mitigate, if not totally overcome, the threats to life in* our planet. The challenges are that 1) all peoples abandon competition and divisiveness, work together and apply our (evolved) intelligence toward the saving of all life. And that 2) we begin immediately. It is a project that will desperately require the entire human community.

    It is contrary to our intelligence and our ‘natural’ striving for life for us to abandon hope.

    *Note that we are not “on” this planet; we are “in” it; i.e.,components of Earth.

    • Erik
      October 10, 2016 at 4:49 pm

      Yes, selfishness is the problem, and traditional moral educational systems – religions – have utterly failed to teach cooperation among distinct systems, or to educate the fortunate to sympathize with the unfortunate. There are good and bad members of every religion, but most members of each religion think it has the one true language of morality and the one effective means to teach it. Those who learn in one religion would have learned in any other. In fact religion does not teach morality, because recommending good principles is only a fraction of the social & moral education process. It is taught by experience, but most cannot have the necessary educational experiences, except in literature or other media, because they are rare, dangerous, or require wise interpretation.

      The social & moral education of literature and other media has failed to gain any market share in our money-controlled society, because the mass media are controlled by money. In fact our society has been taken over by business bully-boys who control mass media and elections with money. They are the enemies of any form of morality and actively suppress and attack it. They are the savages who have led us back to the primitivism of ancient times, so that humanity under unregulated market economies must now retrace its prior progress in regulating direct power, but in the context of economic power. Hence their war on socialism, the target of nearly every US war since WWII.

  5. Ol' Hippy
    October 10, 2016 at 3:02 pm

    The innate violence of humans can be mitigated by raising children with real love and non-violent behavioral modification. If interested read: Alice Miller’s works; ‘For Your Own Good’ is especially telling and Jean Liedloff’s ‘The Continuum Concept’ explains a better way to treat babies. Humans can be especially violent when pushed too hard or fighting for scarce resources like food but on the whole I do believe we are less violent now than any other time in history. Also worth a look is Michael Shermer’s ‘ The Moral Arc’ which makes a good case that our society is less violent now than in the distant and recent past. The 20th century seemed especially bad from my perspective but the past has less data points to really get a good comparison. I’ve been peaceful my whole life so maybe there’s still hope at least for a while anyway.

  6. Bill Bodden
    October 10, 2016 at 1:39 pm

    Man’s nature is not essentially evil. Brute nature has been known to yield to the influence of love. You must never despair of human nature. – Mahatma Gandhi

    • Ol' Hippy
      October 10, 2016 at 3:05 pm

      Well said; read my comment below?, in which I sort of make a similar case for loving our children.

    • Gregory Kruse
      October 10, 2016 at 3:35 pm

      Yeah, well what does he know? Love much more often has been known to yield to brute force.

  7. Tom Welsh
    October 10, 2016 at 10:50 am

    ‘But in the modern age, with “industrialized states exerting the rule of law,” the rate appears to have fallen to 1.3 percent. Is all of this really accurate?’

    No. There is still a very great deal of killing going on, but in some cases it is deliberately overlooked or downplayed. Take the US attacks on Iraq since 1990, for example. According to the well-researched and credible two-volume study “Genocide in Iraq”, Vol I: “The Case Against the UN Security Council and Member States”, and Vol II: “The Obliteration of a Modern State”,Dr. Abdul-Haq al-Ani and Tarik al-Ani estimate conservatively that 2.8 million Iraqis have died as a result of deliberate acts by the US government. Significantly, by far the greatest number were not killed outright by military action, like the hundreds or thousands massacred on the notorious “Highway of Death”. https://en.wikipedia.org/wiki/Highway_of_Death The number killed by indirect methods is orders of magnitude higher, including (for instance) the 500,000 Iraqi children responsibility for whose deaths was openly accepted by Secretary of State Madeleine Albright on TV. https://www.youtube.com/watch?v=omnskeu-puE Broadly speaking, the technique is to bomb cities and their infrastructure, destroying sewage plants and pipes, fresh water supplies, hospitals, etc.; and then to impose sanctions that prevent vital medicines, food and other necessities from reaching those who need them. Then sit back comfortably and wait for the many infectious diseases endemic in a hot country to take their toll.

  8. Tom Welsh
    October 10, 2016 at 10:33 am

    ‘At the start of the U.S. invasion of Iraq in 2003, President George W. Bush ordered the U.S. military to conduct a devastating aerial assault on Baghdad, known as “shock and awe.”’

    More accurately known by the older term, “Blitzkrieg”. For some reason, the US government preferred not to use that term.

  9. Drew Hunkins
    October 10, 2016 at 10:33 am

    In the right circumstances virtually all humans can be killers, in times of famine, exploitation, scarcity, desperation, or in times when massive state propaganda’s incessantly drumming up irrational fear, under all these conditions homo sapiens are indeed capable of killing other humans, not to mention our global environment. But at other various times when the human spirit demands solidarity and a speaking of truth to power, homo sapiens can show a remarkable amount of compassion and ability to see through the baloney. It’s this latter tendency that’s built a cooperative and somewhat (somewhat!) egalitarian civilization, to the degree that these factors exist today.

  10. Erik
    October 10, 2016 at 10:04 am

    Looking for innate “tendencies” is a dead end that leads to simplistic fatalism, usually serving a hidden agenda. There is little evidence that willingness to kill is really innate. Lesser primates do not hunt and kill mammals for food, and killing within a group reduces survival rates.

    The evidence is that anger suggests simple solutions to frustrating problems, including competition between primates, and that most people are dumb enough to give anger a try when they don’t know the cause of a problem or have a solution. In addition, the social dynamics of the ignorant suggest killing as a magical solution, or a result of group dynamics.

    Ignorance, selfishness, hypocrisy, and malice are the causes of human wrongdoing, not innate tendencies. But civilization makes uncertain progress against those causes, in large part because it does not try to improve itself.

    Literature has become content-free entertainment, not social and moral education. The mass media are propaganda businesses. Democracy is gone. Only the forms of civilization remain. The former US is not more than an empty suit of armor blundering around the globe, swinging its sword madly. Most of this decay is due to the control of the US by money power.

    • Sydney
      October 10, 2016 at 11:19 am

      Erik is quite correct.
      Moreover, please note that in the original paper the authors clearly state right at the beginning of the article, that they ASSUME that violence is innate. They present no evidence that it is. Indeed as Erik says, there is no evidence. Nor is it possible to look for such imagined evidence, because humans have always been social and therefore no study, genetic or any other about human behaviour can be taken seriously if it does not include intrinsically a study of the specific social conditions of each epoch of human history.

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