(10,000 year old skulls found at Nataruk in Kenya – Image Credit: Marta Mirazón Lahr)

On January 21, 2016 I posted a tweet that read:

Sorry blank slaters & Peace & Harmony Mafia: “Evidence of a prehistoric massacre extends the history of warfare.” http://bit.ly/1PpHvv7

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The reference is to those who adhere to the blank slate theory of human nature and those rather aggressive anthropologists who insist that war is a recent invention and that our ancestors lived in relative peace and harmony with one another and nature. The link is to a recent archaeological study that uncovered the fossilized remains of 27 prehistoric hunter-gatherers who were massacred around 10,000 years ago at a place called Nataruk near Lake Turkana in Kenya. Most of the skeletons showed signs of a violent death: blunt-force trauma to the head, broken hands (some of which were bound), shattered knees, cracked ribs and, most revealing, arrowhead projectile points in the skull and thorax and arrow lesions in the neck. The research team, headed by Dr. Marta Mirazon Lahr from Cambridge University, concluded that one band of people was most likely attacked by another band, explaining:

The deaths at Nataruk are testimony to the antiquity of inter-group violence and war. These human remains record the intentional killing of a small band of foragers with no deliberate burial, and provide unique evidence that warfare was part of the repertoire of inter-group relations among some prehistoric hunter-gatherers.

It is difficult for archaeologists to interpret motive from fossils, but Lahr suggested:

The Nataruk massacre may have resulted from an attempt to seize resources—territory, women, children, food stored in pots—whose value was similar to those of later food-producing agricultural societies, among whom violent attacks on settlements became part of life. This would extend the history of the same underlying socio-economic conditions that characterise other instances of early warfare: a more settled, materially richer way of life. However, Nataruk may simply be evidence of a standard antagonistic response to an encounter between two social groups at that time.

In response to my tweet, my friend David Sloan Wilson, an evolutionary biologist and anthropologist, tweeted in response:

I have to ask: how does an ancient massacre bear upon any of the assumptions of ‘blank slate’ psychology?

I replied:

Blank slate assumption: war is a modern invention w/no relation to our evolutionary propensity to aggression.

Debating deep questions in 140 characters is problematic at best, so David penned a thoughtful essay titled “In Defense of the Blank Slate”, in which he expanded his tweet into a thesis:

The concept of the human mind as a blank slate implies that people are unconstrained in how they behave. That is why I was puzzled by Michael’s tweet. If the human mind is a blank slate, then why couldn’t “war” have been written upon it as well as “peace” 10,000 years ago in Kenya?

Why indeed?

David goes on to discuss the various uses of the blank slate concept in evolutionary theory, such as “the adaptive component of human behavioral phenotypic plasticity,” and the important distinction between levels of causation as outlined by Niko Tingergen: function, phylogeny, mechanism, and development. But here I think David is using the blank slate concept in a way different from how I was thinking of it (restrained, as it was, by 140 characters), and how most people use it, and as such I don’t think David is a blank slater at all and his essay is more prescriptive (how we should think about human nature) than descriptive (how people do think about human nature). So allow me to expand beyond the twitterverse and into the blogosphere with an explanation, which will be shorter than the chapter-length treatment I give it in my 2015 book The Moral Arc.

When it comes to war, the general idea among blank slaters seems to be that if it is ancient and part of our prehistoric past (as indicated by the butchered remains at Nataruk), then that implies an evolutionary heritage, which suggests a genetic component, which carries an implication of biological determinism, which means we will forever be stuck with war because you can’t change human nature. By contrast, if war is a recent invention and the product of civilization and its discontents (overcrowding, limited resources, expanding territories, imperialism, and the like), that means it is a learned phenomenon that carries the inference of cultural determinism, which means we can change war by changing culture.

The overlap of the theory of the blank slate with that of the noble savage has a long historical trajectory thoroughly documented by Steven Pinker in his luminous and wide-ranging 2002 book, The Blank Slate: The Modern Denial of Human Nature, starting with the translation of the medieval Latin term tabula rasa, as “scraped tablet,” which when applied to the mind means it is empty of innate ideas, concepts, emotions, and the like. John Locke is credited with popularizing it in his 1690 An Essay Concerning Human Understanding, when he asked readers to “suppose the mind to be, as we say, white paper void of all characters, without any ideas. How comes it to be furnished?” His answer, empiricism, is more commonly thought of as experience or culture. Around that time, in 1670, the British poet John Dryden penned this expression of humans in a state of nature: I am as free as Nature first made man / When wild in woods the noble savage ran. In 1755, the French philosopher Jean Jacques Rousseau canonized the noble savage into Western culture by proclaiming:

So many authors have hastily concluded that man is naturally cruel, and requires a regular system of police to be reclaimed; whereas nothing can be more gentle than him in his primitive state, when placed by nature at an equal distance from the stupidity of brutes and the pernicious good sense of civilized man.

Pinker draws the historical link between beliefs about human nature and war: “First among the authors that Rousseau had in mind was Thomas Hobbes,” whose theory of human nature could best be described as an ignoble savage. As Hobbes wrote in his classic 1651 book Leviathan:

In such condition there is no place for industry, because the fruit thereof is uncertain: and consequently no culture of the earth; no navigation, nor use of the commodities that may be imported by sea; no commodious building; no instruments of moving and removing such things as require much force; no knowledge of the face of the earth; no account of time; no arts; no letters; no society; and which is worst of all, continual fear, and danger of violent death; and the life of man, solitary, poor, nasty, brutish, and short.

As Pinker demonstrates, one reason intellectuals prefer Locke’s and Rousseau’s theory of human nature—one that combines the blank slate and the noble savage—over Hobbes’s bellum omnium contra omnes, is that “for centuries the stereotype of the savage was used as a pretext to wipe out indigenous peoples and steal their lands.” But as Pinker insightfully reminds us, “surely it is unnecessary to paint a false picture of a people as peaceable and ecologically conscientious in order to condemn the great crimes against them, as if genocide were wrong only when the victims are nice guys.” Nor, he adds, does a realistic theory of human nature—one that includes an evolved capacity for violence and war—“mean that our species has a death wish, an innate thirst for blood, or a territorial imperative.”

If I am reading David’s analysis correctly he rejects the blank slate model of human nature, as do I, and instead embraces a model that includes evolved templates and programs with which culture and experience interact. So this really comes down to the empirical question of whether or not warfare—or violent conflict—was part of our Environment of Evolutionary Adaptedness (EEA) and thus part of our evolved nature. In The Moral Arc I provide copious evidence that it was, but I also propose that instead of thinking of human nature as being either pacifist or bellicose, we should think of aggression and violence as emotions and behaviors that evolved in response to free riders, bullies, challenges, and threats to the survival and flourishing of individuals and groups in the EEA. That is, the data I review are meant less to settle the debate that has long raged about what humans were like in a state of nature and instead build on the logic of our moral emotions and how they direct us to respond one way or another to other sentient beings who, in turn, respond to our actions accordingly.

The full development of this idea, and the massive dataset demonstrating that violent conflict was part of our evolutionary heritage (into which the Nataruk massacre discovery fits well) is much too long for an essay such as this, so I will conclude here by noting that an underlying goal in the study of the nature and causes of violence and war—whatever the correct blend of biology, culture, and circumstance turns out to be—is to attenuate them. Because the stakes are so high, emotions in those who conduct such studies run deep (see, for example, the journalist John Horgan’s tireless defense of the war-is-recent position and his interpretation of the Nataruk find). The economist and evolutionary theorist Samuel Bowles, who has written about the evolution of cooperativeness, said it best in a casual remark to me when I interviewed him for my book:

It seems to be a highly ideologically charged debate, which is unfortunate, because finding that war was frequent in the past, or that out-group hostility might have a genetic basis says something about our legacy, not our destiny.

Published On: February 1, 2016

Michael Shermer

Michael Shermer

Michael Shermer is the Publisher of Skeptic magazine, a monthly columnist for Scientific American, and a Presidential Fellow at Chapman University. He is the author of numerous bestselling books, including The Science of Good and Evil and The Moral Arc: How Science and Reason Lead Humanity Toward Truth, Justice, and Freedom.


  • Lorenzo from Oz says:

    I agree, Prof. Wilson is indeed not using the term “blank slate” in its normal meaning. As I noted in a comment on his post, equilibrium thinking is not really “blank slate”: it is assuming that the thing being modelled is at rest, and then looking at what happens when some factor upsets the equilibrium. The equilibrium may be quite complex but still be at rest. If it was a genuine “blank slate” adding a new factor would have no effect, because there would be nothing for it to have an effect on.

  • Chris Kavanagh says:

    Nice to see a response! And like Lorenzo I agree that David’s original article used a rather unorthodox definition of the ‘blank slate’ to defend, indeed I said as much: http://god-knows-what.com/2016/01/29/redefining-the-blank-slate/

    There is also a nice balanced assessment of the finding available on Peter Turchin’s blog:

  • Chris G says:

    Interesting stuff – I must get round to reading ‘The Moral Arc’ soon. Minor point: you’ve spelt Niko Tinbergen’s name wrong.

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