Category Archives: Evolution

To End War, We Need to Understand Its Origins, Evolution and Causes

Michael L. Wilson and Richard W. Wrangham

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In a recent opinion piece for Scientific American, John Horgan writes “Ending war won’t be easy, but it should be a moral imperative, as much so as ending slavery and the subjugation of women. The first step toward ending war is believing it is possible.” As part of his argument he declared that “far from having deep evolutionary roots, [war] is a relatively recent cultural invention.” We cherish the goal of ending war, but regard the claim of war being independent of our evolutionary past as unjustified, irresponsible and improbable. It is possibly based on a misunderstanding of what it means for a behavior to have evolutionary roots, but regardless of its derivation, we see it as dangerous. The problem is that if Horgan’s view prevails, we close our minds to potentially important contributions towards understanding the causes of wars.

Like any other sane individual aware of the power of nuclear weapons, we of course agree that is desirable to reduce major wars to zero. We consider this goal to be part of the “possibilist agenda” —  an approach that begins by ruling out what is impossible, given the laws of the universe, rather than pessimistically focusing on what results are most probable to occur. 1  Is ending war possible? Well, we don’t know of any laws of physics, or even principles of evolutionary biology, that would make it impossible to end war. The task before us remains finding the best means to achieve this goal. This includes gaining a clear, scientific understanding of what war is, what its causes are, and what factors can prevent it.

There are reasons for optimism. The examples Horgan cites shows that extended peace is a reasonable possibility, given that wars have been absent for decades in parts of the world. As Stephen Pinker described in exhaustive detail in his 2011 book, The Better Angels of Our Nature, deaths from international warfare declined steeply after 1945. Many of the richer countries that formerly engaged in long and bitter wars with one another — the United States, Japan, Germany, France, England — are currently closely allied in long-term friendships. The United States and Canada, for example, haven’t fought each other in earnest since the War of 1812, and as each other’s largest trading partners, benefit greatly from trading rather than invading. At the same time, the rise of authoritarian and nationalistic leaders worldwide, and events such as Russia’s invasion of Ukraine, provide reasons for concern. 

We also agree that much about war involves “relatively recent cultural inventions.” Certainly contemporary weapons are entirely different from those used by the hunter-gatherers of Nataruk, Kenya, 10,000 years ago to execute their enemies, or by the several hunter-gatherer societies of India’s remote Andaman Islands who lived in permanent war with each other. Equally novel are the hierarchies that give leaders power to order warriors into battle, and the military training that promotes efficient tactics, and ideologies that encourage self-sacrifice even to the point of suicide, and the assembly of huge armies. There are many such novelties. But so what? They cast no direct light on the question of the antiquity of war, or more importantly on the question of whether the possible practice of lethal intergroup aggression by our remote ancestors has left a legacy in the human psyche.

Whether war has deep evolutionary roots remains an unsettled topic, contrary to Horgan’s assertions. For example, Horgan links to his 2016 blog post, in which he describes a study led by Hisashi Nakao of skeletal trauma in hunter-gatherers living in Japan 12,000 to 2,800 years ago, which reports that only a small proportion of skeletons showed evidence of violent death. However, as noted in a 2020 review by Mark Hudson and colleagues, “[i]ndividual finds of arrowheads embedded in human bones and other similar, clear-cut traces of violence have long been known in Japan as elsewhere.”  Although Nakao and colleagues consider their findings to represent a low rate of violence,  their sample includes cases of “blunt force injuries to the cranium and embedded stone and bone projectile points in the post-crania with no signs of healing – providing a prevalence of 1.8 per cent of adults dying violently.”   

Do these data indicate a high or low rate of death from violence? The actual rate of deaths from violence is difficult to determine from archaeological evidence alone: not all deadly violence damages bones, and only a fraction of deaths end up in the archeological record. But if we take the rate of 1.8% adult deaths from violence at face value, this is about 2.5 times the rate of death from homicide in the United States in 20202, a year marked by a dramatic increase in violence. What does this tell us about the evolutionary roots of war? It provides additional evidence that people in prehistory faced a threat of death from violence, but also provides additional evidence that rates of violence vary across space and time, for reasons that are worth exploring further. 

For anyone seriously interested in understanding the causes of war many other kinds of evidence are thought-provoking. Warfare is documented among hunter-gatherers in every inhabited continent, and was especially prominent where the neighbors were also hunter-gatherers rather than dominant farmers. Chimpanzees, our evolutionary cousins, practice a form of intergroup aggression that is strikingly similar to the hit-and-run aggression characteristic of human small-scale societies. In chimpanzees and in humans the initiators and the victims of lethal intergroup aggression are overwhelmingly males. In both species, males are more aggressive than females, a difference that starts long before maturity.

Why are chimpanzees and humans two of the few species of mammals that regularly take advantage of opportunities to kill members of neighboring groups? Are the reasons wholly different in the two species, or do they share some aspects of motivation and explanation, in which case, what are they? To rule out such questions is unworthy of an essay in a scientific journal. They concern topics being actively explored in behavioral ecology, evolutionary psychology and the neurosciences, among other areas.

There is much to learn, but we believe that some current hypotheses are helpful. One is that warfare has evolved from the human ability for proactive aggression. Proactive aggression involves making plans to attack vulnerable victims using overwhelming power, a practice followed by chimpanzees and humans. It benefits the aggressors by leading to increased territory size, or greater safety. Importantly, however, proactive aggression is very predictably inhibited when potential victims turn out to be sufficiently well defended that the aggressors risk getting hurt. Thus, even though proactive aggression is reined in for most of the time, it pays dividends under some circumstances; and human brains are likely very sensitive to such assessments. Would Russia have dared to invade Ukraine in 2014, much less escalated its attack in 2022, if NATO had accepted Ukraine’s application to join in 2008?

The challenge of preventing major wars is mainly undertaken by politicians and lawyers, but we think that every contribution might help. If a deep legacy of using coalitionary proactive aggression has left its mark on the human psyche, what does that mean for differences in war motivation between men and women? Or for how war leaders perceive the costs of wars in which they are directors rather than participants? Or for the point at which leaders will perceive the benefits of peace as outweighing the costs of war? Or for how individuals categorize others as friend or foe? Is it possible that the psychological mechanisms for evolutionarily-based risk assessments are predictably affected by certain medicines that could make leaders more or less risk-prone? If so, we should all be especially alert to a leader’s ailments. To ignore such questions is to bury one’s head in the sand.

Retaining an open mind about the etiology of war is surely the wisest course in a world still threatened by major conflict, despite the many institutional efforts, from the UN down, to control it.

Additionally, whether war has deep roots in our psyches, or is a recent invention like agriculture and empires, evolutionary game theory suggests that in looking to the future, we need to consider, not just our hopes and dreams, but also the strategies available to all players in the game. Players don’t act in a vacuum: they act in a world of competing strategists. We may prefer to plan for peace rather than war, but if other players pursue war as a strategy, we must either prepare to oppose them, or be defeated by them.

Russia might one day fulfill its promise of becoming a Canada to Europe and Asia: a peaceful, prosperous neighbor to the north. In the meantime, however, Russia’s leaders remain trapped in a zero-sum view of the world, seeing neighboring states more as opportunities for conquest than commerce. 

As an example of a fatalism that will lead to more war, Horgan offers this quotation from Kaja Kallas, the prime minister of Estonia: “Sometimes the best way to achieve peace is to be willing to use military strength.” People living in Estonia, however, have bitter historical experience with being invaded and occupied. If you live next door to Putin’s Russia, rather than Trudeau’s Canada, the best way to prepare for peace may indeed be to prepare for war. International peace will not be achieved by simply giving in. Peace among nations surely requires making the costs of war so high that when appeals to law or morality fail, potential aggressors recognize that it is in their own best interests to find a constructive solution.


Horgan, J. (2016, April 4). Japanese study deals another blow to deep-roots theory of war. Scientific American Blog Network. Retrieved May 12, 2022, from 

Horgan, J. (2022, April 27). Will war ever end? Scientific American. Retrieved May 12, 2022, from 

Hudson, M., Schulting, R., & Gilaizeau, L. (2020). The Origins of Violence and Warfare in the Japanese Islands. In G. Fagan, L. Fibiger, M. Hudson, & M. Trundle (Eds.), The Cambridge World History of Violence (The Cambridge World History of Violence, pp. 160-178). Cambridge: Cambridge University Press. doi:10.1017/9781316341247.009

Nakao, H., Tamura, K., Arimatsu, Y., Nakagawa, T., Matsumoto, N., & Matsugi, T. (2016). Violence in the prehistoric period of Japan: The spatio-temporal pattern of skeletal evidence for violence in the Jomon period. Biology Letters (2005), 12(3), 20160028.

  1.  “Following the possibilist agenda means working tirelessly to imagine both possibilities and impossibilities and then laying plans to arrange events so that the desirable can be realized and the undesirable avoided—working to avoid unintended consequences. In this way, by superposing such thoughts onto recognized physical–biological–social problems of the world . . . seemingly intractable problems may have possibilist solutions.”  PNAS []
  2. Proportion of deaths in the United States from homicide = 0.73% in 2020, based on 24,576 homicide deaths and 3,358,814 total deaths []

Dinosaur Love Songs

The conceptual lenses of evolution completely transform how we see the world.

For example, without thinking about things from an evolutionary perspective, a walk through my neighborhood on a morning in May is pleasant enough, but not particularly dramatic. Elm trees, oaks and maples stand along the boulevard, limbs stretched overhead to make the street a green tunnel, the blue sky barely visible beyond the canopy of leaves.

Elm tree competing with other trees for a patch of sunlight.
Elm tree reaching up for a patch of sunlight.

Honeybees and butterflies visit the irises blooming in the garden. A little black-capped chickadee perches for a moment on a branch above the birdhouse and opens his beak to sing his song, joining the chorus of that fills the morning air.

Looking at this peaceful scene through the lenses of evolution, though, reveals that this tiny little chickadee is a dinosaur. We know now that the dinosaurs didn’t disappear; in fact the number of living dinosaur species (10,000 or so) greatly exceeds the number of mammals (not quite 6,000). This chickadee, like all other birds, is a theropod dinosaur, distant kin to Tyrannosaurus rex. The more we learn about dinosaurs, the more we learn how much like birds they were.  While it’s hard to be certain about the soft tissue, physiology and behavior of long extinct animals, various lines of evidence suggest that, like this chickadee, Tyrannosaurs was a feathered biped with a four-chambered heart, possibly with warm blood in its veins, and (perhaps) a devoted parent.

Poecile atricapillus successfully lured to the dinosaur feeder.
Poecile atricapillus successfully lured to the dinosaur feeder.

The song the chickadee is singing is no idle amusement to pass away the time. It is a matter of utmost importance to him. He sings to claim this territory as his own, to keep all rival males at bay. And why does he care so much this territory? Because this bit of yard and trees will be the home for him and his wife, the mate he seeks to woo with his song. The morning air resounds with the love songs of dinosaurs.

The flowers blooming in the garden and on the lawn are lovely in their own right. But viewing them through the lenses of evolution, we see that, like the songs of birds, they are all about sex. Each flower is a cunningly designed sex organ. The irises growing in the garden have large intricate blooms, with deep purple or yellow petals shading the male and female sex parts within: the female pistil, and the stalks of male stamens. Like the songs of birds, flowers are designed to attract mates. But flowers don’t have eyes, and they can’t move, so in order to mate, they lure other species to help them. While we humans find the vividly colored petals attractive, the iris is really aiming its message at the eyes of bees.

Landing platform for sex workers.
Landing platform for sex workers.

The bottom petal of the iris is an exquisitely designed landing platform for bees. A pattern of colors – likely including colors that bees but not humans can see, in the ultraviolet spectrum – guides the bees down a tunnel into the heart of the flower. There the iris provides the bee with a meal of nectar, while coating the bee with pollen as she sips her meal in the snug chamber. Each grain of pollen protects a cell that will give rise to two sperm cells. Dusted with flower sperm, the bee exists the chamber and flies off to another flower, playing its role in an interspecies ménage-a-trois.

Bumblebee sipping nectar from a bleeding heart flower.
Bumblebee sipping nectar from a bleeding heart flower.

The elms, oaks and maples whose boughs shade the street in green light seem peaceful enough. But viewed through the lenses of evolution, we can see that these trees are fighting a long, slow battle. Each tree is growing as fast as it can to reach the sun. Each tree has many enemies: the caterpillars that eat the leaves; the Dutch elm disease that gnaws at their roots; the summer storms that break their limbs. But no enemy is a more bitter rival than its neighboring trees. Each tree is fighting a slow struggle to reach the sun first, to spread their limbs wide and cover their enemy trees in the darkness of their shade. And why do these trees care so much for the sun?

The sun is life, their source of energy. Each tree is a solar powered sugar factory, holding thousands of flexible green solar panels up to the sky. Shade is death. The tree must grow high above the neighboring trees to reach the sun.

And why must the trees make sugar? So they can make babies. These trees have spent the spring having sex and making babies. Unlike irises and dandelions, though, these trees don’t rely on other species to have sex for them. Instead, they have sex with the wind, releasing their pollen into the air. Not long ago, the greenish yellow dust of tree sperm covered every surface outside: the sidewalks, parked cars, porches, and grills. Now the world is covered with the resulting babies: tree embryos in tiny packages. Some of them have wings: the helicoptering seeds of maples, or the tiny flying discs of elms. Floating in the breeze, and choking the grill of the air conditioner, are the tiny fluffy seeds of cottonwood trees. These trees, growing to giant size along the Mississippi floodplain, make the tiniest seeds, each suspended by a parachute of fluff.

Azalea sex parts. A bit of fluff from a cottonwood seed clings to a flower on the left, and an elm seed is lodged between two other flowers.
Azalea sex parts. A bit of fluff from a cottonwood seed clings to a flower on the left, and an elm seed is lodged between two other flowers.

Year after year, each of these trees makes thousands or millions of seeds. And almost every single one of these seeds will die before it becomes a tree, eaten by birds or squirrels, washed down the gutter to the storm sewer, dissected by children curious about what’s inside a maple helicopter. A fortunate few will land on soil where they can take purchase and sprout – only to be plucked by weeding gardeners, or eaten by rabbits or deer. Only a tiny fraction of all this abundant mass of seeds will ever grow into trees big enough to make seeds of their own.

A pile of doomed elm embryos.
A pile of doomed elm embryos.

Close-up of elm seeds, showing their cunning little hooks for clinging onto seed dispersers. The seed on the right appears to have been killed already, perhaps by a predator.
Close-up of elm seeds, showing their cunning little hooks for clinging onto seed dispersers. The seed on the right appears to have been killed already, perhaps by a predator.

Viewing the world through the lenses of evolution help us see that what seems to be a quiet city street is actually an unfolding drama of sex and violence: seductive flowers, battling trees, and dinosaur love songs.

Amy Kass

In the Odyssey, the goddess Athena appears to young Telemachos in the form of an old man, Mentor. In this guise, Athena tells Telemachus what he needs to do.

At the University of Chicago, Amy Kass appeared to many of us as a Mentor. But she didn’t tell us what to do. She didn’t give us the answers. Instead, she asked us questions:

“Who is someone you think of as an example of human excellence?”

“Is it better to be a virtuoso, or virtuous?”

“What will be the most important decision that you make in your life?”

She didn’t dispense a particular body of knowledge to students: chemistry, physics, classics, literature, or philosophy. Instead, she served as a guide, helping students learn to read great books, and to think seriously about big questions in their lives.

I first met Amy Kass  the summer after my junior year in high school, when I spent six weeks at the University of Chicago for a Telluride Association Summer Program. Amy and another great teacher, her husband Leon, led the seminar, Science and Society: Knowledge Morals and Power. Eager for more classes like this, I returned to Chicago for college, where I took Human and Being and Citizen with Mrs. Kass. We read Homer (the Iliad), Genesis, Aristotle (The Nicomachean Ethics), Shakespeare (King Lear), Rousseau (Discourse on the Origin of Inequality), Kant (Foundations of the Metaphysics of Morals), Dostoevsky (Crime and Punishment), Luke. We read about examples of human beings: Abraham, Achilleus, the Great Souled Man, Lear, Savage Man, Rational Man, Raskolnikov, Jesus. We talked about what, if anything, was excellent about these men (and looking back, yes, in that class, the exemplary human beings were all men).

Class took place in seminars: twenty or so students gathered around a set of tables arranged in a square. We read and we talked. Mrs. Kass asked questions. She was slender and small, with bright eyes and silvering hair. She leaned forward when she spoke, gesturing with her hand, looking intently at each student. We called each other by last names and titles: Mr., Miss, or Mrs. Everyone had a place at the table, and the value of your ideas didn’t depend on your title or rank. Everyone was treated as an adult, and with respect. She encouraged us to speak our minds, and to disagree with her and one another, but to do so through discussions (“What is right?”), not arguments (“Who is right?”).

Amy Kass at the 1986 Telluride Association Summer Program in Chicago.
Amy Kass at the 1986 Telluride Association Summer Program in Chicago.

Mrs. Kass didn’t lecture. She didn’t tell us her views on things, at least not directly. She asked questions and listened to our answers. She knew our names, she knew who we were, and despite her years of teaching these books to students, she seemed genuinely interested in what we had to say about them. How often does a class of first year college students say something really new or surprising about Homer or Shakespeare? But she never seemed jaded or condescending towards her students. She wasn’t interested in whether we could say something clever or novel; she was interested in our development as readers and thinkers.

She led us through the readings slowly. She asked a student to read a passage, then we discussed what it meant. We might spend an entire class period discussing a few such passages.

Mrs. Kass helped teach us to read.

I didn’t know how to read when I started college. Even by the time I finished college I’m not so sure if I could read; these lessons have taken time to really sink in. Oh, I read lots of books, but I skimmed along the surface, and often didn’t even understand the surface. Too often, reading was something I did at the end of a long day of lectures, labs and problem sets, slouching in a big chair in a bay window of the Regenstein Library, underlining and querying a few puzzling sentences before dozing off.

But in class, we read aloud, we read slowly, and we read for understanding.

Mrs. Kass began a discussion of Book IV of The Iliad by asking, “If I asked you who you were, what would you tell me?”

“I’m a 20th Century American.”

“And how does Homer introduce these men? Who is, say, Echepelos?”

“He’s… um….” searching the page for the name, “Thalysias’s son.”

“And Elephenor?”

Okay, there’s his name a few lines down. “Chalkodon’s son.”

In the world of The Iliad, you weren’t an isolated human being, or an undifferentiated member of a particular society in a particular time. You were someone’s son or daughter.

Then we moved on to the next page, where Antiphos, a son of Priam, killed Leukos, “a brave companion of Odysseus,” as Leukos was dragging off a corpse. Odysseus, “stirred to terrible anger,” struck down Demokoön, a son of Priam.1986-07 Eileen Helen Amy Mike Kim Tricia

Mrs. Kass asked, “Why did Odysseys kill Demokoön, and not Antiphos?”

I hadn’t even thought to wonder about this; my eyes had glazed over in the series of seemingly random, bloody killings on the battlefield.

Mrs. Kass persisted. “Who is Demokoön?”

“He’s Priam’s son. Oh. Odysseus killed his brother.”

Instead of seeking revenge by killing the killer, Odysseus inflicted a more painful, longer lasting wound, by killing the killer’s brother. And so a seemingly unimportant detail was revealed as an illustration of the cruel wisdom of Odysseus.

With Mrs. Kass, we read old books. The most recently written thing we read was Dostoevsky’s 1866 novel; not one of her favorites, and one that must have been chosen by others on the course committee, judging by a comment she made after a class spent discussing this book: “This is my punishment; what was my crime?”

One thing we learn from the standard university curriculum is how wrong people were in the past. Aristotle appears in science textbooks mainly as someone who got things wrong: that a heavier object falls faster than a lighter object; that there are four basic elements; that the sex of human babies is determined by temperature. We learn about Descartes’ error (mind-body dualism) rather than anything he got right. The basic lesson of the textbooks is: people in the past were ignorant. They didn’t know germ theory, or atomic theory, or evolution.

And it’s not just in the remote past that people were ignorant. By the time I reached college, scientific views of the solar system, of dinosaurs, and so many other things had changed dramatically from what I remembered learning as a child. Every year, we know so much more than we did before.

It’s easy – and self-gratifying – to be smug about how smart we are today. We know so much more. We are right about so many things.

Mrs. Kass helped us see that despite how much we know now, we still had much to learn from close reading of Homer, Aristotle and Shakespeare, even if they are Dead White Males, even if they lived before the discovery of quantum physics and the genetic code, even if their views on politics and religion might sometimes seem old fashioned (though perhaps not always so old fashioned as one might expect). She helped us understand the difference between knowledge and wisdom.

Despite all the changes over centuries and millennia, much about the human condition remains the same. We are born, we grow up, we search for a path to follow. We seek love and friendship. We may marry, we may have children. If we live long enough, we grow old. Whether we live long enough or not, we die. Even people admired for excellence have their quirks, weaknesses, and sometimes terrible, fatal flaws.

Universities have plenty of classes that provide answers. But few classes ask questions. And hardly any classes ask questions that are really the most important ones for young people trying to find their way in life.

When Mrs. Kass asked her class, “What is the most important decision you will have to make,” most students answered something to do with their careers. One young man responded: “Who will be the mother of my children?”

The answer sounded old fashioned, and embarrassingly serious. But really, what could be more important?

I wanted answers. I wanted to know. While we were reading Kant, I asked Mrs. Kass what was her foundation for morality. She threw up her hands and laughed. “Standing on one leg?” she asked.

If it were that easy – if you could give an answer to this question, standing on one leg like a circus performer – then we wouldn’t need to spend hours reading, thinking, and discussing these questions. A short lecture on moral foundations would do.

We read about many different kinds of human excellence, but none of these literary examples struck me as vividly as the example of Mrs. Kass herself: intensely smart but never merely clever or showy; respectful, but not afraid to question or disagree; inclusive; courageous; serious yet also wry, funny and good humored; challenging us all to be better.

The last time I saw Mrs. Kass, she was discussing with a young person an assignment for a class on Shakespeare, taught by someone else. The student had developed a particular view of how to interpret a passage, but was worried that her teacher would disagree with this interpretation. Mrs. Kass asked her, “Do you want a good grade? Or do you want to be right?”

Amy Kass died Wednesday, 19 August 2015, less than a month before what would have been her 75th birthday.

I have not known a better teacher.

Turing’s Cathedral

On the plane to Ethiopia, and while sweating in my tent at night from the relentless heat at Filoha, I read Turing’s Cathedral, a book my Dad told me I should read. He was right, it’s well worth reading. It’s also timely, as my wife had us watch the movie Deus_ex_Machina for a recent family movie night.

In Deus_ex_Machina, a lone genius constructs an artificial intelligence (AI), which he then subjects to a Turing test to see if she can pass as a conscious being. The movie is thought provoking and disturbing. You can have a brief conversation with the AI, who is named Ava, here. She can even draw a picture of you.

The book Turing’s Cathedral describes the building of one of the first artificial intelligences: the MANIAC computer at Princeton’s Institute for Advanced Studies in the 1940s and 50s. The building of the MANIAC was an intensely collaborative team project. While Hollywood loves isolated mad scientists working in remote lairs, nowadays real scientific advances are usually the result of team effort. No one person can have enough expertise to do everything that needs to be done. AIs that can pass the Turing test will be the result of teamwork on a massive scale.

The book is titled Turing’s Cathedral, but the main character is not Alan Turing (who provided the theoretical foundations for computers), but Johnny von Neumann, who among other things, invented game theory and cellular automata, and played key roles in developing the first atomic weapons and digital computers. Von Neumann was an intensely social genius who built and led the team of people who made the MANIAC, and who traveled extensively, providing intellectual connectivity between Princeton, Los Alamos, Cambridge and other key hives of activity.

The author of Turing’s Cathedral is George Dyson, who grew up at the Institute for Advanced Studies, where his father Freeman Dyson was a fellow. Dyson shows how the development of computers and atomic weapons were intimately linked, and also connected to evolution and genetics. MANIAC’s first job was to run simulations of thermonuclear explosions. Soon after, Nils Aall Barricelli programmed MANIAC to run simulations of evolution.

Evolution, it turns out, is key to thinking about logic, mathematics, and the stuff of thought. One of the central puzzles of mathematics in the early 20th Century was whether all true mathematical statements could be derived from a simple set of axioms. Mathematician David Hilbert argued that “from a strictly limited set of axioms, all mathematical truths could be reached by a sequence of well-defined logical steps.” (Dyson 2012: 49) Bertrand Russell and Alfred North Whitehead tried to do this in Principia Mathematica, which despite covering nearly 2,000 pages “still left fundamental questions unresolved” (Dyson 2012: 49). Von Neumann took on the challenge in 1925 in a paper, “An axiomatization of set theory,” which provided a more concise and more nearly complete answer to the problem. But in 1936, Kurt Gödel published a paper that argued that the project could never be completed, because mathematics was fundamentally incomplete: “within any formal system sufficiently powerful to include ordinary arithmetic, there will always be undecidable statements that cannot be proved true, yet cannot be proved false” (Dyson 2012:50).

This incompleteness of mathematics, and logical systems generally, relates to insight and intuition. Systematic and logical thinking alone can only get you so far. Insights involve leaps, making unexpected connections. Insight is evolutionarily equivalent to mutation: random changes that sometimes result in improvements.

When Turing worked on the Manchester Mark I computer in 1949, he made sure to install a random number generator. This enabled the computer to take advantage of mutations, or “guesses,” and learn from its mistakes.

Intellectual thought, and biological evolution, both depend on two key things: accumulated change, and mutation. Accumulated change ensures that past advances are preserved. Mutation provides the material for new solutions to problems. Most mutations don’t work, but some do. Adding the good mutations to the accumulated wisdom of previous generations permits advances to be made much more rapidly than if everything had to be attempted at once.

During World War II, Turing developed a machine to break the code used in German war communications. The code was too complicated to be solved all at once. But by using a mutating, evolving process, Turing managed to evolve solutions to the problems.

Computers evolve, and DNA is a computer. When Dad told me I needed to read Turing’s Cathedral, he told me, “DNA is a Turing machine!” And he’s right. Dyson doesn’t really develop this point, but he hints at it.

A Turing machine is a universal computer. When Turing proposed the machine in 1936, many people believed that thought was somehow distinct from machines: thoughts are the work of souls, which machines can never have. But Turing proposed that a machine could produce all computable statements. Turing described the machine as having a tape fed into it. The machine can read symbols on the tape, write symbols on the tape, and move the tape left or right. The machine is mindless, but it produces intelligent behavior. Our world today is densely populated with Turing machines running on our computers, phones, and the cloud.

DNA is essentially the tape in a cellular Turing machine. It stores digital information to run the programs that the cell carries out. The cellular mechanisms read the DNA tape, copying portions of it into RNA, which may either be translated into proteins, or used to regulate particular portions of the DNA, or other cellular processes. DNA is mindless, but it acts intelligently. DNA encodes complicated subroutines that involve numerous genes that regulate the production of proteins. But because DNA is digital and universal, in principle it could be used to store any kind of information. Perhaps someday artificial computers will use DNA memories.

For the first few hundred pages, I thought that Turing’s cathedral was the MANIAC computer. But no, as it turns out, the cathedral is Google: that vast conglomeration of Turing machines that knows so much about everyone who has ever searched the Internet. Ava, the AI in Deus_ex_Machina, is created by a man who runs a company, Blue Book, that is a thinly veiled version of Google. Though Ava is created by a lone genius, she learns to understand humans by being granted access to Blue Book searches and cell phone conversations. In this way the AI is created by all of us. And Dyson argues that Google and other online giants, such as Facebook and Amazon, are evolving towards artificial intelligence as they learn from us.

And as computers become more like us, we are increasingly becoming like computers. Reasonably well off people in rich countries have all become cyborgs, and this trend is expanding worldwide. I started becoming a cyborg when Dad gave me an IBM clone computer. This was not my first computer, but it was the first one with a floppy drive (instead of a cassette tape) and enough memory to store what I wrote: papers for classes, college application essays, stories, notes for science fiction worlds, and other personal writings. Soon a substantial portion of what I think of as me was stored on this machine. It didn’t have as much memory as my brain, but it remembered more accurately.

My current laptop retains most of these old memories (though some have been lost through decay, copying errors, failures to store things properly, and loss of compatibility between old files and new programs). But my cyborg existence doesn’t depend on a single machine anymore. Instead it is smeared out across the Cloud: Gmail, Facebook, Dropbox, Snapfish, Google’s memory of my search history, Amazon’s memory of my purchases. The Web may know more about me than I do. With every bit we post, with every search we enter, with every product we buy, we feeding the Web information about human behavior and preferences. We are all building the next AI. And as the Web (or Google or whatever) evolves awareness – well, I hope it is benign.

Works cited:

Dyson, G. (2012). Turing’s Cathedral: The Origins of the Digital Universe, Pantheon.

Words and Genes

This weekend,  people in the United States set off numerous explosive devices to celebrate 239 years of independence from the United Kingdom. Since this separation, the versions of English spoken in the US and the UK have diverged considerably, but still remain (mostly) intelligible. In contrast, North and South Korea, which have only been separated for 70 years, have been more strictly isolated from one another, and as a result the versions of Korean spoken in the two countries have diverged dramatically:

differences [of mutual unintelligibility] now extend to one third of the words spoken on the streets of Seoul and Pyongyang, and up to two thirds in business and official settings.

A friend of mine who is an actual linguist drew my attention to an app that designed to translate between North and South Korean— an acute problem from people who have defected from North to South.

As Darwin and many others have noted, and as I’ve written about here, such language change bears many striking similarities with biological evolution. These similarities are interesting in their own right, and may be helpful for thinking about the long-running debate in evolutionary biology about whether natural selection acts mainly on genes, individuals, or groups.

A language, like English, or German, or French, is like a biological species. Both languages and species are made up of populations of individuals. Languages and species both have boundaries. In biology, the boundary is sex: a species is defined as a population of individuals that naturally mate and produce fertile offspring with one another. This concept is a pretty good rule of thumb, but turns out to be violated frequently in nature. Oak trees are notoriously promiscuous with oak trees from other species. Of course they mate simply by wafting their sperm into the air (tucked inside pollen grains) so they aren’t the choosiest of breeders. But even among mammals, hybrids frequently occur in nature.

In languages, the boundary is not sex but mutual intelligibility. French is considered a different language from English because, as Steve Martin says, “those French have a different word for everything!” But just as with the biological species concept, this is a useful rule of thumb, rather than an absolute rule. Speakers of closely related languages, like Danish and Swedish, can learn to understand one another with some ease.

Species have subspecies, and languages have dialects. Both are closely related to geography and geographic isolation. Languages like English and Chinese contain “dialects” that may be as mutually unintelligible as pairs of “proper” languages. Because the distinction between a language and a dialect is to some extent political, a common saying among linguists is “A language is a dialect with an army and a navy.”

Similarly, the distinction between species and subspecies in biology is somewhat arbitrary. Baboons, for example, are a widespread group of monkeys, occurring through most of Africa, with one species (Hamadryas baboons) extending their range across the Red Sea into Saudi Arabia and Yemen. Even though baboons are among the most intensively studied nonhuman primates, no one seems to about how many different baboon species there are, and what they should be called. Some people consider all baboons to be subspecies of Papio hamadryas. Other people distinguish ten or more species: Guinea baboon, Hamadryas baboon, Hauglin’s baboon, Anubis baboon, “typical” yellow baboons, Ibean yellow baboon, Kinda baboon, grey-footed baboon, Transvaal chacma baboon, and Cape & desert chacma baboon.

Jolly, C. J. (2001). A proper study for mankind: Analogies from the papionin monkeys and their implications for human evolution. Yearbook of Physical Anthropology, Vol 44. C. Ruff. New York, Wiley-Liss, Inc. 44: 177-204.
Jolly, C. J. (2001). A proper study for mankind: Analogies from the papionin monkeys and their implications for human evolution. Yearbook of Physical Anthropology, Vol 44. C. Ruff. New York, Wiley-Liss, Inc. 44: 177-204.

Interbreeding occurs among all these different kinds of baboons where their ranges overlap, so from the point of view of the traditional biological species concept, they are different species. But calling them all subspecies of Papio hamadryas seems odd because Hamadryas baboons are the most distinctive baboons of all: the males have showy capes and tufted tails, and their societies have an unusual multi-level structure quite different from the usual troops of “savanna baboons.” Moreover, as more studies are conducted of other baboons, it has become clear that each of these species (or subspecies) differs from others. For example, Guinea baboons turn out to have a social system quite similar to that of Hamadryas baboons.

So languages are similar to species, and dialects are similar to subspecies. These categories refer to populations. Within populations, individuals vary greatly, both in their language use and in their genes.

Each individual speaker of a language has her own set of words and rules: an idiolect. My idiolect may be very similar to yours, or quite different, depending on our shared vocabulary, which may include technical terms specific to our work, and idiosyncratic speech habits (which my wife complains I have in abundance).

An idiolect is similar to an individual’s genome. Each individual is unique, but at the same time, each individual speaker of a language shares a broad set of words and rules with other speakers of that language (otherwise they wouldn’t be able to communicate – and wouldn’t be considered speakers of the same language).

Continuing the analogy down to the next level, words are similar to genes. Words and genes are both combinatorial, in that they consist of sequences of smaller units combined to make larger units: syllables and letters in words, codons and nucleotides in genes.

Words are made up of syllables. Some words are made of single syllabus, such as “dog,” “cat,” and “fish.” Longer words can be made by combining syllables: “dogfish,” “catfish.”

Similarly, genes are made up of a series of codons. Unlike syllables, which can be spelled with anywhere from one to six or more letters (“a,” “-ed”, “-ing”, “ouch,” “queue,” “smooch,”), codons are always spelled with three letters.

Spelling is easier in genetics than in linguistics, because while languages may use dozens of letters (e.g., 26 in English), all genes are spelled with only 4 letters: G, A, T, and C. These letters stand for the nucleotides Guanine, Adenine, Thymine, and Cytosine.

Words are generally much shorter than genes, however, Words usually have only a few syllables, whereas genes can contain hundreds or thousands of codons.

Each 3-letter codon is translated into an amino acid; these amino acids are in turn connected up together like cars in a train to make proteins. The whole business of making proteins is very complicated, and is perhaps roughly analogous with the translation of mental representations of words into physical phenomena, such as sounds produced by the vocal tract, or signs made with the hands in sign language, or words written on a page or typed on a screen.

Linguistics Genetics
Combinatorial level Example Example Combinatorial level
Letter A, B, C, D, E, F, G… A, C, G, T Nucleotide
Syllable Dog, cat, in-, un-,-ness CAT, TAG, DAT, DCG Codon
Word Dog, cat, catness, undoglike hemoglobin, melanin, lactase, amylase Gene
Idiolect My particular speech My particular genes Genome
Dialect Upper Midwest American English Homo sapiens sapiens Subspecies
Language English Homo sapiens Species
Family Germanic, Indo-european Hominins, Primates Clade

In addition to being combinatorial, words and genes resemble one another in that they are both products of descent with modification. This is the phrase that Darwin preferred to “evolution,” and is really more precise about what happens in evolution. The descent part means that words and genes both have histories and family trees. The modification part means that both words and genes gradually change over time, across generations.

Both words and genes can undergo small changes, “mutations,” in how they are spelled. Genes can change by as little as one nucleotide. Many such mutations are “silent,” that is, they don’t affect the amino acid sequence made by the gene, because the genetic code is redundant: there are only 20 amino acids, but 64 possible codons. So some amino acids can be spelled several different ways. The amino acid serine, for example, can be spelled TCA, TCC, TCG, or TCT.

Mutations can have a wide range of effects, from not changing gene function at all, to wrecking the gene entirely. Some mutations result in slight improvements.

Words also undergo mutations. Talking about mutations in words is a little tricky in that the letters we use to spell them have an imprecise relationship to the way they are actually pronounced. In linguistics, the actual speech sounds that make up words are called phones.

Thus, “water” is spelled the same way in Dutch and English, but is pronounced slightly differently. Even within English, “water” is pronounced differently by different speakers and dialects. In the American Midwest, “water” is pronounced something like “wah-dur,” whereas in some dialects in England it is pronounced more like “wah-tuh.”

But both words and genes are robust to these small changes. They still work when altered just a little bit – which allows them to evolve.

Words and genes both accumulate small changes over time. These changes tend to cluster geographically. People who live near one another for many generations tend to speak the same language and dialect, and also tend to have more similar genes than people who live further away.

So what does all this have to do with the argument in biology about levels of selection?

In 1976, Richard Dawkins drew attention to the gene’s eye view of biology with his book, The Selfish Gene. Prior to this book, a widespread view in biology was that genes are something organisms use to accomplish certain goals. The heart pumps blood, the kidneys filter blood, and the genes store information and transmit it to the next generation. Dawkins, popularizing work by G. C. Williams and W. D. Hamilton and others, turned this view on its head: organisms are “survival machines” that genes use to make more copies of themselves. Dawkins argued that genes are ruthlessly selfish, because only those genes that succeed in getting copied are transmitted to the next generation.

Many people have objected to this view of evolution. Stephen Jay Gould, for example, argued that natural selection acts on individuals, rather than genes. Biologists including Edward. O. Wilson and David Sloan Wilson have argued that selection acts on multiple levels: genes, individuals, groups, perhaps even species. The debate continues with passionate advocates on each side.

In some ways, I think the debate is entirely sterile. Many people on both sides of the debate seem willing to agree that group selection is mathematically equivalent to kin selection. What really seems to feed the passion in this debate is the connotations that people have towards the idea of genes as “selfish” entities. Many people seem to have the impression that group selection is somehow kinder, gentler, and politically more left-leaning than gene-level selection. This view puzzles me, since plausible mechanisms of group selection are often quite nasty, such as intergroup hostility and warfare.

Genes are exotic entities, only recently discovered, and not fully understood even by professional biologists. Words, however, are familiar things that we all use all the time. So linguistic evolution might be easier to grasp for many of us than genetic evolution.

From a Darwinian perspective, a word is selfish in exactly the same way that a gene is. In both cases, versions that succeed in making more copies of themselves are the ones that persist over time.

Genes get themselves copied through reproduction. In species with sexual reproduction, they depend on their host finding a mate and (if there is any parental care) successfully rearing the resulting offspring.

Words get themselves copied in various ways. Vertical transmission is like biological reproduction, in that words are passed down from parent to child. Words differ from genes in that they are also easily passed among unrelated individuals: horizontal transmission. Horizontal transmission of genes does occur, especially in bacteria, but it is less common in complex multicellular creatures like ourselves.

Words vary among speakers, just as genes vary among individuals. Common words are shared by nearly every member of a language community, but there is still variation, among regions, social groups, interest groups, and individuals.

My idiolect, like my genome, is an ephemeral collection of words and rules. It will vanish when I die (apart from whatever words I have left behind in books and such – but even those will represent only a fraction of my actual idiolect, and will show the influence of co-authors, editors and such). My genome will also vanish when I die (parts of it will live on in my children, but all mixed up with my wife’s genes).

Words, however, have longer histories – as do genes. The word I use for H2O, “water,” comes from ancient roots. We see its cousins in words such as “Wasser” in German and the more distant cousin “voda” in Russian (whence the word “vodka,” “my dear little water”), and “uisge” in Scottish Gaelic (and its distilled descendant word in English, “whiskey”).

In language evolution, selection occurs mainly at the level of words. It is individual words that accumulate changes in their sounds and meanings. Words exist in a constant competition with other words for space in each individual’s vocabulary. Words come and go, depending on fashion, technology, and random drift.

The analogy is of course far from perfect and shouldn’t be pushed too far.

In fact, some linguists don’t like this analogy at all. In a 2014 blog post, linguist Asya Pereltsvaig complains:

words are not “just like genes” in that they are easily borrowed from language to language, even across family boundaries, are subject to conscious choice, and are not subject to natural selection.

The first point is true – sort of. The sort of genetic transmission that we are most familiar with is vertical (parent to offspring) rather than horizontal (from one unrelated individual to another). However, horizontal gene transfer turns out to be more important the people used to think.

Bacteria swap genes fairly frequently, such as when they share genes for resistance to antibiotics (like Deadheads swapping tapes of old Grateful Dead shows).

And according to one recent study, some 8% of the human genome originated in retroviruses.

So actually words and genes quite similar in this respect. Most genes, and most words, come from your parents, but some genes and words come from elsewhere, sometimes even quite unrelated sources.

The other claim, that words are not “subject to natural selection,” is also debatable. Pereltsvaig focuses attention the fact that word form is arbitrary.

As was noted by the “father of modern linguistics” Ferdinand de Saussure, the association of sound and meaning of a word is largely random: the sound of house is neither more appropriate to the concept nor better for the “survival of the fittest” than maison (French), dom (Russian), bayit (Hebrew), or iglu (Inuktitut)

It is true that the particular form of a word is basically arbitrary. But it is not true that selection has nothing to do with word form. Over time, long words that are frequently used get shortened. In both French and English, the invention of two-wheeled human-powered transportation required an accompanying new word (“vélocipède,” bicycle), which was subsequently shortened in both languages (“vélo,” bike). French teenagers commonly use “gar” for boy instead of the longer “garçon.” Words that are hard for native speakers to pronounce get changed to make pronunciation easier. Words whose meanings are transparently obvious to native speakers may generally catch on better than words whose meaning is opaque. For example, the term “earworm” (to describe a catchy tune that gets stuck in your ear) has a better chance of being understood, used, and catching on among English speakers than the original German word that it is translated from, “Ohrwurm“.

Pereltsvaig also claims, “words provide no adaptive advantage to people(s) who have them.”

But I disagree with this as well. Words are crucial to survival and reproductive success in human societies. Someone unable to use words at all would have tremendous difficulty holding a job or finding a mate. Using words well is essential, not just for those who write for a living, but also for anyone who talks with other people.

In some cases, correct understanding of a word could make the difference between life and death. One time at Gombe, an American colleague of mine thought she saw a hippo swimming in Lake Tanganyika. She grew alarmed, as several people were swimming nearby. Hippos may seem harmless but they enormous, terrifying beasts with huge sharp tusks (usually hidden inside their vast mouths). Hippos are often said to kill more people in Africa each year than crocodiles. To warn the swimmers, she shouted “Kifaru! Kifaru!” The Swahili-speaking swimmers just looked at her with a puzzled expression – since kifaru means rhinoceros in Swahili, and there was no risk whatsoever that there would be a rhino in the water. It turned out there wasn’t a kiboko (hippo) either, but if there had been, this linguistic mistake could have proved deadly.

The particular words we use tell others about our social status, our level of education, our sense of humor and style, and many other aspects that directly affect our reproductive success. Blurting out the wrong set of words can cost a person dearly (see, for example, James Watson, Tim Hunt, Donald Trump).

Looking at evolution from a gene’s eye view provides insights that simply aren’t available from other perspectives. Many aspects of biology don’t make any sense at all except from a gene’s eye view. The very existence of sex, for example. If selection occurred at the level of individuals, we should see individuals mainly making exact copies of themselves (clones). This sometimes happens in plants and animals, and is the norm for bacteria, but the widespread occurrence of sexual production is very difficult to explain, unless evolution is mainly about the replication of genes.

At the same time, words and genes both exist within incredibly complex systems in which the influence of any one word or gene may not be obvious. Just as each word contributes a tiny bit to each individual’s language output, each gene contributes a bit to each individual’s biological output. The total number of words that an individual speaker knows is estimated to be around 20,000 – 35,000. Coincidentally, this happens to be quite similar to the number of protein-coding genes in the human genome (around 20,000-25,000). Thus, in most cases, any single word or gene is likely to have only a small and subtle influence on an individual’s survival and reproductive success.

Words combine in complex ways to produce phrases, sentences, and longer things like poems, songs, articles and books. Gene products interact in complicated ways to produce living bodies and regulate the expression of other genes.

Both words and genes only make sense within the context of the complex system in which they exist. The French word “entrée” means something eaten at the start of a meal in French (the “entry” into the meal). When English speakers borrowed this word, they rather confusingly used it to refer to the main course of a meal. Similarly, the “meaning” of genes depends on the context in which the genes occur. In animals with red blood cells, the genes for hemoglobin make proteins that carry oxygen. But what would happen if these genes were inserted into a bloodless organism, such as a bacterium? Probably just an accumulation of protein that has no use whatsoever for the bacterium. (This may seem like a weirdly pointless experiment, but it has actually been done to produce and and study mammoth hemoglobin).

Additionally, just because words and genes are both “selfish,” in the sense that those that are better at getting copied are the ones that become most common in a given population, does not mean that they have to promote behavior that is selfish. Animals engage in all sorts of altruistic behavior, much of which is presumably the result of genes promoting altruism – that is in fact the central topic of The Selfish Gene.

For example, individual words might be “selfish,” in the sense that words with features that promote being copied get copied more often. But the words themselves don’t necessarily promote selfish behavior. For example, “Do unto others as you would have done unto you” is a combination of words that has been extremely successful in getting itself copied. Perhaps the great majority of the hundreds of millions of people who speak English have some version of this phrase stored in their memories; and other languages transmit equivalent versions of this phrase. The phrase is good at getting copied, but it advocates cooperative behavior, rather than selfish behavior. This is precisely why the phrase has been so successful. People who make an effort to follow the idea encoded in this phrase are likely more successful at navigating the complexities of village and urban life than people who are mean-spirited and selfish. “Selfish” words, like “selfish” genes, often promote cooperative behavior.

Language evolution and biological evolution both result from the accumulation of small changes at fundamental levels: words and genes. Words are “selfish” in exactly the same way as genes. Words and genes that have attributes that increase their likelihood of being reproduced become more common in the population. But neither words nor genes have goals, or minds, or emotions, or feelings of being selfish, altruistic, or anything else. They are just bits of information that happen to exist within copying systems. And just because these bits of information can be described as selfish doesn’t mean that they invariably code for selfish behavior.


Chimpanzee Violence and the Post-War Dream

Below is the text (more or less) from the TEDxUMN talk that I gave on 03 May 2015. A video of the talk is here.

I grew up in the Cold War.

The books, movies, and music were filled with fears of the end of the world.

One of my favorite albums was Pink Floyd’s The Final Cut: A Requiem for the Post-War Dream.

The album ended with the song: Two Suns in the Sunset.

The second sun being, of course, a thermonuclear explosion.

Looks like the human race is run.

War seemed inevitable. There was no way out.

But despite all the doom and gloom, it turned out these were actually the final years of the Cold War.

In 1989, the Berlin wall fell, and in 1991 the Soviet Union collapsed, not with a bang, but with a whimper.

St. Basil's Cathedral, Moscow. (August 1991)
St. Basil’s Cathedral, Moscow. (August 1991)









I was lucky enough to get a glimpse behind the Iron Curtain just as it was coming down.

I had a fellowship to study in England that came with money for summer travel in Europe.

I used that money to travel to Russia, then all the way to China on the Tran-Siberian Railroad. It turns out that this was the last summer that the Soviet Union existed.

And on the other side of Iron Curtain I found that people were pretty much just like us.

Soviet soldiers near Red Square, Moscow. (August 1991)
Soviet soldiers near Red Square, Moscow. (August 1991)







Walking around Moscow near Red Square, I saw Soviet soldiers – boys, really, about my age – playing around in a children’s park, taking pictures of each other.

This was an exciting time, with the Soviet Bloc and China opening up to the outside world.

It gave me hope that maybe war was something we can overcome.

I grew up worried about war but fascinated by apes.







As a kid, I saw Dian Fossey on TV with mountain gorillas and thought to myself: that’s what I want to be when I grow up.

It’s because of war, though, that I don’t study gorillas.

The mountain gorilla study is located in Rwanda, a tiny country in the heart of Africa. After college, when I wrote to the directors of the gorilla study asking if they needed research assistants, they wrote back saying they were closing camp down because Rwanda was descending into war.

The war continued for years, killing hundreds of thousands of people.

So instead of growing up to study gorillas, I study chimpanzees.

 You can’t always get what you want.

But if you try sometimes,

You might find,

You get what you need.

And what I needed was chimpanzees.

I needed chimpanzees because they are our closest living cousins.

Human family tree







Chimps and gorillas look a lot alike: hairy, knuckle-walking apes. The the two kinds of chimpanzees — “common chimpanzees” and bonobos — are more closely related to us than they are to gorillas.

And chimpanzees share a number of unusual traits in common with people.

They make and use tools – like this one here, who is using a stick to fish termites from their nest so she can eat them:

Golden fishing for termites.
Golden fishing for termites. (Photo by Michael Wilson)







Like humans, chimpanzees work in groups to hunter other animals.

And like humans, chimpanzees defend group territories, and sometimes gang up on members of other groups, attacking and killing their enemies.

It is this warlike behavior that I set out to study, looking for clues about how the origins and evolution of warfare in our own species.

So I went to study chimpanzees in Kibale Forest in western Uganda – much safer, I figured, than studying gorillas in war-torn Rwanda.

As it happened, though, the war in Rwanda spilled over into Congo, resulting in a huge war that eventually involved nine African nations and killed millions of people.

The first Congo war.
The first Congo war.









Kibale is just 30 miles from the border with Congo. On a clear day in Kibale you can see the snowcapped Ruwenzori Mountains that form that border.

And while the war raged in Congo, a Ugandan rebel group, the ADF, set up in those very mountains. Some of them were even rumored to be hiding in Kibale. The ADF bombed cafes and buses around Uganda, and attacked a school just 20 miles from us, burning 80 students alive.

At one point bandits attacked our village. They robbed and beat chimpanzee project field assistants, and shot and killed the brother of one of our employees.

And right around this time, one of the same field assistants who had been robbed found our chimpanzees beating on the freshly killed body of a male chimpanzee from another community.

The stranger’s body was covered in bites and other wounds, and his throat was torn out.

Why do chimpanzees do this?

Lots of other animals defend group territories, but in most species, they just chase their enemies away, rather than hunt them down and kill them. What’s going on?

Why do we kill?

One explanation for why we kill is the imbalance of power hypothesis, developed by Richard Wrangham and colleagues.

Behavioral ecologists think of aggression as the result of a cost-benefit calculation: animals use aggression as a strategy to get some benefit, when it looks like the benefit will be greater than the cost.

The benefits of aggression in chimpanzees are similar to those in other group territorial species: territory, food and mates.

But the costs of killing are low because of an unusual social structure that chimpanzees share with humans: fission fusion societies.

If we were gorillas, we would travel in a stable group all the time: a single male with his harem of females and kids.

But instead we live like chimpanzees: sometimes gathering in big groups, like we are now, and sometimes separating off into smaller groups.

For example, here are two neighboring territories: Blue and Red.







Each territory has 10 males.

There’s not much food at the moment in the Blue territory, so the Blue males are traveling in small parties, mainly ones and twos.

But there’s more food in the Red territory. They can travel in bigger parties, including this one with six males.

 These six males have safety in numbers, so they go on a border patrol.






 There they find a single blue male off by himself.






Bad luck for the blue male! The red males surround him, gang up on him, and kill him.







Now Blue only has 9 males.






With fewer males, Blue loses territory to Red. The Red males get the benefit of a larger territory with more food for themselves, their mates and their offspring.

The imbalance of power hypothesis makes some clear predictions.

For example:

Males should visit borders only when in larger groups.

Parties with more males should be more likely to approach strangers, to win fights, and to kill their enemies.

And winners should gain more territory.

I’ve spent much of the past 20 years testing these predictions.

I used playback experiments to test how males would respond to a stranger.

Donor and John setting up the playback equipment. (Photo by Becky Sun)








In each experiment, I played back a single pant-hoot call from a foreign male.

A pant-hoot sounds like this:


(And this is what a professor imitating a pant-hooting chimpanzee looks like:)

Pant-hoot demonstration.
Pant-hoot demonstration.




Hearing a single stranger calling in the distance had a big effect on the chimpanzees.

Rosa, Lope, Ipassa and Makoku looking towards an unexpected sound. (Photo by Becky Sun)








In parties with just one or two males, they looked towards the speaker, which was hidden some 300 m away. Sometimes they just stayed still, looking, but in about half the cases they slowly, cautiously walked towards the speaker.

In parties with three or more males, the response was totally different. They gave a loud “wraa!” response right after hearing the call, dropped down from their trees, and rapidly walked single file towards the speaker.

After each playback, we quickly packed up the speaker and carried it away, while one of us stayed at the speaker location to see what happened. Often that person was me.

I remember sitting there quietly in the undergrowth when suddenly I heard footsteps. I saw a line of males walking single file, their hair out, looking for someone to kill.

They glanced my way, but they weren’t interested in me. They knew who I was. They were looking for a stranger.

More recently, I’ve analyzed data from all the long-term study sites for chimpanzees.








What I’ve found is that killing is widespread, and occurs at most study sites.

In cases of intergroup killing, the attackers had an average 8:1 advantage over the defenders.

Analysis of long-term data has found that groups with more males expand their territory and obtain more food for self, mates, and offspring.

Just like chimpanzees, people are sensitive to the costs and benefits of aggression, and they prefer low cost fights: unfair fights that they are likely to win.

In human warfare, numbers matter, but even more important is weapons. Whenever people have developed a military advantage they have used it to conquer.

The Mongols, for example, swept across Eurasia with their fast horses and mounted archers.









But conquest, in humans and chimpanzees, is a zero sum game. Any benefit for my group is a loss for yours.

This is a risky game to play. About 12% of chimpanzees die from violence – that’s about out of eight.








The tables in this room seat about 8 people – so if were living in such a world, on average one person at each table would die from violence.

In human groups that live much like we did for most of our evolutionary history – as hunter gatherers and small scale tribal societies – the rate of death from violence is also about 12%.

For both chimpanzees and people, playing this zero sum game of group territorial behavior means a high risk of death by violence.

But unlike chimpanzees, people have found some ways out of the zero-sum trap and have learned to play positive-sum games.

This slide shows the risk of dying in battle from war in the 20th Century, for people worldwide:







The two big spikes are the First and Second World Wars.

What’s really striking about this graph is that there haven’t been any more really big spikes since 1945.

Nuclear weapons have raised cost of war so much that there have been no great-power wars in 70 years

People have – so far—avoided the horrible costs of direct nuclear exchange.

People are also sensitive to the benefits of peace, and these have increased over time, as the world has gotten more interconnected through trade.

The Trans-Siberian Railway is one of many links in this international trade. It connects Russia with China, and now with Europe as well.







I think back to my journey across Siberia. If I were a young male chimpanzee venturing so far from home, I would have been killed by the first group of foreign males I met.

But traveling deep into what had been enemy territory, I was never threatened. People can benefit from a stranger, if only by having someone to talk with, and share their vodka.

So what can chimpanzees tell us about war?








War is natural, but it is not inevitable.

People, like chimpanzees, are sensitive to both costs and benefits.

We can reduce war by increasing its costs, and by increasing the benefits of peace.

And what gives me hope is that the people I’ve met traveling around the world – they don’t want mutually assured destruction. They want the simple things listed in the Pink Floyd song about in the Post-war Dream:

A place to stay.

Enough to eat.

Somewhere old heroes shuffle safely down the street.

You can relax on both sides of the tracks

And maniacs don’t blow holes in bandsmen by remote control.

And everyone has recourse to the law.

And no one kills the children anymore.


All that jazz

So last week the Nielsen ratings for 2014 revealed that jazz has become the least popular major musical genre for adults, falling behind classical music. Jazz accounted for 2% of all albums sold in 2014, or about 5.2 million albums. Which is only a bit more than the 4.5 million copies of the Frozen soundtrack album sold that year.

Music evolves. Jazz has existed for just over a century, and during that time it evolved rapidly, giving birth to forms like Dixieland, big band swing, bebop, cool, bossa nova, free jazz, fusion, and acid jazz. Jazz dominated popular music for a few decades, the 1920s-1940s, but since then has lived mainly on the fringes.

If we think of genres as groups of animals, then Classical composers would be like Mesozoic dinosaurs. They were huge in their day, and we can still admire their articulated skeletons in museums or orchestra halls, but the world they ruled is gone. They were eclipsed in the 20th Century by the mammals: hot blooded popular forms like blues, jazz, country, rock, soul, and hip hop.

I have long thought of jazz as being marginal but still alive and kicking. Maybe like marsupial music. Marsupials don’t rule the world, but hey, they’ve got Australia, and they had South America pretty much to themselves for a long time, and opossums have even managed to spread into much of North America.

Has jazz become a monotreme music?
Has jazz become a monotreme music?

But now I fear that jazz has become more of a monotreme. Back in the Jurassic, egg-laying mammals were the latest thing. But now there are just two major groups of monotremes: one species of platypus and around four species of echidna, confined to Australia and New Guinea. Monotremes are amazing, and well worthy of study and conservation, but they are pretty much an evolutionary oxbow lake, far from the mainstream. For the most part most people don’t even think about them.

Whichever depressing analogy is most fitting, marsupial or monotreme, jazz is well on its way to being a museum music: curated by music departments and Jazz at Lincoln Center, subsidized by festivals where the headliners are often anyone but mainstream jazz musicians, but nearly extinct in the wild.

This makes me sad, because I love jazz, and have spent many years listening to it and trying to play it.

I remember seeing the jazz band play at Taylorville Junior High when I was still in grade school. The long row of saxophones, shiny and gold, with strange bends and twists in the horns, and the music they made — I was hooked. I started playing saxophone soon after, and have tried to make progress on that horn ever since.

In 1982, the average age of the jazz audience was 29. By 2008, the average age had increased to 46. Jazz used to be music for younger people, but now its audience is about the same age as the audience for classical music, opera and ballet. A demographic status that doesn’t bode well for the future of any of these genres.

Music is always changing. Today’s music doesn’t sound like yesterday’s music. Part of that is due to cumulative culture: today’s music builds on yesterday’s music, and is written in response to it. Music also evolves rapidly as technology for making music changes. Beethoven couldn’t write for saxophone because it hadn’t been invented yet. Gershwin, Ravel and Prokofiev did write for saxophone, but by then mainstream Classical music was already ossifying, too conservative to fully admit this new instrument into its ranks. So the saxophone found its home in popular music instead, where  it reigned supreme for a few decades, especially the 1930s and 1940s, and lingered on as a popular solo break instrument into the 1980s. But saxophones have been superseded in popular music by more recent technologies: electric guitars in the 1950s and 1960s, then synthesizers in the 1970s, and later sampling and other electronic tools.

Another reason for the high rate of evolution in music may be its role in sexual selection. Back in 1871, Darwin not only invented the term “sexual selection,” but gave music as a likely example of it in humans.

it appears probable that the progenitors of man, either the males or females or both sexes, before acquiring the power of expressing their mutual love in articulate language, endeavored to charm each other with musical notes and rhythm. (Darwin 1871: 880)

Darwin thus argued that song in humans had much the same function as song in birds: attracting mates.

Unlike many songbirds, in humans both males and females sing and make other forms of music. Some people have argued that this is evidence against a sexually selected origin of music in humans. But song need not be produced by only one sex to be a courtship signal. In a number of bird species, both sexes sing, and duetting is important for maintaining pair bonds. See, for example, the duets of the wonderfully named happy wrens.

Nonetheless, in humans there seems to be a bias for males to be performing for female audiences. Analyzing a sample of 1,800 jazz albums, 1,500 rock albums and 3,800 classical music works, Geoffrey Miller (2000) found that

males produced about ten times as much music as females, and their musical output peaked in young adulthood, around age thirty, near the time of peak mating effort and peak mating activity. This is almost identical to the age and sex profiles discovered by Daly and Wilson (1988) for homicides, which they took as evidence for sexual selection shaping propensities for violent sexual competitiveness. (Miller 2000: 354)

The standard rock band basically looks like a lek, which Wikipedia defines as “an aggregation of males that gather to engage in competitive displays that may entice visiting females who are surveying prospective partners for copulation.”

In his book My Appetite for Destruction, Steven Adler, the founding drummer of the rock band Guns N’ Roses, tells a story about how in high school football practice he played especially aggressively to impress a particular cheerleader on the sidelines. He goes on to say that music is much the same thing for him:

I don’t know why I’m wired this way, but there are very few things in life that really light me up. And nothing focuses me or gets me going like chasing tail. Money, fame, status, power . . . nothing comes close to the pursuit of pussy. It gives me an intensity that brings out the fiercest side of my competitive spirit.

When I was with the band I had to score the best snapper after a concert. I loved parading around backstage and at the after parties with the pick of the litter. So whether it’s trying to score by making touchdowns or playing in a band, I love the ladies. Primo poon: accept no substitutes. (Adler 2011: 13-14)

In a lek, the pressure is strong to sound new, innovative, and distinctive. And like Milton Babbitt said, “Nothing gets old faster than a new sound.” So the pressure continues to come up with new and distinctive sounds.

In contrast, the average jazz jam session is sort of an anti-lek: a group of mainly male musicians playing old style music, not for a crowd of screaming teenage girls, but for almost no audience at all.

But even if music has its evolutionary roots in courtship signals, the beauty and power of music transcend those roots. You don’t need to be courting to appreciate the intricacies of a Bach fugue or the cunning way the melody navigates the chord changes of All the Things You Are. The strange power of music — the way we perceive particular combinations of sounds as beautiful or ugly or joyous or despairing — works regardless of whether we are in a mating mood or not.

Psychologist Mihály Csíkszentmihályi argued that “people are happiest when they are in a state of flow— a state of concentration or complete absorption with the activity at hand and the situation.” He frequently mentions playing jazz as an example of this. And maybe this is why I keep coming back to jazz. It makes me happy.

And in some ways, this is an amazing time to be a jazz fan. YouTube has hundreds of hours of music and video. Growing up, I knew jazz mainly from what we played in jazz band and what I could hear on late night public radio, tapes from friends, and the occasional album. I had only the vaguest idea of what any of these musicians looked like. I didn’t even know Miles Davis was black until Aunt Lynn gave me an album (Workin’ & Steamin’) with his picture on it. Now anyone with an interest and an internet connection can watch videos of jazz greats playing. There are websites offering detailed advice about how to play jazz. And I’ve been meeting younger players who really know their stuff.  So maybe there is hope this particular branch of music will stay alive, growing and evolving, even if the mainstream has long since moved on.

Adler, S. (2011). My Appetite for Destruction: Sex & Drugs & Guns N’ Roses. New York, HarperCollins Publishers.

Darwin, C. (1871). The Descent of Man and Selection in Relation to Sex. New York, The Modern Library.

Miller, G. (2000). Evolution of human music through sexual selection. The Origins of Music. N. L. Wallin, B. Merker and S. Brown, MIT Press: 329-360.

Evolution and Warfare Workshop at NIMBioS

I’m very excited to announce that NIMBIoS, the National Institute for Mathematical and Biological Synthesis, will be hosting a workshop, “Evolutionary approaches to the understanding of decentralized warfare,” September 16-18, 2015, at the University of Tennessee, Knoxville.

I am organizing this workshop along with Luke Glowacki (Harvard University), Anna Simons (Naval Postgraduate School) and Sergey Gavrilets (University of Tennessee).

Objectives: Warfare is a widespread and arguably universal practice of human societies. While war’s origins continue to be debated, warfare has occurred in most historically documented societies, from hunter-gatherers to nation-states. Its prehistoric traces can be found in fortifications, weapons, mass graves, and skeletal trauma. Given that it is a major source of mortality, warfare has potentially acted as a powerful source of selection for both biological and cultural evolution. In a reprise of the past – and in contrast to force-on-force, hierarchically organized wars among great powers – conflict today takes a number of decentralized forms, from urban gang fights to livestock raids, and from clan warfare to leaderless resistance and terrorism. Suggestive parallels exist between current patterns of warfare and those that typified subsistence-level societies. Consequently, examining psychological mechanisms that evolved under ancestral warfare conditions may shed important light on what motivates individuals during modern decentralized wars and why people resort to violence in intergroup conflicts. Given the availability of data from contemporary societies and the great damage caused by violent conflict, advancing our understanding of such conflict is both tractable and important. In this workshop, we will begin working toward an integrated approach to the study of warfare under decentralized or only loosely controlled conditions, combining empirical data, evolutionary theory, and mathematical models. We envision developing working hypotheses to answer several key questions about between-group conflict in general, and the nature of ‘decentralized warfare’ in particular. These hypotheses will be informed by evolutionary theory using data from diverse conflict settings. Our hypotheses will be articulated in a framework amenable to formal modeling that will point the way toward a multi-level predictive understanding of warfare.

Descriptive flyer (PDF)

Application deadline: May 17, 2015. To apply CLICK HERE.
Participation in the workshop is by application only. Individuals with a strong interest in the topic are encouraged to apply, and successful applicants will be notified within two weeks of the application deadline. If needed, financial support for travel, meals, and lodging is available for workshop attendees.



So I got a call the other day to talk to a TV reporter about kissing. Valentine’s Day was coming up, and since it was also Darwin’s Birthday, it seemed fitting to talk about the evolution of this rather odd behavior. Moreover, even though my research focuses more on fighting and war than love and kisses, spending the last year living in France had me thinking about cultural variation in kissing.

People kiss a lot in France. Friends kiss each other when saying hello and when saying goodbye. Boys kiss girls, girls kiss girls, and boys kiss boys.  All this intimacy can make a shy person raised in the Upper Midwest feel quite awkward. And it presents all sorts of challenges. How well do you need to know someone before you kiss them? Do you actually touch the lips to the cheek, or just brush cheeks and kiss the air in their general direction? (Turns out its the latter.)

Though all this kissing might suggest an easy intimacy, in other ways the French are even more reserved than Americans. As French language and lifestyle expert Géraldine Lepère says, “Do not try to hug a French person. They will freeze.”

Adding to the challenge is that the number of kisses expected varies from region to region across France. In our area, Languedoc-Roussillon, three kisses were the norm.  But in other parts of France, the norm involves anywhere from one to five kisses. Greeting friends from those other regions was always a challenge. How many times do we kiss?

Geography of French kissing.
Geography of French kissing.









Thinking about all this cultural variation in greeting kisses made me wonder about the romantic kiss. Is it a human universal, or does romantic kissing show the sort of cultural variability that we see in greeting kisses? And what about kissing in our primate cousins?

Chimpanzees don’t have romantic kisses. But then they don’t really have romance. Mating is a quick business that last seven seconds or so, and the typical mating posture doesn’t bring the lips into close proximity. Females often scream and dart away after than mating rather than staying close to kiss and cuddle (though sometimes males do a bit of grooming of their partner in the afterglow).

Chimpanzees do kiss in other contexts, though, such as greeting and reassurance. Once at Lincoln Park Zoo in Chicago I saw two female chimpanzees engaged in a leisurely lip kiss that lasted at least ten minutes. But I don’t recall seeing anything like that in the wild.

Bonobos are reported to kiss more often, and to use their tongues when kissing. Frans de Waal writes, “French-kissing’ is totally absent in the chimpanzee, which engages in rather platonic kisses. This explains why a new zookeeper familiar with chimpanzees once accepted a kiss from a male bonobo. Was he taken aback when he suddenly felt the ape’s tongue in his mouth!” (de Waal, 1998: p. 103)

Unlike chimpanzees, bonobos frequently mate face to face, which would make romantic kissing more feasible. So perhaps romantic kissing in humans has something to do with our more bonobo-like mating postures.

In The Naked Ape, Desmond Morris suggested that kissing came from sharing food between mother and offspring. This is a classic example of ethological thinking, in which some puzzling, apparently useless behavior is interpreted as a ritualized version of an older, clearly functional behavior. But I’ve never liked this explanation. Partly I suppose because it’s a bit gross. But also, this isn’t something I’ve seen either people or other primates doing. I have seen human mothers pre-chew food for their children, but they transfer the food with their fingers, not their lips. And apart from Junior High stories about kissing couples sharing their chewing gum, food sharing doesn’t seem to play much role in romantic kissing in humans.

More recently, Evolutionary Psychologists have interpreted romantic kissing as a key component of mate selection in humans. By tasting a potential mate’s lips and saliva, kissers may be able to gain useful information about their health and perhaps even genetic quality and compatibility before taking any chances on actually combining their genetic material. One survey study of American college students found that women, more so than men, are reluctant to have sex with someone they haven’t kissed, and more likely to choose not to have sex with someone if they prove to be a bad kisser (Hughes et al., 2007). This makes sense given the sex differences in parental investment that are typical of mammals. Since women rather than men carry any resulting babies inside their bodies for months and then nurse them once they are born, women have a greater evolutionary interest in making sure they they screen potential mates for genetic quality.

Hughes et al. (2007) thus suggest that kissing is an evolved strategy, and argue that romantic kissing occurs in “over 90 percent of human cultures.” Kissing seems kind of a risky way to assess someone’s health, though. After all, if they turn out to be harboring some nasty infection, sharing their saliva is maybe not the best idea. Why not just a quick sniff of their breath instead?

Moreover, thinking about all the cultural variation in kissing in other contexts made me wonder whether romantic kissing was really so invariable.

Darwin, as usual, is way ahead of us here. In his 1872 book, The Expression of the Emotions in Man and Animals, he wrote that kissing was unknown in many non-European cultures:

We Europeans are so accustomed to kissing as a mark of affection, that it might be thought to be innate in mankind; but this is not the case. Steele was mistaken when he said “Nature was its author, and it began with the first courtship.” Jemmy Button, the Fuegian, told me that this practice was unknown in his land. It is equally unknown with the New Zealanders, Tahitians, Papuans, Australians, Somals of Africa, and the Esquimaux.

Darwin’s observation that romantic kissing is not a human universal is supported by a study that will be published in American Anthropologist later this year (Jankowiak et al., in press). This study examined 88 different cultures from the Human Relations Area Files, and also consulted with people working in various non-Western societies. They found that not only was romantic kissing not a human universal, it was only found in 40% of the cultures they examined. Strikingly, they found that romantic kissing was entirely absent in hunter-gatherers, the people whose societies are widely thought to most closely resemble the conditions in which our species has lived for most of our evolutionary history.

This finding seems to me an excellent example of the importance of good old fashioned Anthropology, in which the goal is to find document and explain human variation across the planet. If our picture of human behavior is based only on the behavior of our most convenient study subjects (e.g., American college students), we will come up with a badly distorted picture of our species.

In cultures with romantic kissing, pressing the lips clearly plays a big role in mate choice.  And the evolutionary logic for women being a bit more interested in the quality of kisses than men seems sound. But because kissing occurs only in a minority of human cultures, sex differences in preference for kissing must result from some more general mechanisms, rather than having evolved as part of a specific mental module for smooching.

Works cited:

Darwin, C. (1872). The expression of the emotions in man and animals. London, Murray.

Hughes, S. M., M. A. Harrison and G. G. Gallup (2007). “Sex differences in romantic kissing among college students: An evolutionary perspective.” Evolutionary Psychology 5(3): 612-631.

Jankowiak, W. R., S. L. Volsche and J. R. Garcia (in press). “Is the Romantic/Sexual Kiss a Near Human Universal?” American Anthropologist.

Morris, D. (1967). The Naked Ape: A Zoologist’s Study of the Human Animal .Jonathan Cape.

de Waal, F. B. M. (1998). Bonobo: The Forgotten Ape, University of California Press.

Irven DeVore

On Tuesday, 23 September, I lectured to my Primate Ecology and Social Behavior class about how methods of measuring behavior have changed since the first pioneering studies in field primatology. As an example of the importance of methodology, I used baboon troop progressions, a controversy starring Irv DeVore. That night, I learned from Greg Laden that Irv had died that same day, a couple of weeks shy of his 80th birthday.

I first met Irv twenty years ago, when I visited Harvard as a prospective graduate student. He sat at the big desk in the corner office of the Peabody Museum, at the top of the stairs. The bathroom outside his office stank of cigarette smoke because that’s one of the few places in the building he could get away with smoking. Irv looked a bit like Colonel Sanders: white hair, mustache and goatee, a tall southern gentleman, wearing a khaki field vest like he had just gotten back from safari and hadn’t had time to change clothes. The books packing the tall bookshelves included classics that Irv had edited: Primate Behavior: Field Studies of Monkeys and Apes (1965), Man the Hunter (1968) and others. From the walls hung artifacts from Africa: bows and arrows, spears, wood carvings.

We talked about baboons. At the time, I was working for Jeanne Altmann, managing data for the Amboseli Baboon Project, and had spent about ten months at Mpala Research Camp in Kenya habituating baboons for a Kenyan PhD student, Philip Muruthi. Irv told me about his own days studying baboons in Kenya.

Starting in 1959, as a student of Sherwood Washburn, Irv studied baboons in Amboseli and Nairobi National Park. At the time, very few people had studied primates in the wild in any detail. This was the same year that George Schaller began his pioneering studies of mountain gorillas, and a year before Jane Goodall began studying chimpanzees at Gombe. As this figure shows, Irv started studying baboons right at the start of an exponential increase in hours devoted to field studies of primates:

Time devoted to field studies of primates (from Altman, 1965)
Time devoted to field studies of primates (from Altman, 1967)







When I first met Irv, I was mostly ignorant of the many disputes in the history of baboon studies. The example I used in class the other day, about baboon troop progressions, was something that I only learned about later. It’s little more than a footnote now in primate studies, and perhaps not worth dwelling on, but is something I keep coming back to, as an example of methodology, an illustration of how science works, and a point of departure for thinking of Irv’s long and influential career.

By the 1950s, anthropologists were beginning to take seriously the idea that humans had evolved in Africa. Raymond Dart had discovered the oldest known hominin fossil, Australopithecus africanus, in South Africa (Dart, 1925). In attempting to reconstruct the likely behavior of Australopithecus, Dart drew on what was then known about baboons, which were the most conspicuous primates living where the fossil had been found:  on the open plains on the edge of the Kalahari Desert. Dart knew that baboons sometimes hunted and ate meat, which he used to support his view of Australopithecus as having made the transition from “fruit-eating, forest-loving apes” to  “the sanguinary pursuits and carnivorous habits of proto-men” (Dart, 1953).

Washburn hit on the idea of studying baboon behavior while at the 1955 Pan-African Conference in Prehistory in Northern Rhodesia, with Raymond Dart and Louis Leakey. Primarily a comparative anatomist, Washburn had dissected many baboons, which were considered vermin and could be shot at will. But at the Victoria Falls Hotel, Washburn began actually watching live baboons, and found their behavior fascinating, and relevant for testing many ideas about human evolution (DeVore, 1992).

Back in his home base at the University of Chicago, Washburn recruited DeVore to study baboons. At the time, Irv was a grad student in cultural anthropology, with no formal training in animal behavior. As a pioneering researcher, though, Irv quickly became the expert on baboon behavior. He and Washburn published their findings widely, in Scientific American, in edited volumes about primate behavior and human evolution, and in a series of educational films and pamphlets.

One of the puzzles in human evolution was how our ancestors could have survived on open plains inhabited by dangerous carnivores such as lions and leopards. DeVore and Washburn saw baboon troop progressions as an adaptation to keeping safe in this hazardous environment:

Illustration of a baboon troop progression from Hall & Devore (1965)
Illustration of a baboon troop progression from Hall & DeVore (1965)

A baboon troop that is in or under trees seems to have no particular organization, but when the troop moves out onto the open plains, a clear order of progression appears. Out in front of the troop move the boldest troop members-the less dominant adult males and the older juvenile males . . . Following them are other members of the troop’s periphery, pregnant and estrus adult females and juveniles. Next, in the center, comes the nucleus of dominant adult males, females with infants, and young juveniles. The rear of the troop is a mirror image of its front, with adults and older juveniles following the nucleus and more adult males at the end. This order of progression is invariably followed when the troop is moving rapidly from one feeding area to another during the day, and to its sleeping trees at dusk . . . (DeVore & Washburn, 1963)

There was a clear adaptive logic to this organization:

The arrangement of the troop members when they are moving insures maximum protection for the infants and juveniles in the center of the troop. An approaching predator would first encounter the adult males on the troop’s periphery, and then the adult males in the center, before it could reach defenseless troop members in the center. (DeVore & Washburn, 1963)

This idea that baboon societies were geometrically organized for protection appealed to people and became widely cited. As late as 1997 or 1998, I found a textbook in an elementary school in rural Uganda that contained a description of baboons that must have been adapted directly from DeVore’s publications. It faithfully replicated claims about the baboon troop progression, illustrated with line drawings of baboons.

Irv soon moved on from baboons to study hunter-gatherers and work in various ways to bring evolutionary theory into the study of human behavior. In the meantime, other researchers began studying baboons, including Stuart and Jeanne Altmann, who began doing fieldwork in Amboseli in 1963, soon after Irv’s pioneering studies there. Stuart was a leader in the newly emerging field of primatology, having studied rhesus macaques on Cayo Santiago and howling monkeys in Panama. As a graduate student of E. O. Wilson at Harvard, Stuart was one of the first researchers to use the term “sociobiology,” which he used to describe his approach to studying rhesus monkeys on Cayo. In his 1962 paper on rhesus monkeys, Stuart lists Irv as one on of the visitors to Cayo, sometime around 1957-58, so Irv must have visited Cayo before his own first trip to Kenya. Irv studied baboons for a few years; the Altmanns worked together for decades, establishing a long-term project that continues to examine many different aspects of baboon behavior and ecology.

In the midst of documenting many aspects of baboon lives, Stuart made a concerted effort to study baboon progressions (Altmann, 1979). This passage from the methods section of his 1979 paper illustrates the meticulous observations he undertook to test the hypothesis that baboon movements represent an orderly geometry:

Baboons in progressions were censused at opportune times during the course of several projects. With experience, we learned to anticipate their route of progression. From a position ahead of and to the side of the anticipated route, we selected a line of sight that was as free as possible of obstructing vegetation. We picked out some small visual marker, such as a rock or the edge of a distant tree, that would clearly fix the line of sight or ‘counting point’. Then, as each individual in turn walked past this imaginary line, its age-sex class was recorded. Whenever two individuals were close together as they passed the counting point, the order was determined ‘horse race style’, i.e. depending on whose nares crossed first. If an individual turned back across the counting point, then crossed it a second time, it was counted as being in its second position. Whenever possible, individual identifications were made. . . .  During many of these censuses, a second observer not only confirmed observations but also continued to observe individuals that were inadequately observed by the primary observer, who remained with eyes fixed on the counting point so as not to miss the next individual. Observations were facilitated by using 7x, 35mm (or 10x, 50 mm) binoculars, propped in position so that the observer could keep continuous watch on the counting point. Data were usually dictated into a portable cassette recorder, thereby eliminating any need to look down to write. (Altmann 1979: 49-50)

Analyzing data recording during many such observations, Stuart found that baboon progressions were essentially random, rather than strictly ordered:

In none of the baboon groups that we have studied is there a fixed progression order, either by individual or by age-sex class. Indeed, we have seen members of virtually every age-sex at every place in the group, including adult females with small, clinging infants in the front and rear of the group. (Altmann, 1979: 51)

So, as it turns out, Irv’s initial hypothesis about the geometry of baboon troop progressions was wrong. Irv would later tell his class of 500 students that he had done it all wrong, that none of the methods he used then would pass muster today. But Irv was one of the first. He was proud of his baboon films, which he said were the  first wildlife films to use synchronized sound (rather than simply adding sound in later). These films served as many students’ first introduction to baboon behavior. He drew attention to baboons and other wild primates as important subjects for understanding human nature and evolution. He inspired and taught generations of students who followed, including many who would become major figures in primate studies, including John Fleagle, Peter Rodman, Sarah Hrdy,  Patricia Whitten, Jim Moore, Barbara Smuts, Karen Strier, and others.

Irv was my co-advisor for my first years in grad school, and though this formal role lasted only a year or two, I learned a great deal from him , especially while serving on the team of Teaching Fellows for his giant lecture course, Science B-29.

While Irv nurtured and inspired primatologists for his entire career, long before I met him he had switched his focus back to humans. Starting in the mid-1960s, he helped launch modern studies of hunter-gatherers, advising Richard Lee and a series of others in studies of the !Kung San, who as a result became the proto-typical hunter-gatherers. The !Kung exhibit on the ground floor of the Peabody Museum beautifully depicted the material culture and lifeways documented by this project, with video interviews describing the rapidly changing conditions of their lives in more recent years.

In the 1970s, Irv embraced and promoted sociobiology, mentoring pioneers in the field including Bob Trivers and Sarah Hrdy. In the 1980s he assisted at the birth  of evolutionary psychology, advising John Tooby and mentoring others who became leaders of this new field.

When I was a graduate student, writing up my thesis, Irv dropped by my office one day, and noticed a copy of Primate Behavior on my shelf. He asked, “What are you doing with that old thing?”

Perhaps it was false modesty, but he seemed genuinely surprised that anyone would consult his old tome. I think he felt keenly that his earliest work had been supplanted by the rapid progress of primatology.

His obituary in the New York Times states:

While true that he never wrote a groundbreaking book that lasted the ravages of time, he was most proud of his students and spent his life nurturing them, mentoring them (as long as that didn’t include actually writing the letter of recommendation) and forcing his wife to edit their theses.

Irv published a number of books and other works, but his  list of publications doesn’t come close to reflecting his intellectual influence.

For evolutionary anthropology, Irv DeVore played a role a little bit like that played by Socrates in Greek philosophy.

As far as we know, Socrates never wrote anything. Instead, Socrates served as a teacher, asking questions, probing minds, encouraging people to question received wisdom.

Socrates never held a university position, or taught students in a formal classroom. Irv was a professor at Harvard and regularly taught a class of 500. However, like Socrates, Irv was most influential in informal settings. In Plato’s dialogues, the main source of information we have about Socrates, we often see Socrates as a guest at dinner parties. Irv seems to have been most at home, and most influential, in the Simian Seminars, the informal meetings that took place a couple of times a month at his home.

By the time I started grad school, the Simian Seminars were mainly the stuff of legend. We saw Irv regularly, as a lecturer, in seminars, and at beer hour (where he complained about the bitter, hoppy microbrews that the grad students favored), but the heyday of the Simian Seminars seems to have been from the 1970s through the early 1990s. Sarah Hrdy writes about them here.

In Plato’s Republic, Socrates discusses philosophy with a gathering of young men. It’s basically a dinner party. The discussion begins with an exchange between Socrates and an old man, Cephalus, who, seeing the end of his life approaching, busies himself with making sacrifices to the gods, to make sure things go well for him in the afterlife. Cephalus is pious and conventional. The conversation really gets going only after Cephalus leaves to make more sacrifices to the gods.

The Simian Seminars seem to have been a place where old Cephalus was not invited: a safe zone from pieties and conventional thinking.

At Simian Seminars almost no idea or topic was too sensitive, too politically incorrect or too bawdy to be off limits. This openness was made possible by an atmosphere of mutual trust, respect, and affection, which was very deliberately cultivated by the DeVores. (Hrdy, 2005)

In The Republic, the main impiety committed by Socrates was to talk about Justice without reference to the gods. As Plato describes in another work, The Apology, in the end Socrates was tried and executed for impiety. Among his crimes: teaching the young that the planets were not gods but were instead made of stone. But while Socrates may have held materialist views in regards to the planets, he still talked frequently of gods, daemons, souls, and an ideal world, arguing that the material world we see around us is a mere shadow of a higher reality.

Irv promoted an even more profound impiety: a serious embrace of evolutionary thinking. Daniel Dennett describes evolution as “the universal acid” (Dennett, 1996). It cuts through everything. Irv saw this and embraced it, and encouraged his students and friends and colleagues to think hard about what an evolutionary understanding of human nature really means.

Unlike Socrates, Irv was never tried for thought crimes, or forced to drink hemlock. But he did attract critics and and controversy. In Primate Visions , Donna Haraway uses DeVore as her main example of “the bad old days” before primatologists took notice of female primates. The schools of thought that Irv championed, sociobiology and evolutionary psychology, have long attracted controversy, and have been criticized by some for having a sexist bias. At least some of this criticism seems to result from people focusing on the titles rather than the contents of books. For example, many people seem to think that Lee and DeVore’s 1968 book Man the Hunter is devoted to celebrating the macho side of human evolution. Those who have read the book, though, will know that the authors actually argued against some widely held male-centered views. For example, Lee and DeVore argued that hunter-gatherer societies are often not organized along lines of male kinship (in contrast to the prevailing view at the time). Although the book’s title emphasized the meat hunted by men, inside the book the authors emphasized the importance of plant foods, which were mainly collected by women.

Because Socrates wrote nothing that survives, we know about him only from what was written by others. His followers, Plato and Xenophon, depict Socrates as a paragon of virtue and intellect; the playwright Aristophanes depicts Socrates as a clown. Similarly, Irv is perhaps better known from the words of his disciples and detractors than from his own work. And while detractors depicted Irv as someone focused on alpha male baboons and hunting men, as a mentor Irv championed both his male and female students. In Plato’s dialogues, only men participated in the philosophical discussions with Socrates. In the 1970s, some 2300 years later, women were still often excluded from important discussions. As Sarah Hrdy describes, though, the Simian Seminars welcomed women from the very beginning:

For many graduate students, these gatherings were the core of an unbelievably heady education. The format was especially important for women students, who in those days would often have been excluded from post-seminar gatherings where men talked out the issues over a beer, somewhere else. (Hrdy, 2005)

Irv was a pioneer. He was not a master of collecting or analyzing large datasets. But he was a great story teller. As a lecturer, he held the attention of hundreds of undergraduates every semester for decades.  Students laughed at his jokes and remembered details of his stories for years to come. He inspired many people to go out and check his stories, to prove him right or wrong. Most importantly, his overall vision of how to answer questions about human nature is, I think, spot on. To understand human nature, we need to take evolutionary theory seriously. We need to approach the world with an open, critical and creative mind. We need to test hypotheses with empirical data, not just philosophical introspection. We need to pay particular attention to the behavior and ecology of our primate cousins, and to people living as hunter-gatherers. Evolutionary principles hold enormous promise for explaining the behavior of people everywhere and everywhen. And in a lifetime devoted to implementing this vision, Irv championed collaborative work, took chances on unconventional students and ideas, and was not afraid to admit when he was wrong.

Irv DeVore at his last lecture, 15 December 2000. (Photo by Randall Collura)
Irv DeVore at his last lecture for Science B-29, 15 December 2000. (Photo by Randall Collura)










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