All posts by DaktaMaik

Chimpanzee Violence and the Post-War Dream

Here’s the text (more or less) from the TEDxUMN talk that I gave on 03 May 2015:

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.

http://eden.uktv.co.uk/gorilla-revisted-david-attenborough/gallery/photos-gorilla-revisted-david-attenborough/#4
http://eden.uktv.co.uk/gorilla-revisted-david-attenborough/gallery/photos-gorilla-revisted-david-attenborough/#4

 

 

 

 

 

 

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. http://en.wikipedia.org/wiki/First_Congo_War#/media/File:First_Congo_War_map_en.png
The first Congo war. http://en.wikipedia.org/wiki/First_Congo_War#/media/File:First_Congo_War_map_en.png

 

 

 

 

 

 

 

 

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.

Slide11

 

 

 

 

 

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.

 Slide12

 

 

 

 

 There they find a single blue male off by himself.

 Slide13

 

 

 

 

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

Slide14

 

 

 

 

 

Now Blue only has 9 males.

Slide15 

 

 

 

 

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.

Slide17
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.

Slide18
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.

Slide19

 

 

 

 

 

 

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.

Slide20
http://www.manchuarchery.org/photographs-mongolian-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.

Slide21

 

 

 

 

 

 

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:

Slide22

 

 

 

 

 

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.

Slide23

 

 

 

 

 

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?

Slide24

 

 

 

 

 

 

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?  https://aleonmiler.wordpress.com/2012/03/27/platypus-and-lady/
Has jazz become a monotreme music?
https://aleonmiler.wordpress.com/2012/03/27/platypus-and-lady/

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.

 

Kissing

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. http://all-that-is-interesting.com/map-of-french-kiss-customs
Geography of French kissing. http://all-that-is-interesting.com/map-of-french-kiss-customs

 

 

 

 

 

 

 

 

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, 1965)

 

 

 

 

 

 

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)

 

 

 

 

 

 

 

 

References

Altmann, S. A. (1962). “A field study of the sociobiology of rhesus monkeys, Macaca mulatta.” Ann N Y Acad Sci 102: 338-435.

Altmann, S. A., Ed. (1967). Social Communication among Primates. Midway reprints. Chicago, University of Chicago Press.

Altmann, S. A. (1979). “Baboon progressions: order or chaos? A study of of one-dimensional group geometry.” Animal Behaviour 27: 46-80.

Dart, R. A. (1953). “The predatory transition from ape to man.” International Anthropological and Linguistic Review 1(4): 201-218.

Dennett, D. C. (1996). Darwin’s Dangerous Idea: Evolution and the Meanings of Life. New York, Simon & Schuster.

DeVore, I. and S. L. Washburn (1963). “Baboon ecology and human evolution.” African Ecology and Human Evolution. C. F. Howell and F. Bourlière, Eds.. Chicago, Adline: 335-367.

DeVore, I. and S. L. Washburn (1992). “An interview with Sherwood Washburn.” Current Anthropology 33(4): 411-423.

Hall, K. R. L., & I. DeVore (1965). “Baboon social behavior.” Primate Behavior: Field Studies of Monkeys and Apes. I. DeVore, Ed. New York, London: 53-110.

Haraway, D. J. (1989). Primate Visions: Gender, Race, and Nature in the World of Modern Science. New York, Routledge.

Hrdy, S. B. (2005). “Milestones for Irv DeVore and the Simian Seminar.” Evolutionary Anthropology 14: 90-92.

Lee, R. and I. DeVore, Eds. (1968). Man the Hunter, Aldine Transaction.

Plato (1991). The Republic of Plato, Basic Books. Translated by Allan Bloom.

 

Human Impacts

Our recent paper on lethal aggression (Wilson et al., 2014) has attracted lots of attention, most of it positive. Not surprisingly, though, some critical responses have also emerged. Copied below is our response to one of these critiques.

John Horgan at Scientific American devoted a blog post to critiquing the paper — though this critique is not really focused on the paper, but on whether the paper’s findings support what Horgan calls the “deep roots theory of war.” Horgan later published a critique by Brian Ferguson, the main advocate of the Human Impacts Hypothesis. In introducing this critique, Horgan offered to post responses from any of the original paper’s authors. We therefore have written a response, which is now posted here. In case it might be useful, I’ve copied it here as well:

Human impacts are neither necessary nor sufficient to explain chimpanzee violence (or bonobo non-violence)

Michael L. Wilson, Christopher Boesch, Takeshi Furuichi, Ian C. Gilby, Chie Hashimoto, Catherine Hobaiter, Gottfried Hohmann, Kathelijne Koops, Tetsuro Matsuzawa, John C. Mitani, David Morgan, Martin N. Muller, Roger Mundry, Anne E. Pusey, Julia Riedel, Crickette Sanz, Anne M. Schel, Michel Waller, David P. Watts, Frances White, Roman M. Wittig, and Richard W. Wrangham[1]

In response to our recent paper (Wilson et al., 2014), Brian Ferguson (2014) critiques the methods we used to test whether chimpanzee violence is the result of human impacts. As Joan Silk notes in her commentary on our paper, “These results should finally put an end to the idea that lethal aggression in chimpanzees is a non-adaptive by-product of anthropogenic influences — but they will probably not be enough to convince everyone” (Silk, 2014: 321).

We expect that for the majority of primatologists, and among the wider community of animal behavior researchers, the results of our study are neither surprising nor controversial. But for those hostile to the idea that human violence relates in any way to biology or adaptive behavior, the Human Impacts Hypothesis (HIH) offers an out. Violence among our ape cousins is, in this view, the result of human contact, not the result of evolution favoring aggression as a strategy. The argument closely parallels Ferguson’s earlier argument that violence in tribal societies is mainly the result of contact with outsiders, especially European imperialists (Ferguson, 1990).

In contrast to some critics, Ferguson recognizes that “there is no question that chimpanzees have the capability to make war and have done so on occasion” (Ferguson, 2011: 249). Ferguson’s critiques thus represent a departure from what we might call the “strong anti-adaptationism” of previous proponents of the HIH. For example, Power (1991) argues that chimpanzee violence is a non-adaptive response to frustration caused by restrictive feeding methods at the first long-term study sites of chimpanzees, Gombe and Mahale. Ferguson embraces Power’s hypothesis that feeding chimpanzees made them more violent, but in contrast to Power, he argues that chimpanzee violence is mainly the result of resource competition, which is exacerbated by human activities such as feeding and deforestation. This argument differs little from arguments that behavioral ecologists regularly make to explain chimpanzee violence. For example, intercommunity violence in chimpanzees is strongly associated with competition over food resources. At Kanyawara, intercommunity encounters occurred most frequently when key food species were abundant in areas bordering neighboring communities (Wilson et al., 2012). Lethal aggression is strongly associated with territorial expansion at Ngogo (Mitani et al., 2010) and Gombe (Goodall, 1986), and by expanding territory chimpanzees increase the amount of food available to themselves, their mates and offspring (Williams et al., 2004; Pusey et al., 2005).

However, in his critique, Ferguson seems to conflate “resource competition” with “disturbance brought about by the actions of people.” Resource competition is not necessarily a “disturbance”, nor does it occur only as a consequence of “disturbance.” Instead, resource competition is a routine part of existence for living things. This is one of the central premises of evolution by natural selection, and evolutionary disciplines such as behavioral ecology. Ferguson therefore appears to agree with us that violence is an adaptive strategy for resource competition. And we agree that actions of people can sometimes affect resource competition in other animals, for example by adding a valuable, concentrated resource (Wrangham, 1974), or by removing key resources such as fruit trees, increasing competition for available land (Goodall, 1977). What we disagree on is whether the evidence indicates that human impacts are the main cause of chimpanzee violence.

Ferguson argues that “human impact must be approached in historical detail.” The 30 co-authors of our paper are deeply familiar with the historical details, with many of them having been involved in these long-term sites for decades. But historical awareness does not preclude a scientific approach. Clear predictions emerge from the hypothesis that human impacts cause chimpanzees to kill. We have sought to test those predictions systematically. We also appreciate that our study sites and study populations, and the human populations that now surround those sites, have complex histories that long pre-date our research projects, and that we should be aware of this fact despite the difficulties of reconstructing these histories. However, we are also concerned with history in another sense: the evolutionary history of chimpanzees. For the great majority of this history, chimpanzees and their immediate ancestors could not have been subject to “disturbance” of the kinds that Ferguson and other proponents of the HIH invoke.

When introducing Ferguson’s critique, John Horgan writes of confirmation bias, which is indeed a concern in any scientific endeavor. To counter this bias, scientists use tools such as collecting quantitative data and using statistical methods to test which models best explain the observed data. In our study, we sought to use methods that are objective and transparent, and which would provide well-substantiated answers, whether they agreed with our prior opinions or not.

In contrast, the “holistic” approach promoted by Ferguson is vulnerable to confirmation bias. Without clearly defining variables such as disturbance, and without using quantitative data and statistical methods designed to test whether a given set of results is likely given the available sample size, efforts to compare contrasting interpretations of a given set of data risk degenerating into cherry picking and special pleading.

Ferguson argues that “[t]he three measures Wilson et al. created to test for human impact are questionable.” However, he agrees in principle with each of these measures, and offers no quantifiable alternatives.

He states that our first measure, “artificial provisioning of food, is good, where it applies, though the impact of provisioning varies by how it is carried out and other conditions of food availability.” By this Ferguson presumably refers to the argument of Power (1991) that the “restricted” provisioning at Gombe and Mahale is what frustrated chimpanzees and (in Power’s view) fundamentally changed their behavior.

We do not dispute that providing food can change the behavior of chimpanzees and other animals. Wrangham (1974) found that at Gombe, chimpanzees and baboons were more aggressive in the feeding area than when foraging for natural foods away from the feeding area. What is clear from our study, however, is that provisioning is neither necessary nor sufficient for chimpanzees to kill.

We examined data on both chimpanzees (18 communities at 10 study sites) and bonobos (4 communities at 3 study sites). Of these sites, provisioning occurred at two chimpanzee sites (Gombe and Mahale) and one bonobo site (Wamba).

Evidence for lethal aggression has been found in seven of the of eight never-provisioned study sites (Budongo, Fongoli, Goualougo, Kalinzu, Kibale, Kyambura, Taï); the only exception is the small, isolated population at Bossou. Ferguson notes that “sites marked P for provisioning cluster (4 out of 7 cases) toward the high end of the killing distribution.” Fair enough, but the two highest rates of killing are for sites where chimpanzees were never provisioned. Moreover, at Mahale and Gombe, killings have continued to be observed long after provisioning ended (in 1987 and 2000, respectively). Killings by never-provisioned chimpanzees have also been reported at shorter-term study sites not included in our study, including Loango in Gabon (Boesch et al., 2007), as well as Conkouati-Douli National Park, Congo, where male wild-born, captive chimpanzees released into the wild were attacked by resident chimpanzees (Goossens et al., 2005).

Ferguson claims that “Provisioning’s statistical association with killing, however, is diluted by two other sites,” Mahale’s K-group and Wamba. “Diluted” is an odd choice of words here; if provisioning causes chimpanzees to become violent, then presumably every community provides relevant data, rather than dilution. Excluding K-group from the analysis would involve picking and choosing, excluding any data that doesn’t fit the expectation (in other words, guaranteeing confirmation bias).

Provisioning is thus clearly not necessary for chimpanzees to kill. Nor is it sufficient for killing to occur. Killings have been observed at both of the historically provisioned chimpanzee sites, but the observed and inferred killings by the Mitumba community at Gombe occurred only after provisioning ended there (Wilson et al., 2004). (We note, though, that one infanticide is suspected to have occurred at Mitumba during the time that Mitumba chimpanzees were provisioned (Pusey et al., 2008)).

Killings have not been observed at the provisioned bonobo site (Wamba). The one suspected bonobo killing took place at a non-provisioned site (Lomako). Ferguson notes that bonobos are a different species. Of course, this is true. But if provisioning causes chimpanzees to kill, why should it not cause other species to kill, especially closely related species?

Ferguson argues that Wamba should not be included in the analysis because bonobos are a different species. Fair enough; and indeed, in Table 3, we present results focused on just chimpanzees, excluding bonobos, and found that provisioning history did not explain variation in rates of killing among chimpanzee communities. But we also note that Ferguson has previously written that violence in chimpanzees is the result of social learning, proposing that bonobos would behave like chimpanzees if they experienced similar conditions (“What would happen if a bonobo were raised among chimpanzees or vice versa? I expect their behaviors would reflect the local custom” (Ferguson 2011: 255)). Following this line of logic seems to suggest to us that exposing bonobos to the same stimulus as chimpanzees (provisioned food) should result in a similar increase in aggressive behavior. But the one suspected case of killing by bonobos occurred at the never-provisioned site of Lomako, rather than the provisioned site of Wamba.

In our view, the much less frequent occurrence of violent aggression in bonobos compared to chimpanzees raises interesting questions about the evolution of non-violence as well as violence.

We note with interest, though, that Ferguson’s argument for provisioning is profoundly different from Power’s argument. Power argued that restricted provisioning fundamentally changed the behavior of chimpanzees at Gombe and Mahale, and that a wide range of chimpanzee behaviors reported by researchers there were the result of provisioning: male dominance hierarchies, despotic alpha males, possessive sexual behavior, closed membership of social groups, territorial behavior, female dispersal, hunting of monkeys, and intergroup killings. Studies of never-provisioned chimpanzees have found that all of these behaviors occur in the absence of provisioning. We can therefore reject the idea that chimpanzee behavior is fundamentally altered by provisioning. And indeed, instead of following Power’s argument that chimpanzee violence is maladaptive, Ferguson accepts that chimpanzee violence is an adaptive component of resource competition.

As a second measure of human impacts, we examined size of protected area. Ferguson notes that “some chimpanzee groups living within large protected areas have been heavily impacted.” Fair enough. That is why we conducted multivariate analyses considering several different variables. However, size of protected area is a measure that is readily quantified, and is likely important both for chimpanzee conservation and as a general measure of the degree to which chimpanzees have been affected by human activities. Like our other measures of human disturbance, however, size of the protected area did not have a consistent effect on rates of violence.

Our third measure of human impacts was an index of disturbance, based on a method developed by Naomi Bishop and colleagues for assessing the impacts of human activities on Hanuman langur monkeys in India (Bishop et al., 1981). Ferguson agrees that these measures “work well as a general index of over-all human impact,” but complains that “they do not work as predictors of intensified violence.” Similar complaints could be made of any effort to quantify human disturbance, because what exactly qualifies as disturbance is never clearly stated. However, it is worth pointing out that the disturbance index developed we used was originally developed to address a controversy over causes of infanticide (Bishop et al., 1981).

Importantly, for our disturbance rankings, each site director ranked their own site without prior knowledge of the rankings of other researchers. These rankings thus provide an independent estimate of disturbance made by the people who best know each of these sites.

Ferguson notes that Budongo has been exposed to various forms of lumber extraction, and other chimpanzee sites have experienced “islandization.” Fair enough. As primatologists actively involved in conservation efforts, we are deeply familiar with such issues at our sites. Capturing all of these different effects in a single variable, or a single index that combines several measures of disturbance (the approach we used), can never be wholly satisfactory. But we believe that the rankings that we did for our study do correlate reasonably well with the degree to which these different sites have been affected by humans. Goualougo is clearly the least affected chimpanzee site, and Bossou the most. Kanyawara, at the edge of Kibale National Park, has a higher disturbance rating than Ngogo, at the center of the park. We do not argue that our index is perfect, but we are not aware of a better one.

Ferguson points to many different possible impacts: provisioning, habitat clearance, timber extraction, hunting, and so on. Some of these could well have an effect on chimpanzee violence, by (for example) increasing the intensity of competition for resources. This is an adaptationist argument following standard theory in behavioral ecology, and as such, is an approach that we find reasonable. It is the fact that these are reasonable questions that motivated us to conduct our study. Given the possibility that human activities can affect rates of violence in chimpanzees, it is important to investigate the extent to which the observed patterns of violence reflect human impacts. This is what we have attempted to do, using data that are quantifiable, systematic, defined using the same criteria across study sites, and using a statistical approach that allows us to test predictions from multiple contrasting models. We found that human impacts did not explain the variation in rates of lethal aggression as well as other factors. Eastern chimpanzees killed more often than western chimpanzees, which killed more often than bonobos. Communities with more males and communities living in denser populations killed more frequently than communities with fewer males and sparser populations.

It is not at all clear why chimpanzees should react this way when exposed to humans, but not bonobos, baboons, or other species. For example, baboons have been studied at Gombe almost as long as chimpanzees and have been influenced by human activity. But they have not been observed to participate in coalitionary killing. What accounts for such differences between species when exposed to precisely the same human impacts? The absence of coalitionary killing in baboons makes sense from an evolutionary perspective (Wrangham, 1999), but is inexplicable from an anti-adaptationist perspective.

Moreover, chimpanzees and humans are far from the only species to engage in lethal aggression. Fatal fighting occurs widely among animals, and includes a broad range of examples, such as fatal fights among male spiders competing for mating opportunities (Leimar et al., 1991) and the killing and consumption of male spiders by female spiders, after (or sometimes during or even before) the males have mated (e.g., Andrade, 1996). Most such fatal fighting involves fights between individuals over a highly valuable resource. In contrast, coalitionary killing occurs in fewer species, and seems mainly limited to certain social insects, social carnivores such as wolves, lions and spotted hyenas, and a few primates, including humans and chimpanzees (Wrangham, 1999). Why coalitionary killing occurs in these species but not others is explicable, in principle, using the comparative method to develop testable hypotheses. An anti-adaptationist approach promises no such explanatory power.

Whether chimpanzee violence is adaptive or not, is a question for which we do not yet have a definitive answer. Answering this question in full requires information on reproduction and information on individual participation in violence, which is available for only a few sites and which has not yet been analyzed. Additionally, chimpanzees (like humans and other animals) may sometimes make mistakes, participating in killings that result in fitness (i.e. reproductive) costs. Whether a given behavioral strategy is adaptive depends on average effects of traits. Given these caveats, previous studies provide evidence in support of the view that chimpanzee violence provides fitness benefits to the attackers. Mitani et al. (2010) found that the intergroup killings by the Ngogo community were associated with substantial territorial expansion in the area where disproportionately many of the killings had taken place. Studies at Gombe provide evidence that larger territories provide important fitness benefits, including more food, as indicated by heavier individual body weights, controlling for age and reproductive condition (Pusey et al., 2005) and shorter inter-birth intervals for females (Williams et al., 2004). Males who enlarge their territory thus provide more food for their mates and offspring, enabling faster reproduction, and thus greater reproductive success for the aggressors.

In his critique, Ferguson mostly ignores the second focus of our paper: the pattern of attackers and victims. We found that most participants (92%) were male, as were most victims (73%). Most victims were members of other communities (63%). Intercommunity killings generally involved gang attacks, in which attackers outnumbered victims by a factor of 8:1. These patterns make sense when seen as adaptive strategies. Male chimpanzees defend group territories; eliminating members of rival communities enables males to increase the amount of food available to themselves, their mates, and offspring (Williams et al, 2004; Pusey et al., 2005; Mitani et al., 2010). Chimpanzees prefer to attack when the odds are in their favor (Wrangham 1999; Wilson et al., 2012). Viewing these behaviors solely as a non-adaptive response to human disturbance provides no insights into why attacks mainly involve males attacking members of other groups when the odds are in their favor.

The question of what, if anything, chimpanzee violence has to do with human warfare is one we did not address in our paper. We expect that among our 30 co-authors some diversity of opinion exists on this topic. We would all agree, though, that definitive claims about human behavior need to be based on data from humans.

Nonetheless, there are some important things we can learn from chimpanzee studies. Our study examines lethal aggression broadly, including infanticide and within-community violence. Despite this, the criticisms of Ferguson (as well as John Horgan’s earlier post) focus mainly on intercommunity killing, and its relevance to studies of human warfare. Ferguson, Horgan, and many others argue that warfare has a relatively recent origin (within the past 10,000 years (Ferguson, 2003)), due to some relatively new phenomenon, such as agriculture, or settled societies, or food storage, or property rights, or ideology, or new kinds of weapons. Chimpanzees have none of these things. They do sometimes use weapons (sticks and stones) but they don’t generally use them to kill each other. So the documentation of warlike behavior in chimpanzees shows that similar behavior could have occurred in humans long before the origin of agriculture and other evolutionarily recent innovations. It also raises the intriguing possibility that humans and chimpanzees share similar patterns of violence due to our shared evolutionary history; we may have inherited these patterns of behavior from our common ancestor.

As many have noted, however, and as we fully recognize, the existence of bonobos, with their much less violent societies, highlights the need to be cautious in how much we infer along these lines. It is possible that the lineages leading to humans and chimpanzees have both become more violent, or that the lineage leading to bonobos has become more peaceful over evolutionary time. We don’t yet know the answer to this question.

We heartily agree with Silk’s point that “Humans are not destined to be warlike because chimpanzees sometimes kill their neighbours” (Silk, 2014: 322). Variation in rates of warfare among countries today, and across historical time, clearly show that people can develop institutions and mechanisms that reduce the frequency and severity of warfare (Gat, 2006; Pinker, 2011). Chimpanzee communities also vary considerably in their rates of intercommunity violence. As we have found, this variation is better explained by differences among species, populations, and demography than by human impacts (Wilson et al., 2014).

References

Andrade, M. C. B. (1996). “Sexual selection for male sacrifice in the Australian redback spider.” Science 271(5245): 70-72.

Bishop, N., S. B. Hrdy, J. Teas and J. Moore (1981). “Measures of human influence in habitats of South Asian monkeys.” International Journal of Primatology 2(2): 153-167.

Boesch, C., J. Head, N. Tagg, M. Arandjelovic, L. Vigilant and M. M. Robbins (2007). “Fatal chimpanzee attack in Loango National Park, Gabon.” International Journal of Primatology 28: 1025-1034.

Ferguson, R. B. (1990). “Blood of the Leviathan: Western contact and warfare in Amazonia.” American Ethnologist 17(2): 237-257.

Ferguson, R. B. (2003). “The birth of war.” Natural History 112(6): 28-35.

Ferguson, R. B. (2011). Born to Live: Challenging Killer Myths. Origins of Altruism and Cooperation. R. W. Sussman and C. R. Cloninger: 249-270.

Ferguson, R. B. (2014). “Anthropologist Brian Ferguson challenges claim that chimp violence is adaptive.” Retrieved 19 September 2014, from http://blogs.scientificamerican.com/cross-check/2014/09/18/anthropologist-brian-ferguson-challenges-claim-that-chimp-violence-is-adaptive/.

Gat, A. (2006). War in Human Civilization. Oxford, Oxford University Press.

Goodall, J. (1977). “Infant killing and cannibalism in free-living chimpanzees.” Folia Primatol 22: 259-282.

Goodall, J. (1986). The Chimpanzees of Gombe: Patterns of Behavior. Cambridge, Massachusetts, Belknap Press.

Goossens, B., J. M. Setchell, E. Tchidongo, E. Dilambaka, C. Vidal, M. Ancrenaz and A. Jamart (2005). “Survival, interactions with wild conspecifics and reproduction in wild-born orphan chimpanzees following release into Conkouati-Douli National Park, Republic of Congo.” Biological Conservation 123: 461-475.

Leimar, O., S. Austad and M. Enquist (1991). “A test of the sequential assessment game: fighting in the bowl and doily spider Frontinella pyramitela.” Evolution 45(4): 862-874.

Mitani, J. C., D. P. Watts and S. J. Amsler (2010). “Lethal intergroup aggression leads to territorial expansion in wild chimpanzees.” Current Biology 20(12): R507-R508.

Pinker, S. (2011). The Better Angels of Our Nature: Why Violence Has Declined, Viking.

Power, M. (1991). The Egalitarians—Human and Chimpanzee: An Anthropological View of Social Organization. Cambridge, Cambridge University Press.

Pusey, A. E., G. W. Oehlert, J. M. Williams and J. Goodall (2005). “The influence of ecological and social factors on body mass of wild chimpanzees.” International Journal of Primatology 26: 3-31.

Pusey, A. E., C. Murray, W. R. Wallauer, M. L. Wilson, E. Wroblewski and J. Goodall (2008). “Severe aggression among female chimpanzees at Gombe National Park, Tanzania.” International Journal of Primatology 29(4): 949-973. get pdf

Silk, J. B. (2014). “Animal behaviour: The evolutionary roots of lethal conflict.” Nature 513(7518): 321-322.

Williams, J. M., G. Oehlert, J. Carlis and A. E. Pusey (2004). “Why do male chimpanzees defend a group range? Reassessing male territoriality.” Animal Behaviour 68(3): 523-532.

Wilson, M. L. (2012). Long-term studies of the Gombe chimpanzees. Long-term Field Studies of Primates. P. Kappeler and D. P. Watts. Heidelberg, Springer-Verlag: 357-384. get pdf

Wilson, M. L., C. Boesch, B. Fruth, T. Furuichi, I. C. Gilby, C. Hashimoto, C. Hobaiter, G. Hohman, N. Itoh, K. Koops, J. Lloyd, T. Matsuzawa, J. C. Mitani, D. C. Mjungu, D. Morgan, R. Mundry, M. N. Muller, M. Nakamura, J. D. Pruetz, A. E. Pusey, J. Riedel, C. Sanz, A. M. Schel, N. Simmons, M. Waller, D. P. Watts, F. J. White, R. M. Wittig, K. Zuberbühler and R. W. Wrangham (2014). “Lethal aggression in Pan is better explained by adaptive strategies than human impacts.” Nature 513: 414-417.

Wilson, M. L., S. M. Kahlenberg, M. T. Wells and R. W. Wrangham (2012). “Ecological and social factors affect the occurrence and outcomes of intergroup encounters in chimpanzees.” Animal Behaviour 83(1): 277-291. get pdf

Wilson, M. L., W. Wallauer and A. E. Pusey (2004). “New cases of intergroup violence among chimpanzees in Gombe National Park, Tanzania.” International Journal of Primatology 25(3): 523-549. get pdf

Wrangham, R. (1974). “Artificial feeding of chimpanzees and baboons in their natural habitat.” Animal Behaviour 22: 83-93.

Wrangham, R. W. (1999). “The evolution of coalitionary killing.” Yearbook of Physical Anthropology 42: 1-30.

[1] We invited all co-authors of our original paper to contribute to this response. All of those who responded to our invitation provided feedback and asked to be included as co-authors. Most (or perhaps all) of those who have not yet responded to this request are currently in the field with limited access to email. Not being included on this list, therefore, does not necessarily imply any disagreement with the contents of this response.

Chimpanzee violence

Are chimpanzees naturally violent? Or is chimpanzee violence the result of human interference, such as artificial feeding or habitat loss? Along with 29 co-authors, I  examine this question in a paper published this week in Nature.

Jane Goodall writes in her magnum opus, The Chimpanzees of Gombe:

Early field studies of chimpanzees (including my own) gave rise to the myth of the gentle, peace-loving ape. As more data on chimpanzee behavior have been collected over the years, this myth has gradually been dispelled. (Goodall 1986: 313)

Despite observations of violence in chimpanzees by Goodall and many others, a few  people still cling to the myth that chimpanzees are peace-loving apes at heart, moved to violence only by human impacts. This view was most fully developed by Margaret Power in her 1991 book, The Egalitarians—Human and Chimpanzee.

As far as I know, Power never studied chimpanzees in the wild. Instead, she based her arguments on reading the literature, especially Goodall’s early work, and also work by other people who had conducted shorter studies of chimpanzees at other sites, such as Vernon and Frankie Reynolds’ study of chimpanzees at Budongo Forest, Uganda, and Michael Ghiglieri’s study of chimpanzees at Ngogo, in Kibale Forest, also in Uganda.

Power distinguished “naturalistic” studies of chimpanzees from “provisioning” studies, in which chimpanzees were given food by researchers. This distinction follows a long tradition of researchers who have argued that Gombe chimpanzees were no longer truly “wild” after Goodall started feeding them bananas (e.g., Reynolds, 1975).

Power noted that in a 1974 paper,  Richard Wrangham showed that Gombe chimpanzees behaved more aggressively in “camp,” where researches fed them bananas,  than in the rest of their range, where they fed on naturally occurring foods. While Wrangham explained this change in behavior as a natural response to competing over an especially rich and concentrated source of food, Power developed a more elaborate argument based on psychological frustration theory, arguing that chimpanzee behavior was fundamentally changed by frustrations encountered at the feeding station.

Power argued that all sorts of chimpanzee behavior described by Goodall and colleagues, such as territorial behavior, dominance hierarchies, intense competition for mating opportunities, bullying by the alpha male, hunting of monkeys, and lethal aggression, were not natural behavior, but were instead the result of frustration caused by restrictive feeding of chimpanzees. She made the same arguments for Mahale, the study site established by Toshisada Nishida shortly after Goodall began her studies at Gombe. Nishida and his team used sugar cane to attract chimpanzees to an observation area. Power argued that this fundamentally changed their behavior, just as it had for Gombe chimpanzees. Only the earlier, “naturalistic” observations of  chimpanzees could be trusted. Power discounts all later observations from these sites, even though at both Gombe and Mahale, as chimpanzees became better habituated, researchers increasingly followed chimpanzees throughout their forest range, rather than focusing on observations at the feeding stations.

When Power published her book in 1991, chimpanzees had been studied at many different sites across Africa, but understanding of chimpanzee behavior in the wild was still very much dominated by studies from Gombe and Mahale. Nonetheless, new long-term studies were already underway at places including Taï Forest in Côte d’Ivoire and Kibale Forest in Uganda. These studies have continued, and new studies have been established at other sites. Researchers eventually stopped feeding chimpanzees at both Mahale and Gombe, and none of the newer study sites used artificial feeding to observe chimpanzees. Many of the new sites were in large, relatively undisturbed protected areas. And yet chimpanzees at all these sites demonstrated patterns of behavior that Power argued were the result of provisioning, including dominance hierarchies, bullying by alpha males, intense competition among males for mating opportunities, hunting of monkeys, and territorial behavior. These observations soundly refuted Power’s hypothesis that the behavior of provisioned chimpanzees was fundamentally different from that of unprovisioned chimpanzees.

Nonetheless, when I started studying chimpanzees in the mid-1990s, the number of detailed observations of lethal aggression in chimpanzees was still small. The most detailed accounts of killing were those from Gombe and Mahale. It seemed at the time reasonable to wonder whether those killings were the result of something unusual about those sites, such as the artificial feeding that occurred there. Or perhaps something else was responsible, such as the ecology of these sites, both located near the southeastern limits of the range of the species.

When I started graduate school, I was mainly interested  in language evolution. I wanted to do playback experiments with chimpanzees in order to test whether they had symbolic communication, like Dorothy Cheney and Robert Seyfarth had found with vervet monkeys. I went to Harvard to work with Marc Hauser, who had been a student of Cheney and Seyfarth, and Richard Wrangham, who had established a new long-term study of the Kanyawara community in Kibale.

Although my main focus was language evolution and communication, I was also inspired by two papers published in Current Anthropology:  “The human community as a primate society,” by Lars Rodseth, Richard Wrangham, and Barb Smuts, and “Intergroup aggression in chimpanzees and humans,” by Joe Manson and Richard Wrangham. The approach of these papers, seeking to explain human behavior through comparative study of other primates, seemed exactly the sort of thing we should be doing to gain a proper understanding of our species.

In 1996, I started my first field season at Kanyawara, doing a pilot study of playback experiments. These turned out to be the first successful playback experiments to wild chimpanzees — and they also ended up shifting my focus from language evolution to intergroup aggression.

We knew it would be hard to do playback experiments with chimpanzees. They are smart, and fast. We worried that playing soft calls at close range wouldn’t work easily, as they would find the speaker and catch on that something wasn’t right. So we needed to work with loud calls that would let us set up the speaker far away from the chimps. We also needed to focus on an experimental question that could be answered with relatively few trials, since we figured chimpanzees would habituate quickly to the experimental situation if we did the same thing over and over. So we settled on simulating intergroup events, playing a single pant-hoot call from a male stranger, using calls that John Mitani had recorded from chimpanzees at Mahale. This would enable us to test whether chimpanzees could assess the relative numbers of their opponents, much as Karen McComb, Craig Packer and Anne Pusey had recently shown with lions (McComb et al., 1994). As a result of choosing to do these particular experiments, I ended up shaping the rest of my dissertation research around questions of intergroup aggression.

In the fall after I had finished my first round of experiments at Kibale, Richard Wrangham and Dale Peterson published Demonic Males. This book inspired a closer look at intergroup aggression in chimpanzees. It also attracted criticism, particularly I think from people responding to the title of the book, rather than its contents. Among the more vocal critics have been Bob Sussman (1999, 2013) and Brian Ferguson (2011). Both Sussman and Ferguson have resurrected Margaret Power’s arguments that chimpanzee violence is not natural, but somehow the fault of humans.

At the same time, the evidence for chimpanzee violence continued to accumulate, not just at Gombe, but at sites across Africa. Many cases of violence have been reported from sites that were never provisioned. Critics such as Sussman and Ferguson have therefore shifted the focus away from provisioning and more towards other forms of disturbance: habitat loss, deaths from poaching and disease, and so forth.

In 2001, I finished my PhD and started working as a post-doc with Anne Pusey at the University of Minnesota. My main goal as a post-doc with Anne was to look at intergroup aggression data from Gombe, one of the very few sites where neighboring habituated communities could be studied. This provided a rare opportunity to examine intergroup aggression from both sides of the interaction.

Working at Gombe also increased my awareness of issues related to human impacts.  I ended up spending three years based at Gombe full-time, working for the Jane Goodall Institute. Conservation issues are important at every ape research site, but are particularly prominent at Gombe, given that it is a relatively small park exposed to substantial human impacts, especially deforestation outside the park. And throughout the time I have been working at Gombe, chimpanzees have, from time to time, attacked and killed one another.

In thinking about human impacts and chimpanzee violence, there are really two major issues to consider. One is whether human impacts, such as provisioning and habitat destruction, affect rates of violence. The other question is whether violence is mainly adaptive behavior or not. For example, Wrangham (1974) clearly showed that rates of aggression were higher at the feeding station than in the forest. But he argued this was a natural, adaptive response to a highly concentrated, high quality food source. Individuals who competed aggressively for bananas would get to feast on soft, easily digested fruits, rich in sugar and starch. Individuals who stayed out of the fray would go hungry, or have to go searching long distances in the forest for natural foods.

Likewise, during the decades when forests adjacent to Gombe were being cleared for farmland, it seems entirely plausible that this could lead to higher rates of violence, as chimpanzees retreated into the remaining protected area inside the park. If the number of chimpanzees in the area stayed the same, but the available habitat shrank, this could lead to increased aggression. In this case, though, increased aggression might well be a strategy by which individuals increased their reproductive success. Individuals that simply retreated, rather than defending their land, would be forced out of the good areas, while the aggressive victors would enjoy the spoils.

Critics such as Sussman and Ferguson seem mainly interested in arguing that aggressive behavior is maladaptive. They don’t like the idea that aggressors might benefit from violent behavior, and seem mainly worried about the consequences of such arguments. For example, if we argue that violent behavior is favored by natural selection, does that mean that we must then excuse violent behavior, and accept it as natural?

I think that such concerns are unjustified, however. Just because something is “natural” doesn’t mean it is desirable, or inevitable. Smallpox virus is natural, but deeply undesirable, and humans have intentionally and with great effort eradicated this virus. We have likewise made great strides towards reducing rates of warfare and other violence.

Nonetheless, whether chimpanzee violence is natural, or the result of human impacts, is an important question to get right. I have spent a number of years trying to answer it. I first presented a version of this study in 2004, in a talk at the International Society for Research on Aggression meetings in Santorini, Greece, titled: “Is chimpanzee intergroup violence the result of human disturbance?”

In this earlier effort, based mainly on the published literature, I didn’t find any strong link between human impacts and chimpanzee violence. By this time killings had been reported from several sites that had never been provisioned, including Ngogo and Kanyawara in Kibale Forest, Uganda, and Budongo, also in Uganda. But I had other things on my plate, and ended up putting this study on the back burner for several years.

It wasn’t until 2011 that I started working on the project again in earnest. Once I got started I realized that to really get a handle  on this question, published data wouldn’t be enough. I wanted to make sure that the data from each site was accurate, and that variables demographic and ranging data were all coded the same way. I wanted independent ratings of disturbance from each site. And I knew from my own experience that it can take years from the time that killings are observed to when detailed descriptions are written up and published. A study using just the published cases would result in a potentially severe underestimation of rates of violence. So I started contacting researchers at other sites and asked if they would be interested in participating. In the end the study included all the main long-term studies of chimpanzees and bonobos, and a long list of co-authors.

The main take home message of our study is that chimpanzee violence is natural behavior, not the result of human impacts. We have two main lines of evidence for this.

First, if we look across study sites, the degree of human impacts doesn’t explain the variation in rates of killing that we see. The site with the highest rate of killing, Ngogo, is in a forest with relatively low human impacts, and these chimpanzees were never artificially fed by researchers. In contrast, the site with the highest human disturbance rating, Bossou, is a site where killing has never been observed, despite many years of observation. Instead, overall killing rates are better explained by differences among species (chimpanzees kill more often than bonobos), and differences in demography (groups with more males, and that live at higher population densities, have more killing). Moreover, high population density appears to reflect good habitat quality, rather than human disturbance.

Second, if we look at the detailed patterns of who is killing whom, we see patterns that make sense from an evolutionary viewpoint, but which are hard to explain otherwise. Attackers did not kill at random. Instead, they mainly killed members of other groups (63% of killings). They mainly killed when they had an overwhelming numerical advantage (median 8:1 ratio of attackers to victims in intergroup killings). Attackers were much more often male than female (92% of participants in attacks) and they mainly killed males (73% of victims). They mainly killed when it was easy to kill victims, either because of a strong numerical advantage, or because the victim was weak (such as infants).

People often ask what the implications of this study are for human
behavior. I would say that definitive claims about human behavior need to be based on data from humans. But there are some important things we can learn from chimpanzee studies. One is that we can get much more detail on the contexts of killings in chimpanzees than is normally possible in human studies. We can watch them do everything in their daily lives, including killing — something we can’t do easily, ethically, or legally with humans. So we can collect lots of data that is useful for testing hypotheses about the biology of violence that apply to humans as well as other species. Another thing we have learned relates especially to the origins of warfare. Some people argue that warfare has a recent origin, due to some relatively new phenomenon, such as agriculture, or settled societies, or food storage, or property rights, or ideology, or new kinds of weapons, and so on. Chimpanzees have none of these things. They do sometimes use weapons (sticks and stones) but they don’t generally use them to kill each other. So the documentation of warlike behavior in chimpanzees shows that similar behavior could have occurred in humans long before the origin of agriculture and other evolutionarily recent innovations. It also raises the intriguing possibility that humans and chimpanzees share similar patterns of violence due to our shared evolutionary history; we may have inherited these patterns of behavior from our common ancestor.

The existence of bonobos, however, with their much less violent societies, highlights the need to be cautious in how much we infer along these lines. It is possible that the lineages leading to humans and chimpanzees have both become more violent, or that the lineage leading to bonobos has become more peaceful over evolutionary time. We don’t yet know the answer to this question.

 

References

Ferguson, R. B. (2011). “Born to Live: Challenging Killer Myths.” Origins of Altruism and Cooperation. R. W. Sussman and C. R. Cloninger, Eds. Springer New York. 36: 249-270.

Goodall, J. (1986). The Chimpanzees of Gombe: Patterns of Behavior. Cambridge, Massachusetts, Belknap Press.

Manson, J. H. and R. W. Wrangham (1991). “Intergroup aggression in chimpanzees and humans.” Current Anthropology 32(4): 369-390.

McComb, K., C. Packer and A. Pusey (1994). “Roaring and numerical assessment in contests between groups of female lions, Panthera leo.” Animal Behaviour 47: 379-387.

Power, M. (1991). The Egalitarians—Human and Chimpanzee: An Anthropological View of Social Organization. Cambridge, Cambridge University Press.

Reynolds, V. (1975). “How wild are Gombe chimpanzees.” Man 10(1): 123-125.

Rodseth, L., R. W. Wrangham, A. M. Harrigan and B. B. Smuts (1991). “The human community as a primate society.” Current Anthropology 32(3): 221-254.

Sussman, R. W. (1999). “The myth of man the hunter, man the killer and the evolution of human morality (evolutionary and religious perspectives on morality).” Zygon 34(3): 453-472.

Sussman, R. W. (2013). Why the legend of the killer ape never dies: The enduring power of cultural beliefs to distort our view of human nature. War, Peace, and Human Nature: The Convergence of Evolutionary and Cultural Views. D. P. Fry. Oxford, England, Oxford University Press: 97-111.

Wilson, M. L., R. W. Wrangham and A. E. Pusey (2004). “Is chimpanzee intergroup violence the result of human disturbance?” XVI World Meeting of the International Society for Research on Aggression, Fira, Santorini, Greece.

Wilson, M. L., C. Boesch, B. Fruth, T. Furuichi, I. C. Gilby, C. Hashimoto, C. Hobaiter, G. Hohman, N. Itoh, K. Koops, J. Lloyd, T. Matsuzawa, J. C. Mitani, D. C. Mjungu, D. Morgan, R. Mundry, M. N. Muller, M. Nakamura, J. D. Pruetz, A. E. Pusey, J. Riedel, C. Sanz, A. M. Schel, N. Simmons, M. Waller, D. P. Watts, F. J. White, R. M. Wittig, K. Zuberbühler and R. W. Wrangham (2014). “Lethal aggression in Pan is better explained by adaptive strategies than human impacts.” Nature 513: 414-417.

Wrangham, R. (1974). “Artificial feeding of chimpanzees and baboons in their natural habitat.” Animal Behaviour 22: 83-93.

Wrangham, R. W. and D. Peterson (1996). Demonic Males: Apes and the Origins of Human Violence. Boston, Houghton Mifflin.

Noah

Watching Darren Aronofsky’s film Noah makes me wonder: What gives this story such enduring appeal? It is scientifically implausible in all sorts of fascinating ways. The religious implications, if taken seriously, are deeply disturbing. And yet the story retains the mythic power to raise millions of dollars for its retelling, not just in Hollywood, but also in Kentucky.

In July, just a few months after the Noah film premiered, the state of Kentucky approved $18 million in tax breaks to support the building the Ark Encounter, a replica of Noah’s ark as interpreted by the Young Earth Creationist group, Answers in Genesis. Like its sister institution, the Creation Museum, the Ark Encounter will be a perverse sort of anti-museum, dedicated to ignorance and misinformation.  What is it about Noah’s story that inspires such dedication? Why would people of faith be willing to put such stake in a story for which there is no evidence whatsoever in history, archaeology, genetics, or biogeography, and which is so deeply implausible on the grounds of basic physics and planetary science?

As a kid, the Noah story was one of my favorite Bible stories – along with the Garden of Eden and Jonah and the Whale. These were among the few Bible stories that featured wild animals, rather than boring barnyard animals like sheep and goats. Sunday school handouts and children’s Bibles showed the parade of animals peacefully lining up to enter the ark. Curiously, people always seem to illustrate this story mainly with animals from Africa, rather than Mesopotamia, where Noah is usually thought to have lived.

Noah's Ark plate
Happy animals on the Ark.

For example, when my son was born, Mom gave us a set of Noah’s ark bowls and plates, which have been favorites of all our kids. This Ark has mostly African animals: a pair of giraffes looking out of the upper windows, a pair of African elephants, a pair of zebras, and a green bird that could plausibly be interpreted as an African green pigeon. Animals that could have lived in Mesopotamia include a bear, a pair of cats that seem meant to be leopards (or lynxes), two rabbits, a squirrel, and a pair of white geese. A pair of raccoons have also wandered in from North America.

Of course, if the Flood was global, than animals from all over the world should be there, but the African focus is interesting to me. Maybe Noah really lived at the foot of Mount Kilimanjaro, rather than Mount Ararat?

Growing up, Mom took us to church almost every Sunday. Dad came along to church twice each year, on Christmas and Easter, but otherwise spent Sunday mornings working on electronics in the basement or fixing things around the house. At our church near the corn and soybean fields at the edge of town, we sat in long wooden pews. Mom sang alto on the old Lutheran hymns, which the congregation sang in four-part harmony, accompanied by an electronic organ, which filled the sanctuary with magnificent sound. Pastor stood at the front of the church in his white robe, leading  the Psalms and liturgy in a clear high tenor, solemn melodies in strange minor modes. From Pastor’s sermons, I gained the impression that Martin Luther (or was it Martin Luther King?) had nailed his 95 theses to the door of our very church, which puzzled me greatly, as the door of our church was glass.

I grew up reading both the Bible and dinosaur books, with no inkling that there was any conflict between these two sets of information. The Bible stories were presented as factual, not just in Sunday school, but everywhere. Network television presented Biblical epics like The Greatest Story Ever Told and Jesus of Nazareth in much the same way that they presented mini-series like Roots and Holocaust: fictionalized presentations of real events. Movies depicted efforts to find Noah’s Ark on Mt. Ararat as a reasonable quest, which (based on tantalizing clues!) may have already succeeded.

I remember standing on the screen porch as a kid, five or six years old, singing a Bible school song about it raining 40 days and nights for the Flood. When I noticed Mom was in the room I stopped singing, embarrassed at having been heard, but puzzling over the lyrics. I asked Mom how many days it rained for the Flood, and she said, “Well, like the song says, I suppose.” That’s what it said in the Bible, so it must be true.

I read the Old Testament and was fascinated by the lists of the begats. You could connect these ages up and come up with an age of the Earth! I was pleased when I came across a giant family Bible with the dates right in there, based on Bishop Ussher’s calculations. The date of Creation, 4004 B.C., was a bit troubling, since I knew from my dinosaur books that the world was much older than that.

As I got older, I started noticing more and more the contrasts between different ways of looking at the world. Pastor one day mentioned in a sermon, “I will never understand how you can put green grass in a brown cow and get white milk.” He meant this as an illustration of the miraculous ways of the Creator. But this seemed to me an easy problem. Grass is green because it has chlorophyll. There’s no chlorophyll on the surface of cows, or in milk, so of course they’re not green. And cows are brown (or whatever other color) because of the pigments in their hairs. Why is milk white? I wasn’t sure at the time (maybe because of suspended fats?) but this seemed an answerable question to me, not a mystery.

I must have been in about sixth grade when I began to lose faith in the Ark. I was drawing a picture of it, and wanted to draw it to scale. I checked Genesis for the dimensions, and started thinking about how much room all the world’s animals would really need. That was the first time I remember doubting that the Ark really could have held all those animals. Tugging at that thread threatened to unravel the entire tapestry.

In Junior High, I attended confirmation class, and participated more actively in church, for varied reasons, including a growing obsession with the fantasy world of Dungeons and Dragons. My friend Tim and I were in the same confirmation class, and we often volunteered to serve as acolytes, which meant we got to wear medieval red robes and play with fire, lighting and extinguishing candles with the long-handled candle-lighter, which was satisfyingly like a medieval weapon.

Tim and I also attended Prayer Share meetings, where I had my first encounter with Young Earth Creationism. Our friend Amy, who went to a different church, insisted that before Noah’s flood, it didn’t rain. This was based on a passage in Genesis stating that Eden was watered with a mist. I argued with her that this couldn’t be. If a mist came and watered the land,  then the water would evaporate, form clouds, and it would rain. There’s nothing miraculous about rain; it just happens.  And yet Amy insisted that, based on this text, there was no rain before the Flood.

I was mystified by this sort of argument, yet as I learned on moving to Indiana, where Young Earth Creationists are thicker on the ground, this is a typical line of Creationist argument. And while I find the slipshod use of science in these arguments maddening, I have a certain amount of sympathy for Biblical literalists. They take the Bible seriously, and make an effort to follow through with the implications of that. If  the Bible is the Word of God, and every line is true, then Noah must have really lived and done all the things that the Bible says he did.

The Ark Encounter is the logical next step from the Creation Museum. If Darwin is a problem for your religion, then so are his predecessors, the geologists whose findings inspired him. In 1830, nearly thirty years before Darwin published the Origin of Species, Charles Lyell published his Principles of Geology, which persuasively argued that geological features are the result of natural processes acting locally over many years, rather than the outcome of a single global flood. Darwin carried the first volume of Lyell’s with him when he sailed around the world on the Beagle. When Lyell published the second volume of his book, Darwin eagerly picked it up in South America, where he collected fossils, examined geological formations, and shot lots of birds. These volumes profoundly affected Darwin’s views, describing a world where natural processes acting gradually over many millions of years create the features of the earth’s surface: mountains, hills, layered beds of sedimentary rock, uplifted and faulted and infiltrated by magma.

Lyell was a devout Christian, but he argued vigorously against using the Bible as a science book. Instead, he argued we should look to the Earth itself for evidence of the Earth’s history. Lyell’s arguments proved persuasive, leading the the founding of geology as a proper science, one which is central to an industrial civilization that is deeply dependent on good guidance for where to look for things in the ground that we need, such as iron, coal and oil.

Even though the last serious scientific debates about Flood Geology ended nearly two centuries ago, I can’t help myself from dwelling on other scientific implications of the Noah story. What would it take to make a world wide flood possible, for example? And what biological evidence would we see if such a flood had happened?

Maybe this comes from having a father who is an engineer. Growing up, conversations with Dad often ended up with him sketching diagrams on scraps of paper, working out calculations in scientific notation. So I find myself doing similar things, such trying to calculate just how much water would be needed for the Flood.

According to Genesis, the Flood covered the highest mountains. The highest mountain on the earth, Mount Everest, is 8.84 km high. The radius of the Earth is about 6,378 km. To calculate how much water you would need to cover the whole planet to the top of Everest, you just need to calculate two spheres: the volume of the Earth ((4/3)πr3 = (4/3)π(6,378)3=1.087 x 1012 km3), and the volume of a sphere of Earth plus Everest ((4/3)π(6,387) 3=1.091 x 1012 km3). Subtract the volume of the Earth from the volume of Earth plus Everest and you get about 4.5 x 109 km3.

Each cubic km has a million cubic meters, each of which weighs about 1,000 kg, so multiply the volume by a thousand million (109) and you get the total mass = 4.5 x 1021 kg. That’s a lot of water. Scientists estimate that the total mass of all water on the Earth’s surface today is 1.4 x 1021 kg. So Noah’s flood would require over 3 times as much water to be added to the Earth’s surface as is currently contained in all the world’s oceans, rivers and lakes. Where did all that water come from? And when the flood was over, where did it go?

The deeper you dig with this story, the more problems you find. For example, one of the clear predictions from the Noah story is that every population of large animals on the planet should show evidence of having passed through a very tight genetic bottleneck some 4,000 years ago. Human beings were reduced to a population of eight (Noah, his wife, their three sons, and their sons’ wives). Most other animals (except for the edible ones) had a surviving population of just two.

Every man on the planet therefore should be a direct descendant of Noah. Every man should therefore have a Y-chromosome that is nearly identical to Noah’s. Given Bishop Ussher’s timeline, the Great Flood occurred in 2,348 B.C., or some 4,362 years ago. If we assume human generation times of 25 years on average between the births of surviving females, then some 174.5 generations have passed since Noah.

(25 years is a bit conservative; the average time between mothers and daughters in a population of Polar Eskimos was 27 years, and 32 years between fathers and sons (Matsumura & Forster 2008)).

A recent study of mutation rate on the Y-chromosome examined men in China who descended from a common ancestor 13 generations ago (Xue et al., 2009). They found 4 differences between the Y-chromosomes of these men, and estimated the overall mutation rate to be 3 x 10-8 mutations per nucleotide per generation. There are about 1.02 x 107 nucleotides in the part of the Y-chromosome that they examined. The average man’s Y-chromosome should therefore differ from Noah’s by about (3 x 10-8 mutations per nucleotide per generation) (174.5 generations)(1.02 x 107 nucleotides) = 53 mutations. Which, out of 10 million nucleotides, isn’t very many. So most men on the planet should have a  Y-chromosome that is nearly identical to Noah’s. But geneticists find far more differences than this. One recent estimate of when the last common ancestor of all human Y-chromosomes (“genetic Adam”) lived yielded a date of 120,000 to 156,000 years ago. This is a lot older than 4,000 years.

And that’s just humans. For the Noah story to be true, every single animal lineage on the planet would have to show evidence of a catastrophically severe population bottleneck in recent history. And of course we see no such evidence.

Another testable prediction of the Noah story relates to biogeography. If the entire planet were populated by animals that Noah saved on the Ark, then we would expect to see some very striking patterns, based on the dispersal ability of animals. Suppose, as the tradition holds, that Noah’s Ark landed on or near Mt. Ararat in Armenia. Armenia should therefore be the center of global biodiversity. The rest of the world would be populated by animals gradually making their way from Armenia to the rest of the world over the past 4,000 years or so. Some animals, like many bats and birds, would be able to fly long distances and cross rivers and seas. We might therefore expect to see bats and birds worldwide. Other animals, such as many large land mammals, can walk long distances, but cannot cross major barriers such as rivers, seas, deserts, and large mountain chains. Consider elephants, for example. They can travel long distances, and we would expect them to travel far across Eurasia and across the Sinai Peninsula to Africa. Even elephants, though, might having trouble crossing the  Sahara, in which case the current abundance of elephants in sub-Saharan Africa poses a puzzle.

But that’s a small puzzle compared to the presence of large land mammals on any land mass not directly connected to Eurasia and Africa. That includes Indonesia, New Guinea, Australia, and the Americas. Bison, wolves, pumas, deer, llamas, and jaguars should be common in the area around Armenia, but they would never reach the Americas.

Many animals, especially smaller animals, and many plants, cannot disperse very far at all. Consider the sloth. Sloths, as their name implies, move slowly. They spend most of their time hanging from trees, eating and digesting leaves. Try to imagine Mr. and Mrs. three-toed sloth leaving the Ark, exploring the post-flood world of mud and dead trees. What would they eat? How would they travel? How would they ever get from Armenia to Central and South America?

As Darwin discovered on his worldwide voyage on the Beagle, the distribution of animal and plant species around the world only makes sense in light of evolution. Sloths live in South America because their ancestors evolved there many millions of years ago. In the glory days of the Giant Ground Sloths, sloths dispersed out of South America well into North America, but sloths have never spread beyond the Americas.

One could go on and on. It’s shooting fish in a barrel, really, or beating a dead horse, or whatever metaphor of futility you prefer. There are many pages of the Internet devoted to detailing these problems in mind-numbing detail, such as here, and here. This is all really overkill, since the Noah story is clearly just that: a story. And it’s a story that would make sense for a people whose history is entwined with the great river civilizations of Egypt and Mesopotamia, the land between the rivers. The discovery of a flood story in the Epic of Gilgamesh suggests that the Noah story is a close retelling of that older story (or a retelling of a common ancestor of the two tales).

And yet, the Noah story still has enormous broad appeal. Why is this so?

Leaving aside the scientific problems, the Noah story raises all sorts of questions about God. Why would an all-powerful deity do such a bad job of making people that he has to wipe them all out and start again? Was everyone on the planet entirely wicked except for Noah’s family? Surely there would have been some innocent people among the masses of the wicked: young children, if nobody else. If God was unhappy with some men, why didn’t he just zap them? Later in the Bible God repeatedly demonstrates His selective zapping ability: striking Onan dead, for example, or the first-born sons of the Egyptians but not Hebrews. Killing everyone on the planet seems deeply unfair, unworthy of a just God.

So given all this, why does this story still hold such appeal?

As a kid, I suppose I liked the story because it had animals. Noah is a kindly old zoo keeper. What a cool job he has! Looking after all those interesting animals! I’d like to have a boat full of tigers and gorillas. And it’s an adventure story: Noah and his family taking care of all those animals on a boat during a flood.

One thing I liked about Aronofsky’s Noah was that it brought out something hidden in the Sunday school version of the story: this is a horror story. It’s about death and destruction on a massive scale.

The Sunday school Noah is a righteous man, a skilled carpenter who does what God tells him to, looks after his family, and saves the animals. He is a hero of conservation biology. But Aronofsky brings out much that is deeply disturbing in Noah’s story. What kind of man would shut out the world from the Ark, saving his immediate family and some animals, but nobody else?

Peter Chatterway argues that here Aronofsky is following a long tradition in Jewish commentary. For example, Rabbi Shmuley Boteach argues that Noah is a deeply flawed figure:

Noah is not a hero in Jewish lore. The Bible says that Noah was a righteous man “in his generation.” He was only a righteous man compared to the others who were far worse than he.

Now, why wasn’t he righteous? Because righteousness is all about what you do for your fellow man. And Noah does NOTHING for his fellow man. He doesn’t care, he has no compassion. He executes God’s commandment to the letter. So when God says “I’m going to kill everybody,” Noah says, “will you save my skin? Oh, I get an Ark? Okay, fine.”

[Noah] failed in the greatest mission of all. He failed to protect human life. And failed to fight with God when he wanted to take human life. He refuses to wrestle with God. Noah is a fundamentalist. He’s a religious extremist. God says “everyone will die” and Noah says nothing. But this is not what God wants. God wants people with moxie! God wants people with spiritual audacity! He does not want the obedient man of belief. He wants the defiant man of faith.

It isn’t until Abraham, when God says “we have the rainbow and I promise not to destroy everyone, but I will destroy these two cities Sodom and Gomorah,” Abraham does something audacious. He says “will the judge of the entire Earth not practice justice?” He lifts his fists to heaven! He raises a cudgel to Heaven! This made him the first Jew. A Jew does not just accept a divine decree, he does not just bow his head in silent obedience.

The word “Islam” means “obedience before God” or “submission before God.” Soren Kierkegaard the great Danish theologian sums up Christianity as being a “leap of faith.”

Judaism has no leap of faith. “Israel” means “he who wrestles with God.” You see none of that in Noah. Neither in the Torah or in this film, so in that regard, this movie portrays this very well. No other religion does this, they would see this as heresy. It’s amazing, it’s breathtaking!

The scientific debate about Noah’s Flood ended nearly two centuries ago, with the birth of modern geology.  What we have learned since then about the deep history of the Earth is much more interesting and satisfying than the old myths. And yet, the myths still have a hold on our imagination. This may not be a bad thing. The Noah story can help promote an appreciation for our responsibility to life on earth: we must be good stewards of our planet. At the same time, understanding Noah to be a flawed man, a failure in his unquestioning obedience, might help make us better human beings.

 

References:

Matsumura, S. and P. Forster (2008). “Generation time and effective population size in Polar Eskimos.” Proceedings of the Royal Society B-Biological Sciences 275(1642): 1501-1508.

Xue, Y. L., Q. J. Wang, Q. Long, B. L. Ng, H. Swerdlow, J. Burton, C. Skuce, R. Taylor, Z. Abdellah, Y. L. Zhao, Asan, D. G. MacArthur, M. A. Quail, N. P. Carter, H. M. Yang and C. Tyler-Smith (2009). “Human Y Chromosome Base-Substitution Mutation Rate Measured by Direct Sequencing in a Deep-Rooting Pedigree.” Current Biology 19(17): 1453-1457.

Family Ties

Anton Johnson was born to a family of farmers in  Ärtemark Parish, Sweden in 1859. With his wife Christina he homesteaded a plot of forested land east of Ely, Minnesota. As I think Garrison Keillor has said of other Scandinavian migrants, they left their homeland, with its dark forests, thin rocky soil, cold weather, and short growing seasons, to find a better country. They traveled thousands of miles across the ocean and halfway across America until they reached Minnesota, where they settled down because it reminded them of home: dark forests, thin rocky soil, cold weather, and short growing seasons.

As it turns out, though, Anton got a job working underground in an iron mine, so it didn’t matter so much that the soils were poor and the weather was cold. This was in the early days of Ely’s rapid growth as a mining boom town. He and Christina had one child, Burt, born in 1890. Just over a year later, while Anton was working in the mine, a massive rock fell on his head and killed him. He was not quite 33 years old.

Christina remarried. Burt grew up, married a Norwegian girl, and had two daughters, who had their own families, whose members dispersed across the continent. I knew Burt as Dadda, my great-grandfather: a thin, straight, dignified old man, with thin white hair, thick, black, arched eyebrows, large ears and a long, thin face, serious but kind.

This August, nearly two dozen of his descendants and their families gathered together for a family reunion in a  cabin in the woods in northern Minnesota. In this group, there are some striking family resemblances. Some of my cousins look so much like their mothers that looking at them I feel I’ve become unstuck in time. There are many things that bind us together as a family, including shared memories of gathering in the north woods from time to time over the years. But I am also struck by how different we all are. We are family, but each person is a distinct individual, with different hopes and dreams, likes and dislikes, quirks and foibles. This is obvious, of course, even among siblings; each baby has its own temperament, and grows up to be a unique person.

Uncle Tim now lives out west, but owns the land that Anton and Christina homesteaded. One day we drove to the Ely area and spent two hours searching the woods for the property. Walking through the woods, slapping mosquitoes and gathering raspberries, it was easy to imagine what it must have looked like when those settlers first arrived.

The winters are cold and long. Grandma talked about how winter lasted seven months. I’ve been ice fishing up there in late April. Then once it warms up in the summer there are the mosquitoes, ticks and leeches. As soon as it gets warm enough to bare any skin there’s a crowd of bloodsuckers waiting to take a bite out of you. But the forests grow a bounty of raspberries and blueberries, and the lakes are full of fish. Loons cry their haunting call on the lakes, eagles fly overhead, and in the forests deer, wolves and bears are abundant.

Those northern Minnesota lakes and woods are almost enough to make me believe in ghosts. They vividly bring to mind memories of people who have passed on: sitting with Dadda at his breakfast nook while he explained the town of Virginia’s residential steam heating system; Nana lying in the nursing home bed with her bright blue eyes and wispy white hair;  Poppa scaling a bass after a long day fishing together; Mom orchestrating everyone in previous reunions, making sure that everyone was included and recognized and fed; and Grandma doing the hokey-pokey. I feel a connection to the land and the people. I can’t help wondering, though: if I stumbled back in time and met Anton and Christina in those woods, would we have much in common? Would we recognize each other as kin?

Kinship and lineage are powerful themes in the stories we tell. For example, in Dan Brown’s The Da Vinci Code, a central premise is that Jesus and Mary Magdalene had a child, thereby founding a lineage that continues unbroken to the present. Supposing for the moment that this were true, would people in this lineage be particularly special? Would they be more Christ-like (or Magdalene-like) than the average person?

From a religious point of view, this might be considered a silly question, of course; those who believe in the divinity of Jesus generally attribute this to Jesus having an extraordinary spirit in an ordinary human body. But in the fictional world of the Da Vinci Code, people devoted their lives to the principle that the lineage of Jesus was extra special, worthy of protection (or persecution). And even within the religious tradition, the writers of the Bible show great interest in lineages, describing in detail the generations connecting Jesus to the line of David, Abraham and Adam.

As an exercise focusing just on genetics and not spiritual matters, how many genes would a modern-day member of this lineage have in common with Jesus (or Mary)? We can estimate this using the coefficient of relatedness, r, defined as the probability that any two individuals share a given gene by common descent. (Most genes that we have are very similar to those of every other person on the planet, differing only in minor details, if at all, but the chance that any two genes are identical by descent is estimated by r.) Each sperm or egg that a person produces contains half of that person’s genome. Therefore each generation results in a halving of genetic relatedness: my daughter has half of my genes (r=0.5), and if she has a daughter, that child will have one fourth of my genes (r=0.25).

Estimating r for lots (n) of generations, assuming no inbreeding, r=1/(2n). Assuming human generation time to be about 25 years, about 80 generations have passed since the time of Jesus. The coefficient of relatedness between Jesus and any living descendants of his would thus be 1 over 1.2X1024, which is a really huge number – on the order of the total number of stars in the observable universe. One divided by such a huge number is effectively zero. The coefficient of relatedness between Jesus or Mary and any living descendant of theirs therefore would be r=0.0000000 (with zeros going on and on and on).

Of course, this is assuming that no inbreeding occurred. If (as is common in royal lineages) efforts were made to ensure marriages among members of the lineage, such as cousins, then r would be higher. But even so, with even a modest amount of marrying outside the lineage, the disruptive effects of sexual reproduction would rapidly erode much of the genetic similarity between the founders of the lineage and their remote descendants. Insofar as anything special about Jesus or Mary Magdalene was contained in the particular combinations of their genes, after a few generations of mixing and matching genes with people from other lineages, the descendants would have no more in common with Jesus or Mary than most other people in that population.

The same goes for any lineage. The “royal blood” of Queen Victoria, for example, is seven generations removed from the youngest heir to the throne, Prince George (r=1/27=0.0078). Thus, from a genetic point of view, Prince George is not particularly similar to Queen Victoria, despite being a relatively recent direct descendant of hers.

This calculation of r, though, doesn’t work for all genes. Some genes are passed down in packages rather than individually. We inherit our mitochondrial genome intact from our mothers. Mitochondrial genomes thus change only slowly, through the accumulation of mutations. In the same way, boys inherit their Y-chromosomes intact from their fathers. Prince George thus has the same Y-chromosome as his paternal grandfather Prince Charles.

Back in 2003, Tatiana Zerjal and colleagues published a paper showing that some 8% of men in Central Asia shared nearly identical versions of the Y-chromosome (Zerjal et al., 2003). Based on mutation rates and geographic patterns, they estimated that the family tree of this lineage originated in Mongolia roughly ~1,000 years ago. The most likely explanation of the wide spread of this chromosome was thus the historically well-attested reproductive success of Genghis Khan and his descendants.

There’s not very much on the Y-chromosome, though; just over 200 genes. Just because a man happens to have inherited a slightly mutated version of Genghis Khan’s Y-chromosome doesn’t mean that he shares anything more in common with Genghis Khan’s personality than any other man on the planet.

Personality and appearance both have strong genetic components, but because of sexual reproduction, similarities between lineage founders and descendants rapidly erode over time. So one might ask: given this erosion in similarity across the generations, why do we care so much about kinship and lineages? And more specifically, if there are only 200 or so functional genes on the Y-chromosome, why do patriarchs invest so much effort in ensuring that their particular Y-chromosome is perpetuated?

I suppose a major part of the answer must be that lineage survival is a pretty good proxy of fitness. If organisms are designed by natural selection to do whatever they can to promote the survival of their lineage, such organisms will leave more descendants, and thus more copies of their genes, than organisms that are indifferent to their lineage. If your lineage goes extinct, you won’t leave any copies of genes in the population. But if your lineage survives for two or three generations, and the number of individuals per generation grows rather than declines, then your genes have a good chance of surviving far into the future. Thus the particular satisfaction and happiness that grandparents and great-grandparents experience in seeing their descendants makes good evolutionary sense.

As for patriarchs, the focus on the patriline is less to do with the Y-chromosome itself, but with the greater potential variance in reproductive success between the sexes. The reproductive success of female mammals is limited by the number of babies they can have, whereas the reproductive success of male mammals is limited by their mating success. A Genghis Kahn or King David thus can have many more offspring than a Börte or Bathsheba.

Anton Johnson had just the one wife, though, rather than a harem, and he had only a single child before his life was cut short by a falling rock. Nonetheless, his lineage has carried on and grown.

The particular combinations of genes that Anton and Christina carried, though, have long since been mixed up with the genes of other lineages from varied parts of the world. That is, of course, the whole point of sexual reproduction. But whether due to genes, family experience, mate choice, or just the basic heritage of humanity, many members of this family do share an enjoyment in being outdoors, tramping around in the woods, and looking at living things.

White pine on Anton and Christina's homestead.
White pine on Anton and Christina’s homestead.

As we searched the woods, my son was the first to find the pipe in the ground that marked the southeast corner of the land that Anton and Christina homesteaded. After finding the corner marking, we could discern a cut line along the eastern boundary of the property: a straight path devoid of trees, brambled over in raspberries. Off the property, much of the land has been logged and is now covered with secondary growth: white-barked birches and poplar, thin trees crowded together, straining for the sky. But the family land has older growth, including a grand old white pine that already must have been a tall tree a century ago.

I don’t know what Anton Johnson was like as a person. If I could wander back to this same land 130 years ago, would I recognize any more kinship with him than with any of the other immigrant miners in the area? All the same, I still very much like the thought of him walking in the shadow of that same white pine, and perhaps admiring the flight of an eagle passing overhead.

 

Zerjal, T., Y. Xue, G. Bertorelle, R. S. Wells, W. Bao, S. Zhu, R. Qamar, Q. Ayub, A. Mohyuddin, S. Fu, P. Li, N. Yuldasheva, R. Ruzibakiev, J. Xu, Q. Shu, R. Du, H. Yang, M. E. Hurles, E. Robinson, T. Gerelsaikhan, B. Dashnyam, S. Q. Mehdi and C. Tyler-Smith (2003). “The genetic legacy of the Mongols.” American Journal of Human Genetics 72: 717-721.

Video Games

Do playing violent video games and watching violent television shows make people act violently? That was one of many questions discussed at the XXIst World Meeting of the International Society for Research on Aggression (ISRA), which met this July in Atlanta, Georgia.

ISRA was founded in 1972, “In the shadow of the Cold War, the Vietnam War, and social unrest throughout the United States.” Since that beginning, a goal of the society has been to use research to find ways to “reduce harmful aggression.” This is a goal that I share. But during the course of the meetings, I couldn’t help but wonder: after all these years of research, what have aggression researchers learned that has been of practical use to help people reduce harmful aggression in the real world?

Some of the ISRA talks focused on the neurobiology of aggression. This is a scientifically important topic, definitely worth pursuing. But I suppose that the practical benefits of such research are largely limited to a fairly narrow range of specific circumstances, such as developing drugs to help reduce violent behavior in people with certain mental illnesses. Will a better understanding of neurobiology really help to reduce rates of warfare, or civil strife, or violent crime?

Many of the other talks and posters focused on the social psychology of aggression. A particularly popular topic was the effect of violent media on aggressive behavior. The most prominent of these was the John Paul Scott Award talk by Professor Rowell Huesmann. This award “recognizes a lifetime or substantial contribution to aggression research,” so this is clearly a topic close to the heart of the society.

Professor Huesmann spoke on aggression and the media. He described aggression as a contagious disease, which is contracted through exposure to violence, whether real or fictional. Watching violence on television, or playing violent video games, gives children “scripts” about how they should act. Because people imitate, they imitate the violence they see on TV and experience in videogames and act aggressively in real life.

Professor Huesmann is an esteemed scholar with a long list of publications, honors and grants. His findings are based on studies with large sample sizes and careful statistics that show consistent, positive correlations between exposure to violent media and violent real life behavior. He also seemed like a very nice guy, earnestly devoted to reducing problems of violence in the real world.

Despite all this, I think the Media Violence Hypothesis doesn’t explain a great deal of violent behavior, even though it is intuitively appealing on several levels.

The argument that exposure to media violence causes real world violence has a certain plausibility to it. Kids imitate things they see on TV. In my high school, certain guys were constantly imitating pro wrestling moves with their buddies (though they always did so in comic slow motion). Teachers tell me they see their kids imitating moves they see on TV, such as Teenage Mutant Ninja Turtle attacks.

Another appealing part of the argument is that as video games become increasingly realistic, the violence becomes increasingly graphic and disturbing. Back in the 1990s, I played a game on a friend’s computer that must have been some version of Wolfenstein — a first person shooter that involved walking around a castle and shooting at Nazis. After playing for a while, I found the whole first person shooter aspect rather disturbing, particularly the blood pouring from the bullet wounds of the dead computer Nazis. I wouldn’t want my kids playing this game, and can imagine how spending many hours playing such games might affect a person.

So I can see how the Violent Media Hypothesis is appealing, especially to parents and educators. This hypothesis also suggests an obvious intervention: increased control over the media. If the hypothesis is true, then limiting violence in the media should provide strong practical benefits for reducing rates of violence in the real world — though of course this raises all sorts of problems for anyone interested in protecting First Amendment rights.

Despite the intuitive appeal of the hypothesis, though, and quite apart from concerns about media censorship, there are a number of reasons to think that that Media Violence Hypothesis doesn’t really hold up.

First of all, exposure to violent media isn’t a necessary precursor to violence. Neither ants nor chimpanzees nor any other animals require exposure to violent media to commit acts of violence. Numerous acts of violence occurred in human history, and prehistory, long before the invention of Pac-Man and Space Invaders.

This is, admittedly, a weak objection, given that the argument isn’t just about the media; it’s about the violence depicted in the media. Movies, TV and video games just provide novel means of displaying violence; new ways of spreading the contagion of violence. Long before violent media existed, people saw acts of violence being committed, which according to this hypothesis, would have resulted in further imitative acts of violence, which in turn would spawn yet more acts of violence.

There are, however, other reasons to think this hypothesis is implausible. One of these is my own personal experience. I don’t particularly seek out violent media. I have never played Grand Theft Auto or similar video games, and I don’t seek out slasher films. All the same, over a lifetime of watching TV and movies, and playing various kinds of games, I have been exposed to an enormous amount of simulated violence: murder, mayhem, rape, pillaging, decapitation, dismemberment, and all manner of horrible things. I’ve watched the entire population of the planet of Alderaan being destroyed by the Death Star. As a teenager playing Dungeons and Dragons, I fought countless virtual battles, throwing spears and whiskey bombs at orcs, hobgoblins and various other enemies. Playing Risk, I have commanded armies that slew many thousands of soldiers (though these were represented in the innocuous, non-bloody form of Roman numerals). I watched all six seasons of the Sopranos, in which many horrible murders were graphically depicted.

One would think that, according to the Media Violence Hypothesis, I would be deeply infected with the contagion of violence, and would have acted out these violent scripts repeatedly in my life. And yet, I have enjoyed a quite peaceful existence,  apart from a few rough wrestling bouts and fist fights in grade school.

I don’t think I’m unusual in this respect. Lots of people watch lots of violence on TV and movies, and experience simulated violence in video games, fantasy role playing games, and other forms, and yet have never committed a single act of violence.

Given all this, it would seem that violent media are neither necessary nor sufficient for violence to occur. Nor does it explain one of the most consistent findings in aggressive studies: men are consistently more violent than women. Men commit the great majority of homicides, and commit far more atrocities of war than women. If both sexes are routinely exposed to the same violent media, why should men be more violent than women?

Additionally, the Violent Media Hypothesis doesn’t  fit with patterns of violence over time, or across geographic space.

As Manuel Eisner described in his excellent plenary talk, rates of homicide have declined over the past thousand years or so in Europe. If the Media Violence Hypothesis were correct, we should see an enormous increase in violence following the invention and widespread dissemination of movies, television, and video games in the 20th Century. But what we see instead is a marked decrease in many different kinds of violence, including warfare and homicide. The horrors of WWI occurred when the film industry was still in its infancy. Television barely existed at the start of WWII. Since these cataclysmic events, the 20th Century has seen a steady decline in per capita rates of death from war, and decreases in homicide rates across Europe and North America. According to Eisner, there was an uptick in homicide in the 1960s through the early 1990s, but homicide rates declined thereafter, despite the release of a series of increasingly violent video games. (Grand Theft Auto, for example, was first released in 1997, when homicide rates in the US were on their way down.)

Considering geography, one would predict that the parts of the world most plagued by violence would be those most intensively saturated by television, films, internet and video games, such as the United States, Europe, and Japan. But while the US has higher rates of violence than Europe and Japan, its homicide rates are far below those of many countries where access to violent media is much more restricted. In many war-torn countries of Africa and the Middle East, per capita incomes are much lower and many people lack electricity, much less Xboxes.

So on a broad scale, the data don’t seem to support the Media Violence Hypothesis. It cannot explain why the latter half of the 20th Century was more peaceful than the first half, or why Japan is more peaceful than, say, Afghanistan.

The hypothesis seems even more doubtful from a theoretical perspective, especially when considered from an evolutionary perspective. In particular, why should evolution design people, or any other organism, to imitate acts of violence?

In evolutionary game theory, violence is a strategy that animals use to obtain key resources for survival and reproduction. If I am attacked by a predator, or a hostile member of my own species, I will fight back. Male chimpanzees fight for status, and for opportunities to mate with fertile females, and to defend and expand their territory.

Under many circumstances, imitating violent behavior would be maladaptive. For example, in chimpanzee societies, the alpha male frequently conducts charge displays, charging at, chasing, and sometimes hitting other community members. If a young, low-ranking male started imitating the alpha male by charging around and attacking other chimpanzees, he would get beat up in a hurry.

Professor Huesmann described studies showing that both Palestinian and Israeli children exposed to more media violence were more aggressive. Fair enough. But does anyone really think that the ongoing conflict between Israelis and Palestinians is the result of too much violent television? Or that Russia’s invasion of Crimea and ongoing support for separatists in Eastern Ukraine is the result of, say, Vladimir Putin watching too many Steven Seagal movies?

I would like to think that research on aggression can, and should, contribute to reducing harmful aggression. But I think that to find practical and effective solutions, we need to focus on the right level of analysis, guided by theoretically plausible hypotheses. Evolutionary theory provides critically important guidelines for what sorts of hypotheses are likely to be plausible. But a complete understanding of violent behavior also needs to look at a broad range of factors, including history, politics, and demography. A few disturbed people may be inspired to violent acts by violent video games, but it seems likely that the great majority of violent acts are best explained by conflicts over limited resources,  such as land, oil, and status.

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