Category Archives: Aggression

Fighting over Food

Why do chimpanzees get into fights with their neighbors? As we report in this month’s Animal Behaviour, one of the major reasons seems to be food.

Since the 1970s, researchers have known that male chimpanzees defend group territories, and that fights between groups can be deadly. But what triggers these fights? Do chimpanzees go looking for trouble? Do they get into fights over mates? Or do they fight over some other resource, such as food? And when they do meet the neighbors, what determines whether they fight or flee? Are they more likely to respond aggressively if they are defending mates, or young infants, or food? Or does strength in numbers matter more? We sought to answer these questions, using 15 years of data on social behavior and ecology.

These data come from the Kanyawara community of chimpanzees in Kibale National Park, Uganda, where I did my PhD dissertation research as a student of Richard Wrangham and Marc Hauser. For the past decade, I’ve been doing fieldwork in Tanzania instead of Uganda, but I’ve continued to collaborate with Richard and his team. Such collaboration is made easier now that the long-term data have been entered into an Access database, and the original datasheets are all scanned, making it a simple matter to consult the original records from anywhere with good internet access.

Working with these data brought back many vivid memories, such as the day I first saw chimpanzees in the wild, back in June 1996. I had come to Kibale to spend a summer doing pilot research. We hiked for hours in the forest to find the chimpanzees, following narrow trails up and down steep hills, stepping carefully along narrow logs lain across boggy patches in the valley bottoms. Everything looked green and wet. Towering rainforest trees hung with vines. Dense stands of wild ginger and other leafy tropical plants crowded the understory.

As we crept along a steep trail, an opening in the trees showed the misty green expanse of the valley below. At last, I caught my first fleeting glimpse of a chimpanzee – I think it was Stout, an adult male – as he crossed the trail. His long black hair glistened with rain as he knuckle-walked calmly but quickly through the forest, looking more like a gorilla than I had expected, having only seen chimpanzees in movies and zoos.

During my first weeks at Kanyawara, the chimps traveled in large parties with many males. I saw most members of the community, including old Lamy, with his crippled foot, new mothers Outamba and Tongo carrying their first infants, matriarch Lope and her family, including the gangly teenager Makoku and young Rosa, grey-bearded Stocky, tough young males Imoso and Johnny, and Big Brown, who was still the alpha male.

During my first few days in the field, the chimps hunted and killed a red colobus monkey, and had a brief, noisy, and (for me) completely confusing encounter with their neighbors, during which the stranger chimps came within sight of us, crashing through the underbrush, displaying at and running towards our chimps before running they turned and ran away. As it turns out, I had come just in time for the last weeks of Uvariopsis season.

Uvariopsis congensis is a small tree that grows in large groves in the understory of the forest. It tends to fruit synchronously, usually in May and June. The fruits are small and red, and look rather like fleshy red peanuts, with two or three seeds.

At Kanyawara, the Uvariopsis groves occur mainly in the southeast of the range, along the border with another chimp community, which has not been habituated. And it turns out that that these Uvariopsis groves are a key focus of intergroup competition.

Back when I was doing my dissertation work, the number of intergroup encounters that had been observed at Kanyawara was still too small for meaningful statistical analysis. But now, in the 15-year dataset, we have records of 120 intergroup encounters. As is typical for chimpanzees, most of these encounters were shouting matches rather than full-fledged fights – chimpanzees gave loud pant-hoots and waa-barks and other calls, challenging their neighbors, and then ran either towards or away from them. But when chimpanzees came close enough to see each other, they were always hostile. Two chimpanzees were killed, and several others badly injured.  We found that these encounters happened mainly when chimpanzees visited border areas, especially the southern border.

So why did males visit border areas in the first place? To find mates, when few females in their own community were receptive? To find neighbors to attack, whenever they could gather in big enough parties to have a good chance of beating the neighbors? Or to look for food?

To answer these questions, we needed to use multivariate statistics to consider all these factors at once: mates, party composition, and food. We knew that male chimpanzees were highly motivated to search for mates, and we had previously found that parties that visited the range periphery had more males, presumably because that provided safety in numbers. But we also suspected that food would be an important part of the answer.

Chimpanzees spend most of their time searching for food, eating food, or digesting food. Though chimpanzees eat a variety of things, including monkeys, honey, ants, termites, leaves and stems, they spend most of their time eating ripe fruit from trees. In a tropical forest, the availability of tree fruits varies in a complex way over space and time. Some trees occur in groves in particular areas, whereas others are scattered about the forest. Some tree species, like figs, may produce food throughout the year, but other species fruit synchronously, with a big crop occurring every one or two years. To test how food influences chimpanzee movements, we needed data on both where and when key foods were located.

We had lots of data on feeding behavior. But it could be that chimpanzees travel to different parts of their range for social reasons (such as looking for mates or checking on the neighbors), and just happen to eat whatever they find along the way. So we needed to test whether the feeding data reflected where food was actually located. We therefore examined data from vegetation plots, and confirmed that both feeding data and vegetation plot data agreed that certain tree species were more common in the north, while others were more common in the south. For key species, we also found a good correlation between feeding behavior and independent measures of whether a sample of those trees had fruit in a given month. Additionally, the strong correlation between feeding records and counts of seeds from dung samples gave us confidence that our data on feeding behavior provided a good measure of what chimps were actually eating.

So what did we find?

Males tended to stay closer to the range center, and were less likely to travel to the south, when they were with more sexually receptive females. Party composition also mattered: as we had found previously, chimps were more likely to visit dangerous border areas when in parties with many males. And as we suspected, food had a big impact on chimpanzee movements. They visited the southern border mainly when southern fruits were in season. One species in particular had a strong effect on encounter rate: Uvariopsis. Most of the intergroup encounters took place in the southeast, in or near the Uvariopsis groves, and encounters were more likely to occur on days when chimps spent more time eating Uvariopsis.

So chimpanzees at Kanyawara visited borders for various reasons, but food seemed especially important. In particular, a good crop of Uvariopsis attracts chimps from both sides of the border, resulting in a spike in the rate of intergroup encounters during Uvariopsis season.

When encounters did occur, though, we found that the response depended mainly on the number of adult males that were present. Whether they were with mates, infants, or food didn’t matter as much as whether they had enough males to put up a good fight. These results were very much in line with what we had previously found with the playback experiments.

So is food generally the main driver of intergroup competition in chimpanzees? I’m currently working on data from Gombe to test whether similar factors apply there. It seems likely that in addition to food, the relative power of communities is a key factor. An interesting case in point is just 12 km from Kanyawara: the Ngogo community, studied by John Mitani and David Watts. This is the biggest chimpanzee community ever studied, with about 150 members. These chimps live in a range about the same size as Kanyawara’s, but in higher quality forest, with a lot more food, and three times the chimpanzees. And a lot more violence. The Ngogo chimps frequently patrol their boundaries, and in a ten-year period, Ngogo males killed 21 of their neighbors.

While the Ngogo chimps were killing their neighbors and expanding their range, the Kanyawara chimps were losing territory to their powerful southern neighbors (a group of unhabituated chimpanzees whose range appears to be sandwiched between Ngogo and Kanyawara). By 2006, the Kanyawara range was less than half as big as it had been in 1998, and the southern chimps had pushed the boundary a full kilometer north. It may be that chimps in a powerful community, like Ngogo, are more likely to go looking for trouble, whereas chimps in a weak community, like Kanyawara, visit dangerous border areas only when the abundance of food there makes the risk worthwhile.

Evolution is not just for Democrats

Reading the news these days, one might get the impression that evolution is just for Democrats, not Republicans. For example, in a recent (23 August 2011) post for the Washington Post, Richard Dawkins calls Republican Governor of Texas a “fool” and an “ignoramus” for expressing some doubts about evolution, and implies that these labels apply to anyone voting Republican.  The next day (24 August 2011), Ann Coulter published her own post, calling Richard Dawkins “retarded” and trotting out a series of tired old arguments against evolution.

Coulter is just plain wrong on evolution. At the same time, though, Dawkins is wrong to disparage the political opinions of people who happen to vote Republican.

Coulter is wrong about evolution in many ways. For example, she claims that if “Darwin were able to come back today and peer through a modern microscope to see the inner workings of a cell, he would instantly abandon his own theory.” Darwin, however, spent many years peering through microscopes at the inner workings of barnacles, and it was the fascinating complexity of their anatomy that deepened his understanding of evolution. Modern understanding of the inner workings of cells has further deepened scientific appreciation for how evolution works. The patterns of DNA encoded within each living cell have confirmed Darwin’s insight that every living thing on earth is part of one big family, the Tree of Life.

The Tree of Life

Comparing the similarity of DNA sequences has revealed some interesting surprises – for example, humans and chimpanzees are closer kin than chimpanzees and gorillas, even though gorillas look basically like giant chimpanzees – but has also generally confirmed the big picture of the tree that would be expected from shared descent with modification: humans and chimps are twigs on the primate branch, sprouting from the mammalian limb, emerging from the great trunk of vertebrate life, which near the roots of the tree joins with other great trunks and side branches: fungi, plants, and a variety of different bacteria.

Similarly, Coulter brings out the old argument from probability theory, that “it is a mathematical impossibility, for example, that all 30 to 40 parts of the cell’s flagellum – forget the 200 parts of the cilum! – could all arise at once by random mutation.” But as Dawkins clearly explains in The Blind Watchmaker – which Coulter doesn’t seem to have read, or at least not understood – evolution doesn’t throw together everything at once. Evolution works with small gradual changes, building on what exists already. It would indeed be statistically highly improbable to throw even a small number of things together at random and have them work together at all, much less well. But evolution doesn’t do that. Instead, evolution blindly, mindlessly tinkers with what already exists, changing a little bit here and there at random, and then lets these different variants fight it out in the arena of natural selection.

Coulter has made a career of strident political writing, and while the tone of her piece may be more appealing to those who already agree with her than persuasive to her opponents, it is at least consistent with her genre. Richard Dawkins, however, is a scientist. Indeed, he is one of our clearest thinkers and writers on evolution. It is disappointing that he here conflates views on evolution – which he rightly calls a scientific fact – with views on politics – which are, after all, opinions.

We have abundant evidence from fossils, geology, genetics, molecular biology, physiology, development, biogeography, and numerous other fields of study that evolution has occurred and continues to occur all around us. In contrast, while political opinions bear some relation to facts, they nevertheless pertain mainly to matters about which people with intelligence, experience and expertise continue to debate vigorously. Political questions are generally much more complicated and harder to be sure of than questions in the natural sciences, and they often relate to values – what people care about – rather than things that can be objectively determined to be true or false. Many political questions concern economics – which is routinely insulted as “the dismal science” because economists have such a great diversity of opinions. And why is economic opinion diverse? Is it because economists are more stupid or quarrelsome than other academics? Or is it because economies are just incredibly complex and difficult to understand?

Contrary to what readers of Coulter and Dawkins might be led to believe, evolution is not just for Democrats. The scientific truth of evolution doesn’t depend on a person’s political affiliation. People with all sorts of different political views have made important contributions to evolutionary theory. The great population geneticist J.B.S. Haldane was an idealistic Marxist and from 1937 to1950 a member of the Communist Party. Haldane’s colleague Ronald Fisher, described by Dawkins as “the greatest biologist since Darwin,” was politically conservative. Nobody today much cares about Haldane’s or Fisher’s political views. It’s their scientific ideas that have survived the test of time.

Darwin’s own political views might be hard to categorize today, because political views change greatly over time. Darwin shared Lincoln’s exact birthday (February 12, 1809) and Lincoln’s abhorrence of slavery. Maybe, if Darwin had been American, he would have voted Republican. I don’t know. But we don’t remember Darwin for the stances he took on the pressing political issues of his day. We remember him for his idea of evolution by natural selection, which remains just as powerful today as it was 150 years ago, and will continue to be so 150 years from now, or 150 thousand years from how, when the political issues we care so much about today will long be forgotten.

Indeed, evolution by natural selection will necessarily occur wherever life exists in the universe. If intelligent beings exist on a planet orbiting, say, Alpha Centauri, we can be sure of two things: (i) life on their planet undergoes evolution by natural selection and (ii) the question of whether to vote Republican or Democrat will be entirely, er, alien to them.

Hyenas can count

A new study in press at Animal Behaviour shows that hyenas can count. This study builds on work done in other animals, including work that I did on chimpanzees, and finds similar results: animals that fight in groups don’t like to pick fights if they seem to be outnumbered.

Game theory predicts that animals should use numerical assessment when deciding whether to get into a fight with a rival group. You generally don’t want to fight you can’t win. I found this to be the case with chimpanzees, and other studies have found this to be the case for lions and howler monkeys too. Game theory predicts that hyenas should do this too.

To test this prediction, Sarah Benson-Amram and others on Kay Holekamp‘s research team at Michigan State University did playback experiments with hyenas at Masai Mara in Kenya. A write-up of this study in Nature discusses how a particularly nice feature of this study is the way they set up the experimental stimuli. Previous studies have simulated larger groups by playing back recordings of multiple individuals calling at once. This is, in fact, what often happens in the wild – members of groups of lions, chimpanzees, howler monkeys, wolves, hyenas and such often call at the same time, probably to announce to the world that they are in a big group, so watch out. But experimentally, this raises the question of whether the animals are responding to the number of individuals, or just the total amount of noise in the vocalization. This study very elegantly disentangles these variables by always playing three non-overlapping whoops in each playback. In the single-intruder playback, the three whoops are by one individual. In the three-intruder playback, the three whoops are by three different individuals. And on hearing these playbacks, the hyenas responded differently to whoops by different individuals. When they heard the same individual calling repeatedly, their vigilance response decreased. But when they heard a new individual calling, they looked longer at the speaker.

So for hyenas to respond differently to the different numbers of callers, they have to be keeping track of the different individuals that call. This is trickier than simply distinguishing between a single caller and a chorus of callers – but it makes sense that hyenas should be able to do this, since their livelihoods depend on defending group territories and keeping track of how many rivals they face, even if they’re not all calling at once.

This method has the happy byproduct of also demonstrating that hyenas can tell individuals apart from their calls. It makes sense that they should be able to do this – but it’s nice to have experimental support for this prediction.

Will the New Atheism Save us from Jihad?

In March 2009, Richard Dawkins gave a talk at the University of Minnesota on “The Purpose of Purpose.” I was eager to see him talk, as I greatly admire Dawkins’ writings on biology, and assign his work as readings for my classes. Most of his talk, though, turned out to be an attack on religion, with many references to 9/11. The main message seemed to be: religion is a menace to humanity, it motivates people to do horrible things to one another, and we would all be better off without it.

It was only when I saw this talk that I really understood how much the flurry of so-called New Atheist books – The End of Faith: Religion, Terror, and the Future of Reason by Sam Harris (2005), Breaking the Spell: Religion as a Natural Phenomenon by Daniel Dennett (2007); god is Not Great: How Religion Poisons Everything by Christopher Hitchens (2007), and Dawkins’s own book, The God Delusion (2008) – owed their inspiration to 9/11. Okay, so maybe I’m a little slow to catch on – but not being a religious person myself, reading these books seemed a bit like, er, preaching to the choir, so I haven’t done so yet. But the main point that Dawkins made, and what I suppose motivates these other books, is this: we were attacked by crazy religious fanatics, and the best way to fight back is to attack the root of the problem: belief in God. As Victor Stegnor (author of The New Atheism: Taking a Stand for Science and Reason (2009)) quips: “Science flies you to the moon. Religion flies you into buildings.”

So, with the 10th anniversary of 9/11 approaching, maybe this is a good time to ask the question: will the New Atheism save us from jihad? My guess is: it probably won’t. And why not?

Well, for one, the audience for these books – educated people in rich countries, especially the United States and Europe – doesn’t really include the people who want to fly planes into our buildings. The chances seem pretty slim that someone like Osama bin Laden would pick up The God Delusion, give it an open-minded read through, and end up saying, “Oh, well, I guess he’s right. There is no God and no eternal paradise waiting for martyrs, so I should really just give up the jihad.” Even if all the educated people in rich countries stopped believing in God tomorrow, there would still be a world full of people who believed fervently in their own Gods, and in the righteousness of their own struggles.

Second, it seems at best an incomplete explanation to say that religion is what inspired the 9/11 attackers, and the rest of Al Qaeda, and their hosts in Afghanistan, the Taliban. Yes, they are all Muslims – but so are about 1.5 billion other people in the world. Why does this particular small group of people interpret Islam in such a way that it motivates them to attack us? What does Al Qaeda want?

According to Rohan Gunaratna, the author of Inside Al Qaeda (2002): “the ultimate aim is to reestablish the Caliphate—the empire of Islam’s early golden age—and thereby empower a formidable array of truly Islamic states to wage war on the United States and its allies.” 1

But what are they really fighting over? What was so great about the Caliphate? What did bin Laden and his allies think they would gain from its restoration?

There were a number of Caliphates. An especially impressive one, the Umayyad Caliphate, was  huge. By 750 AD, it stretched from Spain to Pakistan, and included much or all of Morocco, Algeria, Tunisa, Libya, Egypt, Israel, Jordan, Syria, Saudi Arabia, Yemen, Oman, the Gulf States, Iraq, Iran, Afghanistan, and others. Surely there’s a huge amount of historical pride and longing for this vast empire, and dreams of what could be done if all these lands united and used their oil wealth to achieve some grand unified aim.

And what would that aim be? I don’t pretend to know for sure. But I think we can get some clues from how the Taliban ruled when they were in power, and the laws they enforce where they have regained power. Many of the laws most harshly imposed by the Taliban had to do with restricting the freedom of women. For example, a decree from 1996 states:

“Women you should not step outside your residence. If you go outside the house you should not be like women who used to go with fashionable clothes wearing much cosmetics and appearing in front of every men before the coming of Islam.”

And it goes on and on like that. There are also decrees against kite flying, pigeon keeping, beard cutting, music, gambling and narcotics, but the main thing at stake seems to be the rights of women. Al Qaeda and the Taliban hate the West, not so much because the West is Christian, but because in the West women have rights and independence. Bin Laden had five or six wives, and fathered twenty to twenty-six children with them. The West represents a threat to traditional patriarchy and male power and control of women and their reproduction. Whether or not people in the West believe in God or not, Western values like equal rights for men and women represent a threat to the polygynous tribal patriarchy that greatly benefits high-ranking men like bin Laden.

It seems like a better bet for beating the jihad is to support the momentum of the Arab Spring. I don’t think the average person in the former lands of the Caliphate really wants the Caliphate back. That would just give all the power to the despots with their harems. Instead – if what the newspapers have reported about the protesters on the streets of Egypt and Libya and Syria is any indication – what the average person wants is the chance to get a job, to earn a decent living, to be able to afford to marry, have children, and live a quiet, peaceful life with freedom, dignity, and little risk of getting blown up by crazy people. According to The Atlantic, the rebels fighting in Libya love Western bands, including Pink Floyd. Maybe they share the postwar dream that Roger Waters sings about in the Pink Floyd song, The Gunner’s Dream:

A place to stay
Enough to eat
Somewhere old heroes shuffle safely down the street
Where you can speak out loud
About your doubts and fears
And what’s more no-one ever disappears
You never hear their standard issue kicking in your door.
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.

If basic political and economic reforms succeed in giving people a reasonable chance at such a life, I don’t think it will matter much what their particular religious views are. Nobody will bother with jihad.

Xenophobia and Immigration

A few years back, during a family visit to northern Minnesota, we came across the Hibbing Ethnic Festival. My brother-in-law, who lived in California, thought this was hilarious, as Hibbing is about 97% white.

“What ethic diversity?” he asked. “Swedes AND Norwegians?”

And sure enough, the Swedish, Norwegian, Finnish, Estonian, Latvian, Lithuanian, Russian, Welsh, Cornish, and other people that immigrated into Hibbing and other Iron Range towns were pretty much all pale-skinned Europeans. But they were not yet White. They were members of mutually hostile tribes. They spoke different languages, had different customs, different churches, and maintained deep suspicions towards one another.

Mom’s maternal grandparents were Swedish and Norwegian. At the time, this was a mixed marriage. Now we have a hard time remembering who was the Swede and who was the Norwegian. But at the time it was a big deal. And their daughter, my Grandma, once told me that in high school there was a boy who was allowed to come visit with her on the porch, but he was not allowed inside the house, because he was a Finn.

Nowadays, I think the Swedes and Norwegians and even the Finns get along just fine up on the Iron Range – and many of them are so intermarried through so many generations that ethnicity is just something to remember at the Ethnic Festival, if they still have it, when they need to decide who bakes the pasties, and who brings the lutefisk.

And we have such a universally favorable opinion now of the Norwegians – with their fjords and nice sweaters – that the news of the recent shooting just seemed unbelievable. We’ve grown used to Americans doing that sort of thing, but Norwegians?

The shooter, Anders Breivik, apparently thought that he was providing a wake-up call to save Norwegians and other Europeans from cultural and demographic suicide. According to his manifesto, he believes that Norway is being overrun with foreigners, many of them Muslim.

As part of an effort to understand why people can have such hostility to outsiders, Rhitu Chatterjee from PRI’s The World interviewed me, Frans de Waal, and Samuel Bowles about the evolutionary roots of xenophobia (fear of strangers). In this story, I get quoted mainly talking about the nasty side of chimpanzees, while the others get quoted talking about how nice bonobos and humans can be. Which I suppose is fine, since much of my work focuses on how and why chimpanzees can be so nasty to each other. But now that I have a blog, I can add a few of my own words about how and why people are different from chimpanzees.

Male chimpanzees spend their whole lives in the same community. They never leave their territory, which may cover 5 to 25 or more square kilometers (something like 2 to 10 square miles). They are perfectly capable of walking further than that, but in a world of chimpanzees, you can only go so far before running into another community’s territory.

Chimpanzees live in a zero-sum world. The only way they can get more stuff is by taking it from others. Their food supply depends on their territory. If they want more food, they have to take more territory from their neighbors. And if a male were to immigrate into another community, he would have nothing to offer the resident males. He would just be another competitor in the mating game – and even worse, he would be an unrelated competitor. If you’re a chimpanzee competing for mates against your father or brother or half-brother or cousin, it’s not so bad if you lose, because you share some of your genes with your kin, and those will get passed on. But losing to a stranger? That’s a total loss.

Humans, in contrast, have created a world that’s not zero-sum. When we meet strangers, we don’t have to knock them over the head and take their stuff to benefit from them. Instead, we can trade with them, to our mutual benefit. Even better, if we trade with someone this year instead of knocking him over the head, he might come back next year with more stuff that we want. We can also benefit from immigrants. When my great-great grandfather Anton came over from Sweden, the resident males in northern Minnesota didn’t gang up on him and kill him. Instead, they hired him to work in the iron mine. There were already lots of people living in the United States when Anton immigrated, but there weren’t enough of them willing to live up north and do the difficult, dangerous work of iron mining. So the mine owners, and the steel workers, and the people who used steel for their farm tools and anything else, all benefited from these immigrants. And it was dangerous – Anton died in the mine a month before his thirty-third birthday, when a block of stone fell on his head, leaving behind a young widow with a baby boy.

In the late 1800s, Norway and Sweden were poor countries with rapidly growing populations, and many people left for the US, where they and their descendents lost their tribal identities and became Americans. Now Norway and Sweden are rich, with slowly growing and rapidly aging populations. These countries need immigrants, and the immigrants are coming in from Eastern Europe, the Middle East and North Africa.

The United States has its share of ethnic conflict and resentment towards immigrants.  But it’s even trickier for the European countries. Being American depends on citizenship, not ethnicity. But in Europe, following the fall of empires and the rise of democracy, national boundaries were drawn around ethno-linguistic groups. It’s going to be a challenge for countries based mainly on old tribal boundaries to absorb these new immigrants. But with an aging, low fertility population, an increasing number of new immigrants will be needed to keep the European economies going. And as long as the countries to the south and east of Europe have growing populations and few job prospects at home, there will be lots of people knocking at the door.

But the amazing thing, from the perspective of a chimpanzee, is that people do this at all.