Category Archives: Aggression

Conservation, Gombe, Health, Intergroup Conflict, Isotopes

Kalande

On June 10th, I traveled to the south of Gombe to visit the range of the little-known Kalande community of chimpanzees.

Map of Gombe National Park and chimpanzee ranges (from Rudicell et al., 2010)
Map of Gombe National Park and chimpanzee ranges (from Rudicell et al., 2010)

The Kalande community is one of three chimpanzee communities at Gombe.

The most famous, most intensively studied chimpanzees live in the Kasekela community in the center of the park. These are the chimpanzees that Jane Goodall has studied since 1960. They have the biggest range and the most members of the park’s three communities.

To the north of Kasekela live the Mitumba chimpanzees. This is a smaller community, which Deus Mjungu studied for his PhD research. The Mitumba community has fewer chimpanzees than Kasekela, but is still vigorous. They have a small range, but it includes excellent chimpanzee habitat with lots of food trees.

To the south is the Kalande community (also known as Bwavi). Most of the Kalande community’s range is grassland and woodland, with narrow strips of forest along the stream valleys. We know less about the Kalande chimpanzees than any of the others in Gombe. For the most part, these chimpanzees are still unhabituated, meaning they fear people. Researchers can follow the Kasekela and Mitumba chimpanzees around all day long, but they are lucky to get even fleeting glimpses of Kalande chimpanzees.

We aren’t even completely sure how many chimpanzees live in Kalande. Based on sightings and samples of genetically distinct individuals, there seem to be at least 9 chimpanzees in Kalande, but we don’t know for sure.

Skull from a male chimpanzee found dying in Kalande in 1994 or 1995.
Skull from a male chimpanzee found dying in Kalande in 1994 or 1995.

A small team of researchers monitor the Kalande chimpanzees. They collect fecal samples for genetic analysis, which enables us to keep track of individuals, even when we don’t know what they look like. Kalande has the highest rate of infection with the virus SIVcpz, which likely contributed to the decline of this community (Rudicell et al., 2010). Many females have left Kalande for other communities, both as part of the natural emigration process (females usually leave to join a new community when they are sexually mature), and because as Kalande declined, it eventually came to have too few males. Females seem to prefer living in communities with many males, both because many males are better able to defend the feeding territories that females need to survive and raise their offspring, and because females need unrelated males as mating partners. As the number of adult males in Kalande dropped down to one, or perhaps even zero, some Kalande females left for good, while others seem to have kept their Kalande home base, but visit Kasekela for mating.

Kat and Kazi, photographed when visiting Kasekela (20 April 2006)
Kat and Kazi, photographed when visiting Kasekela (20 April 2006)

Kati, for example, is a Kalande resident who has probably lived there since 1998.  Based on genetic data, we think she is the daughter of Patti who was known as Tita when she was younger. Since 2006, Kati has been making occasional visits to Kasekela. I saw her with her young son Kazi on one of these early visits. Of the Kalande chimps, Kati seems to fear people the least, which would make since if she grew up in Kasekela.

Deus and I took the boat to Kalande, where we met Ashaabu, one of the new Kalande research assistants. Ashaabu got his start working as a village Forest Monitor for his village’s forest reserve (part of the Greater Gombe Ecosystem project). Before going into the forest, we talked with Ashaabu for a while about which chimpanzees he has been seeing.

Kazi, who was just a little boy back in 2006, now seems to be the alpha male of Kalande, even though he is just a gawky adolescent. Based on how old Kazi looked back in 2006, I think he must be at least 12 years old now. Ashaabu says Kazi is around the size of the Kasekela male Fundi, who is about 14. The old male Renadi (or Leonard) hasn’t been seen for a number of years now, and I suppose must be dead. There might be another adolescent male, Pamera, but we don’t know for sure if he is still alive. Ashaabu has regularly seen Kati, Kazai, Katarina (Kati’s new baby), a big female without an infant, an adolescent female (who I think might be Pairott), and another young female around Kazi’s size. (Perhaps this is really Pamera? Might be hard to tell he’s a male if he’s still young and seen only briefly from a distance.) Ashaabu also mentioned Obedina, a female who had a big belly last year who might also have a new baby now.

After talking, we hiked into the forest, climbing a steep rocky path into Nyamagoma valley. Nyamagoma is the southernmost valley of the park, just north of Kazinga village. The path wound through an open woodland with a view of the lake below.

Ashaabu collecting Msongati fruits.
Ashaabu collecting Msongati fruits.

Along the way, we collected fruits and leaves for the isotope and nutrition projects. Given that Kalande has so much woodland, it will be interesting to see if the Kalande chimpanzees, or their foods, differ isotopically at all from those in Kasekela.

Ashaabu and Deus below a chimp nest.
Ashaabu and Deus below a chimp nest.

We followed the path down towards Nyamagoma Stream, where tall trees grew, shading the steep valley in green light. We didn’t see any chimpanzees, but we did see a number of nests. Chimpanzees build a new nest (or bed) in trees each night to sleep safely out of reach of any predators that might be lurking about. We found one cluster with five fresh nests, suggesting that up to seven chimpanzees might have slept there (if the group included Kati and Obedina and their new babies). It was encouraging to see so many fresh signs of chimpanzees using this valley. The Kalande community is still hanging in there, and perhaps they might recover, if the Kasekela males don’t catch Kazi and finish him off.

Ashaabu taking data on his tablet.
Ashaabu taking data on his tablet.

Ashaabu carried with him the tablet computer he had used as a Forest Monitor. He used the tablet to take pictures of the nests and enter the data, including GPS locations of the nests. It was quite stunning for me to think each of the villages around Gombe now has its own Forest Monitors, collecting data like this on their own village forest reserves, and loading it up regularly into the Cloud.

 

 

 

 

 

 

 

 

Director of Chimpanzee Research for Gombe Stream Research Centre.

 

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Intergroup Conflict

The Declining Effectiveness of Violence

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In The Better Angels of Our Nature, Steven Pinker argues that violence has declined over the course of human history. This weekend I had the good fortune to participate in a workshop that Pinker organized at Arizona State University on the Origins of Violence.

A number of the speakers were people whose work was central to the argument of Better Angels, which made the workshop feel a bit like stepping into the world of the book. Kind of like that scene in Annie Hall where a guy in line for the movies is holding forth on Marshall McLuhan’s ideas, and Woody Allen produces Marshall McLuhan in person to give his own views.

In addition to talks that elaborated on research described in Better Angels, there were also some pleasant surprises, particularly from a session of talks on why violence seems be declining, not only in frequency, but also in its effectiveness as a strategy.

In Better Angels, Pinker does a superb job of bringing together evolutionary theory, historical data, psychology and political philosophy to summarize and explain an important and under-appreciated finding: violence has decreased at multiple scales over the course of human history and prehistory. Despite claims on the news and by political leaders that the world is a more dangerous place than ever, the data indicate that the world has actually become substantially less dangerous, across the board.

Better Angels is also a big book (832 pages), and a surprisingly common theme of online commentary is “I haven’t finished reading the book, but here is my opinion of it anyway.” For example, here:  “I still haven’t finished all of its 800 pages,” and here: “I may as well admit that I haven’t read all of Steven Pinker’s new book.” But it’s a book worth reading all the way through.

Like Pinker’s book, the workshop covered a broad range of scholarship: behavioral ecology, ethnography, neuropsychology, political science, and history. A common theme was shared interests in answering big picture questions with empirical work, strong theoretical foundations, and a willingness to follow the results given by data even when contrary to conventional wisdom. Participants also included speakers invited for the Great Debate, a public event held Saturday evening, among them: evolutionary biologist Richard Dawkins, and one of my favorite science fiction writers, Kim Stanley Robinson.

For the workshop, 14 invited speakers each gave a 15-minute talk, followed by 5 minutes of discussion. Talks covered a wide range of material, but roughly speaking, focused on three main topics: (1) the causes of violence, (2) the decline of violence, and (3) the increasing ineffectiveness of violence. My own work focuses on the causes of violence, and Better Angels exhaustively outlines the evidence for the decline of violence, so I was least familiar with the third group of speakers, whose findings I found particularly novel and interesting.

Causes of Violence

The workshop began on Jane Goodall’s 80th birthday, so I thought it was very appropriate that we began with a discussion of chimpanzees killing each other. That was my talk. Richard Wrangham gave the next talk, in which he discussed violence in chimpanzees and warfare in human hunter-gatherers, drawing attention to some key similarities and differences. In both species, imbalances of power reduce the risks to attackers, making it cost-effective to kill rather than merely chase away enemies. In contrast to intergroup aggression in chimpanzees, human warfare appears to be more dangerous for the attackers, since humans are armed with weapons. This raises questions about what motivates people to undertake those risks. According to Wrangham, the answer is cultural rewards: warriors gain net benefits because their societies reward them for their deeds.

The remaining sessions all focused on humans, starting with a talk by Polly Wiessner, who is an extraordinary ethnographer. She has carried out decades of fieldwork both among the Ju/’hoansi Bushmen in Namibia and the Enga in Papua New Guinea. She compared and contrasted patterns of violence in the two societies. The Bushmen have a strong ethic of nonviolence but nonetheless have a high homicide rate, and few social mechanisms for dealing with the aftermath of violence. The Enga have lots of violence, including frequent warfare, but also have elaborate social mechanisms for negotiation and reconciliation.

Rob Boyd argued that group violence is common in other animals, but only because kinship underlies such violence (as in social insects, and competition between clonal colonies of sea anemones). Boyd argued that humans are unusual because we have lots of group violence among large groups of people who aren’t particularly close kin. In contrast to Wrangham, who focused on the rewards gained by human participants in warfare, Boyd focused on punishment as the mechanism that convinces warriors to risk their lives to benefit other group members. (For more on this, see contrasting papers: Matthew & Boyd (2011) and Glowacki & Wrangham (2013))

Adrian Raine talked about evidence from brain imaging studies about the mechanisms underlying criminal violence. Murderers tend to have low prefrontal cortex activity, indicating that they have trouble inhibiting their impulses towards violence. In contrast, psychopaths (such as serial killers) have strong prefrontal cortex activity, but unusually weak activity in key parts of the amygdala, suggesting that they kill because they have a problem feeling moral emotions. They might know that their actions are wrong; they just don’t feel that they are wrong.

David Courtwright spoke on themes developed in his excellent book Violent Land, which describes the impact of having unbalanced sex ratios in frontier societies. The take-home message: gathering lots of young, unmarried men in one place leads to lots of violence, especially if you add alcohol. Courtwright also talked about two other frontiers: air (early aviation was heavily male-dominated) and night (when city streets become more male-dominated and thus more dangerous).

So to summarize the causes of violence talks: the behavioral strategy of violence has deep roots in biology, but in humans we see an unusual level of group-level violence conducted by people who are not necessarily close kin. This seems to be supported by unusual patterns of grouping (reducing the costs of killing), combined with an unusual system of rewarding warriors and/or punishing cowards to promote participation in warfare. Among individuals, violence is promoted by dysfunction of particular brain regions, and among groups, violence is promoted when large numbers of unmarried men are gathered together. Societies may vary greatly in how they handle violence, but people everywhere face both the risk of violence, and the question of how to prevent violence.

Decline of Violence

The central argument of Pinker’s Better Angels of Our Nature is that warfare and other forms of violence have declined over time.  Pinker based his argument on extensive work by a number of other scholars, including several of the speakers invited to the workshop.

One of the key people who has assembled data on the high rates of violence in non-state societies is Azar Gat, author of War in Human Civilization. At the workshop, Gat talked about the ongoing debate between Hobbeseans and Rousseauites over the origins of warfare. Hobbeseans follow political philosopher Thomas Hobbes in arguing that the ancestral condition of humanity was war of all against all. Rousseauites follow Jean-Jacques Rousseau in arguing that the state of nature was a peaceful world of noble savages. Gat argued that while this debate might seem unresolvable, in recent years Rousseauites have shifted their positions, effectively conceding that the evidence indicates humans have a long history and prehistory of some forms of violence, including homicide and feuding, even if Rousseauites continue to disagree about the evidence for early war.  Gat also argued that, in contrast to the Rousseauite anxiety that arguing for evidence of a warlike past promotes a warlike future, the existence of prehistoric warfare is no impediment to building a more peaceful future.

Another key person documenting the decline of violence is Manuel Eisner, who has conducted meticulous studies of European historical records, leading to the discovery of a striking decline in homicide rates in Europe over the past 600 years. He presented new data both on overall homicide rates, and on regicide (take home message: it’s dangerous to be king!).

The workshop also included two people who have documented the recent decline in warfare: John Mueller and Joshua Goldstein. Based on studies of the number of ongoing wars per year, Mueller has concluded that “war has almost ceased to exist.” Great powers no longer engage in direct warfare with each other, and even minor powers seem increasingly reluctant to fight wars.  Goldstein has argued that, despite the US being involved in wars in Iraq and Afghanistan, “the decade since 9/11 has been the most peaceful worldwide in the past century.”

Christopher Fettweis presented detailed work on mortality from warfare over the years in Africa. Back in 1994, Robert Kaplan predicted “The Coming Anarchy,” in which West Africa in particular would be overwhelmed by rapidly growing populations, chaos and warfare. In contrast, what the actual data show is that over the ensuing decades Africa has become increasingly peaceful. Fettweis argued that Africa likely now enjoys a lower risk of death from warfare than ever before. Today, the average person living in Africa is less likely to die from war than the average American is to die from homicide.

So despite claims from political leaders that the world is “more dangerous than it has ever been,”  the risk of dying from violence, including homicide and war, actually has decreased considerably across history and (as far as we can tell) prehistory.

Ineffectiveness of Violence

There are many possible reasons for the decline of violence. One important reason may be the growing recognition that violence is a decreasingly effective way to accomplish goals.

 Max Abrahms argued that based on empirical data, terrorism usually fails to accomplish the goals of terrorists. In particular, killing civilians – the most feared practice of terrorists – is usually self-defeating: groups that kill civilians are more likely to fail in attaining their goals. So why do terrorists ever do this? Abrahms argued that it is mainly the lower-ranking members of organizations with weak leadership that carry out such attacks. Attacking “hard” targets like military bases is, well, hard. It’s easier to attack “soft” targets like cafes and buses, so that’s what low-level terrorists do, especially when their more experienced bosses don’t have sufficient control to stop them. In contrast, the more experienced, higher-level terrorists gradually learn that killing civilians is counter-productive and focus instead on different goals. Based on this finding, the current US strategy of using drones to “decapitate” Al Qaeda by killing leaders is likely increasing, rather than reducing, the likelihood of attacks on civilians by this organization.

Continuing on the topic of terrorists, Adam Lankford took a critical view of suicide terrorism, in the context of self-sacrificial behavior in general. Lankford argued that intentionally self-sacrificial behavior is rare: mother mammals rarely give up their lives to save their young (their fitness benefits more if they live to breed another day), and soldiers don’t fall on grenades. Soldiers do sometimes move towards grenades to throw them back at the enemy, or attempt to smother them with a backpack, helmet or boot, but they don’t lie down on a grenade and wait for it to explode into their bodies. Lankford further argued that many suicide terrorists are really just suicidal. Moreover, Lankford argued that suicide terrorism isn’t terribly effective, that it fails in about half the cases, and even when successful rarely kills many people. Lankford’s results, combined with Abrahms’s arguments that terrorism against civilians is counter-productive, suggest that terrorism is just a really bad strategy.

Instead, based on Erika Chenoweth’s findings, people seeking political change would be better off doing so nonviolently. With a meticulous, skeptically motivated empirical study, Chenoweth found that nonviolent campaigns are about twice as effective as violent rebellions in accomplishing their aims, such as removing leaders and winning territorial independence. Since the end of World War II, nonviolent campaigns have also become more common as a strategy. And unlike violent rebellion, they don’t benefit much from foreign intervention – they need to be home-grown to work effectively. The key seems to be getting a sufficiently large proportion of the society involved: groups with at least 3.5% of the population participating always achieved their aims. Additionally, the methods used to gain power have important impacts on how groups govern if they are successful. Nonviolent groups are more democratic and respect human rights more so than groups that gained power through violent means.

None of this means that we live in a world without danger of warfare and other kinds of violence. The recent events in Ukraine make that clear. Nonetheless, those very events help illustrate some key points. First, the nonviolent protests against Ukraine’s government succeeded in removing an unpopular leader. Second, the subsequent invasion of Crimea by Russia resulted in only two casualties and an election. While the invasion clearly carried the menace of violence, and the election was certainly far from fair, both were a far cry from what would have happened in previous decades.

Given the rhetoric of pundits and political leaders that we live in a dangerous world, it is important to realize that, compared to almost all of recorded history, the world today is remarkably peaceful. Moreover, in today’s world, peaceful methods are frequently more effective than violent ones.

Interested in learning more about what these speakers have to say? Check out the Origins of Violence Reading List!

References

Glowacki, L. and R. W. Wrangham (2013). “The Role of Rewards in Motivating Participation in Simple Warfare.” Human Nature-an Interdisciplinary Biosocial Perspective 24(4): 444-460.

Mathew, S. and R. Boyd (2011). “Punishment sustains large-scale cooperation in prestate warfare.” Proceedings of the National Academy of Sciences of the United States of America 108(28): 11375-11380.

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

Gombe, Intergroup Conflict

Hunting and Fighting

In chimpanzees, intergroup aggression and hunting look quite similar in several ways. Both hunts and intergroup attacks are mainly the business of males. In both cases, groups of males climb, leap, and run after a victim, which, if they catch, they will bite and pummel until it stops moving. Attacking males bristle their hair like fighting cats, making them look even bigger than they really are. They bare their teeth in fearful grimaces and scream.

Red colobus leaping to escape chimpanzees.

Since the 1970s, researchers have speculated that hunting and fighting in chimpanzees are related, resulting, perhaps, from the same psychological mechanisms. For example, chimpanzees’ close relatives, bonobos, have not been observed to kill other bonobos, and bonobos rarely hunt. Perhaps the two behaviors are linked? For example, my thesis advisor Richard Wrangham has speculated that as bonobos evolved from a chimpanzee-like ancestor, “males lost their demonism, becoming less aggressive to each other. In so doing, perhaps they lost their lust for hunting monkeys, too.” (Wrangham & Peterson 1996: 219)

Ten years ago, when I was a post-doc with Anne Pusey, in the early stages of extracting records on intergroup aggression from the long-term data at Gombe, I looked at seasonal patterns of intergroup encounters, as part of an effort to understand why such encounters occurred. From the limited sample of years for which I’d extracted data, intergroup encounters occurred most often in the late dry season (September and October) with a smaller spike in the middle of the wet season (February). When I compared notes with Anne’s graduate student, Ian Gilby, I was struck that he had found essentially the same pattern with hunts: the number of hunt attempts per follow peaked in the late dry season and mid wet season. Additionally, comparing five years for which we both had data, we found that years with more hunting success also had more patrols. Was this because hunting and intergroup fighting were caused by the same factors?

We agreed we should work on this further, and now that work has born fruit: a forthcoming paper in Animal Behaviour by Gilby, Wilson and Pusey.

Frodo being groomed by Apollo.

A key inspiration for this work was one male chimpanzee, Frodo. Frodo was the best hunter at Gombe when Ian was doing his dissertation research. Frodo was involved in all four intergroup killings that I described in my first Gombe paper (Wilson et al., 2004). I had watched video, frame by frame, of Frodo brutally attacking a young male chimpanzee from the Kalande community. Maybe Frodo was a great hunter because he was a great fighter? Frodo was also exceptionally persistent in pursuit of estrous females, and genetic studies found that Frodo had fathered more babies than any other Gombe male. I began to wonder if in chimpanzees, hunting and fighting were both byproducts of selection for skills needed to achieve mating success.

Male red colobus monkey jumping down to chase Titan, Fundi and Frodo.

Ian kept Frodo very much in mind when he went on to work as a post-doc with Richard Wrangham on data from Kanyawara. Ian proposed that a key part of group hunting in chimpanzees was the presence of particular individuals who really liked to hunt – which Ian termed “impact males.” As a group-level activity, hunting suffers from potential collective action problems. Hunting is risky and dangerous. Red colobus monkeys don’t want themselves or their babies to get eaten, and they fight back fiercely, biting with their sharp teeth. Individuals therefore might be tempted to free-ride – let others do the hunting, and then get meat afterwards, by begging, stealing, or scavenging what’s left when others are done eating. But if everyone free-rides, no one will hunt. So how does hunting get started? Ian proposed that some individuals, the impact males, are strongly motivated to hunt – and once they get started, others are encouraged to join in, because the costs of joining a hunt already in progress are less than the costs of starting the hunt.

Titan, Fundi and Frodo looking at red colobus monkeys, deciding whether to hunt.
Titan, Fundi and Frodo looking at red colobus monkeys, deciding whether to hunt.

The logic of “impact males” made sense to me, not only for hunts, but also for territorial behavior. Patrolling boundaries is energetically expensive and potentially dangerous, as patrols can meet a big group of hostile neighbors. Patrols therefore seem vulnerable to the same collective action problems as hunts. So maybe they are solved the way: some individual males are strongly motivated to go on patrols, reducing the costs for everyone else to join in. After all, if I know at least one of my buddies is going on patrol, I know I won’t be alone at the edge if I go with him. And perhaps – maybe these are all correlated for the same reason? Maybe the same males are impact hunters and impact patrollers? And maybe these same males are the ones who are really good at winning dominance interactions, gaining high rank, and getting access to fertile females and fathering lots of babies? Maybe these are all correlated traits, parts of an overall personality profile or behavioral syndrome of what it takes to be a successful male chimpanzee?

We now had lots more data to work with than we did a decade ago: 32 years of data on both hunting and boundary patrols. And we found that hunting and patrolling boundaries were indeed correlated, not just on a monthly basis, but also on a daily basis. However, it turned out that hunting and patrolling were mainly correlated because of the influence of other variables. Both hunting and patrolling were more common when males were in large parties – which we expected, because parties with more males are more likely to succeed, both in hunts and in intergroup encounters. But the main reason hunting and patrolling were correlated was because both involved long-distance travel. When chimpanzees patrol their borders, they necessarily travel a long ways. And when they travel a long ways, they are more likely to encounter monkeys.

We found that there were indeed impact males for both hunting and patrolling. But only one of the males who was an impact hunter was also an impact patroller. And surprisingly, good old Frodo was neither an impact hunter nor patroller. He had a positive impact on hunting probability, but not enough to merit status as an impact hunter. And the probability of patrolling was the same, with and without Frodo in the party.

So these results suggest that hunting and fighting, despite their many resemblances, may result from different psychological mechanisms. In some ways this is not really surprising, given that in species whose brains have been studied in detail, such as rats and cats, aggression and predation involve quite different regions of the brain. Additionally, Marissa Sobolewski has looked in detail at the hormones of male chimpanzees from the Ngogo community, going on two different kinds of patrols: hunting patrols, in which males are looking for monkeys, and border patrols, in which males are presumably looking for neighbors. Marissa found that testosterone levels were elevated for border patrols, but NOT for hunting patrols. This strongly suggests that hunting and fighting do indeed result from different psychological mechanisms in chimpanzees.

Our findings from the long-term data are thus rather different from what we thought we’d find. This illustrates the importance of looking at data, not just theory, when doing science. It’s easy to fall in love with hypotheses, but they need to stand the test of empirical work. Nonetheless, I still suspect there may be interesting links in the psychology of hunting and fighting. For example, tendencies towards pugnaciousness and risk-seeking seem likely to benefit both hunting and fighting (and acquiring mates). But from the data we’ve examined so far, being a top hunter doesn’t automatically make one an influential boundary patroller.

(For more on Frodo, see Ian’s biography of Frodo, Lisa O’Bryan’s description of Frodo in retirement and this picture of baby Frodo.)

Intergroup Conflict, Kanyawara, Numerical assessment

Fighting over Food

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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, Xenophobia

Evolution is not just for Democrats

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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.

Intergroup Conflict, Numerical assessment

Hyenas can count

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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.

Intergroup Conflict, Religion

Will the New Atheism Save us from Jihad?

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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

Xenophobia and Immigration

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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.