Category Archives: Evolution

Causes of Death in Chimpanzees

As George Carlin says, “It’s inevitable when you buy the pet. You’re supposed to know it in the pet shop. It’s going to end badly. You’re purchasing a small tragedy.”

The same goes for studying animal behavior. Anyone who spends enough time in the field, getting to know the lives of animals, will also witness their deaths. In a new paper, “Pathologic lesions in chimpanzees (Pan troglodytes schweinfurthii) from Gombe National Park, Tanzania, 2004-2010,” we report on some of the things we’ve learned from chimpanzees who have died. This paper, led by Karen Terio at the University of Illinois, involved a large team of field researchers, veterinarians, and pathologists.

I started studying chimpanzees because I was interested in how they lived. But in studying their lives, I’ve seen many of their lives come to an end. In this way, studying chimpanzees is a bit like being an Elf in J. R. R. Tolkien’s Middle Earth. In Tolkien’s world, the Elves live for centuries, dying only if they encounter some mishap, such as being slain in battle. In a single life, an Elf such as Elrond watches sadly as generations of mortal men come and go. In a similar manner the generations of chimpanzees, though long by the standards of typical mammals, pass more quickly than those of our own species. Jane Goodall, who has been watching chimpanzees at Gombe since 1960, has seen entire generations come and go. Chimpanzees that Jane saw as newborn babies have grown old and died, and their children, grandchildren, and now great-grandchildren have been born. I’ve only been working at Gombe since 2001, but this is still long enough that many of the chimpanzees I’ve gotten to know there have since passed on: Fifi, Goblin, Vincent, Ebony, Andromeda, Patti, Ebony, Sherehe, Shangaa, Echo, Yolanda, Malaika, Kris, and others.

I knew each of the 11 chimpanzees we describe in this new paper, except for a stillborn baby. I was involved in various ways with documenting the ends of their lives, such as taking observations during their final days, helping with the recovery of their bodies after death, examining the bodies immediately after death, organizing and participating in the necropsies, burying the bodies and recovering their skeletons from their graves, after they had been buried for at least a year. My student Claire Kirchhoff examined these skeletons for evidence of trauma.

Determining the cause of death is important for many reasons, including understanding chimpanzee life histories and identifying threats to their conservation. Because my research focuses on aggression, it’s especially important for me to know the cause of death. Did they die from aggression, or some other cause? In each case, it’s important to document carefully the relevant evidence.

Graucho Marx said, “Outside of a dog, a book is man’s best friend. Inside of a dog, it’s too dark to read.”

I’ve never tried reading inside a dog, but I’ve ended up sending more time looking at the insides of chimpanzees than I ever expected. If I had known what the future held for me, I would have taken some proper anatomy courses. But fortunately at Gombe, we’ve benefited from a wide range of expertise, including the Health Monitoring Project led by Elizabeth Lonsdorf and Dominic Travis, and the virology study led by Beatrice Hahn. We’ve been able to store chimpanzee bodies in large freezers until we can assemble teams of experts to conduct necropsies. We send tissue samples to pathologists and molecular virologists to gain a finer grained understanding of the causes of death.

I study violence in chimpanzees, not because I like violence (I don’t), but because it plays such an important role in the lives of chimpanzees – and as one of the two species most closely related to humans, chimpanzee violence can help us understand violence in our own species. Chimpanzee violence caused 36% of deaths in this study – more than any other factor. Andromeda and Patti were killed during intergroup attacks. Vincent was killed by members of his own community. Ebony – found dead with a broken neck and puncture wounds – almost certainly killed by chimpanzees, and likely one or more of the males of his own community.

One of the humbling things about research is that often, even with all the expertise we can muster, there is much that we will never know for sure. One such case involves the adult female Echo, who became a long-term resident at Kasekela at about the same time that I did.  I caught my first glimpse of Echo during one of my first days in the field as Director of Field Research at Gombe, back in January 2004. While we were watching a large group of chimpanzees feeding in the trees above a steep valley, videographer Bill Wallauer pointed out a new immigrant female chimpanzee with a pretty face and an asymmetric, bumpy sexual swelling. Bill recognized her from pictures he had taken in 1999, and thought she might be a female seen during an intergroup encounter in 2003. We named her Echo because she seemed to keep bouncing back. Unusually, Echo had immigrated together with her juvenile daughter, who we named Eowyn, after the heroic shieldmaiden from Tolkien’s Lord of the Rings.

Eowyn inflicting fatal trauma on the Witch-King of Angmar

Usually, females only move from one community to another as adolescents, before they have children. Infants of immigrants face a high risk of being killed by the resident males, as nursing infants fathered by other males represent both genetic competition and an unwelcome form of contraception. But Echo chose a good time to immigrate: her daughter Eowyn was weaned, and Echo had a full sexual swelling. The Kasekela males left Eowyn alone, and Echo quickly conceived a daughter, Emela.

Genetic analysis of fecal samples confirmed that Echo used to live in the Kalande community. Her departure from Kalande showed just how bad the decline of that community had gotten. Usually, once females have settled into a community and have started having babies, they stay there for life. But females seem to prefer living in a community with multiple males, which may be important both to protect them from intergroup aggression and to provide them with some good options for mates. Echo left when the number of adult males in Kalande dropped to one.

We also learned that Echo was infected with SIVcpz, the virus that is the immediate precursor of HIV-1, which causes AIDS in humans. Four of the 11 chimpanzees in the new study were infected with this virus. Until recently, it was widely assumed that SIVcpz was harmless in chimpanzees. We learned from studying Gombe chimpanzees, though, that infection with this disease greatly increases mortality risk. Two of the chimpanzees in this study died from AIDS-like symptoms.

Echo and Emela

I particularly remember Echo from a day in March 2006. In the late afternoon, the chimpanzees climbed high into a hill above Kasekela valley, into an open woodland. They climbed into the short, stunted trees to feed, rest and groom. Echo climbed rested on a low limb and groomed with Tubi, Bahati and her son Baroza. All seemed peaceful and happy. Echo had immigrated successfully, settled into Kasekela, had a daughter, and made friends.

But this was not to last.

Paralyzed "Patina"

In November 2006, which happened to be my last month of being based full time at Gombe, field assistants monitoring the Kalande community reported that one of their females, Patina, was sick. Together with vet Iddi Lipende, I traveled down to Kalande to investigate. We found a female chimpanzee lying in a dry streambed, her legs apparently paralyzed. She looked at us fearfully. She was too weak even to shoo away the flies that gathered at the wounds she had inflicted on herself, dragging her broken body along the stones of the dry streambed. She died within a few days.

In the following months, analysis of genetic samples found something puzzling: new fecal samples continued to come in from a female who was an exact genetic match for Patina. Apparently it wasn’t Patina who lay dying in that streambed – it was someone else. Given that the Kalande chimpanzees aren’t habituated, a case of mistaken identity was not so surprising. But the puzzle remained: who was the female who died?

Around this time, Echo’s daughter Eowyn showed up in Kasekela without her mother – something unusual for such a young chimpanzee. And genetic analysis of the tissue from the dead female found that she was, in fact, Echo. She had gone back to her home community of Kalande and died there. In her weakened state, she looked so different that none of us had recognized her. Her infant Emela had disappeared and must have died as well.

The necropsy found that Echo had a broken spine, but we don’t know how she broke it. She didn’t have the other injuries typical of a chimp attack – no canine puncture wounds, missing fingers or toes – so it seems unlikely that chimpanzees had killed her. Did she fall from a tree? If so, why? Was she chased by other chimps? Or did she just have bad luck? We will never know.


Here are the publications where we report some of the findings discussed here:

Keele, B. F., J. H. Jones, K. A. Terio, J. D. Estes, R. S. Rudicell, M. L. Wilson, Y. Li, G. H. Learn, T. M. Beasley, J. Schumacher-Stankey, E. E. Wroblewski, A. Mosser, J. Raphael, S. Kamenya, E. V. Lonsdorf, D. A. Travis, T. Mlengeya, M. J. Kinsel, J. G. Else, G. Silvestri, J. Goodall, P. M. Sharp, G. M. Shaw, A. Pusey, E. and B. H. Hahn (2009). “Increased mortality and AIDS-like immunopathology in wild chimpanzees infected with SIVcpz.” Nature 460: 515-519.

Rudicell, R. S., J. H. Jones, E. E. Wroblewski, L. G. H., Y. Li, J. Robertson, E. Greengrass, F. Grossmann, S. Kamenya, L. Pintea, D. C. Mjungu, E. V. Lonsdorf, A. Mosser, C. Lehman, D. A. Collins, B. F. Keele, J. Goodall, B. H. Hahn, A. E. Pusey and M. L. Wilson (2010). “Impact of Simian Immunodeficiency Virus Infection on chimpanzee population dynamics.” PLoS Pathogens 6(9): e1001116.

Terio, K. A., M. J. Kinsel, J. Raphael, T. Mlengeya, I. Lipende, C. Kirchhoff, B. Gilagiza, M. L. Wilson, S. Kamenya, J. D. Estes, B. F. Keele, R. S. Rudicell, W. Liu, S. Patton, D. A. Collins, B. H. Hahn, D. A. Travis and E. V. Lonsdorf (2011). “Pathological lesions in chimpanzees (Pan troglodytes schweinfurthii) from Gombe National Park, Tanzania, 2004-2010.” Journal of Zoo and Wildlife Medicine 42(4): 597-607.

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.


After starting this blog in August, I hardly blogged at all during the semester. Partly this was because with my teaching and other duties, I had little time to spare for blogging. And in what spare time I did have, I wasn’t thinking about blog topics. I was thinking about my Mom, who was fighting what turned out to be a losing battle with leukemia.

Years ago, as the stem cells in Mom’s bone marrow were going about their usual business of dividing to make cells that would in turn give rise to new blood cells, one of them made a mistake. A deletion occurred on Chromosome 9. That cell divided and gave rise to a whole lineage of cells with the same deletion. Over time, some other cells in that lineage arose with additional genetic errors that prevented them from making proper blood cells. Instead, they produced millions and millions of daughter cells that filled up Mom’s marrow with useless cells, crowding out the good cells.

Mom only became aware that there was a problem a couple of years ago, when she was diagnosed with Myelodysplastic Syndrome (MDS), which often develops into leukemia. And in Mom’s case it did. In March, on her birthday, she was diagnosed with Acute Myeloid Leukemia (AML) and soon started her first round of chemotherapy.

Mom faced all of this with remarkable courage. In the hospital, she joked, made light conversation, took photos of all her visitors, and kept her good humor through all of the indignities of hospital life – the flimsy gowns, the lack of privacy, the constant parade of people coming into the room to do this or that, the increasing need for other people to help with basic bodily functions. Mom accepted all of this gracefully. Though she did not like revealing her birth year to other people, in the hospital many times a day she cheerfully gave her name and birthdate to hospital staff, as required when receiving new medications or blood transfusions. She always liked to look her best. When the chemo caused her hair to fall out, she wore wigs and hats – but mainly to make her visitors comfortable. Over Skype, she asked us if we wanted to see the bald head, and showed us when we said yes, seeming entirely cheerful and matter-of-fact about the loss of the hair that she had been so careful to keep just so over the years.

As a family, we tried to learn as much as we could about Mom’s condition and treatments. Dad bought and diligently read a medical textbook on hematology. This information was interesting enough, and helped us understand what Mom was going through, but we never found what we were looking for: some hidden nugget that would help Mom live. And the scientific literature was far from comforting. Studies of AML (such as here and here) found that for most patients, even with the best treatments available, life expectancy was a matter of months rather than years, especially if they were older, had a background of MDS, and had multiple detectable genetic changes in their chromosomes.

I’m not sure what I imagined chemotherapy would be like, but the actuality was both more peaceful and more awful than I had expected. For the most part, it involved just waiting in the hospital room, attached to a rack full of IV bags dripping an array of different fluids, including saline solution, blood, plasma, and chemotherapy drugs, into a PICC line – a tube inserted into the arm that directed the incoming fluids right to the heart. At first, it hardly seemed like Mom was really sick. She was just like she always was, except confined to a hospital room and attached to an IV drip. But gradually the chemo did its job and took its toll, and Mom got sicker and sicker.

One of the chemotherapy agents that Mom received was Cytarabine. This is chemically nearly identical to cytosine, one of the four bases that make up DNA. It is similar enough that it gets incorporated into new DNA, but different enough that that new DNA doesn’t work properly, and the new cells die as a result. So all the rapidly dividing tissues – cancer cells, but also hair, skin, and the intestinal lining – suffer as a result, resulting in all the usual chemotherapy side effects.

Another chemo drug Mom had was Daunorubicin – a ruby colored compound isolated in the 1950s from soil-living fungus in Italy and named for a pre-Roman tribe, the Dauni. The bright ruby color of this drug made it look especially potent and menacing when it was injected. Daunorubicin molecules are just the right shape to slip in between successive base pairs in DNA strands, unwinding the DNA a bit and interfering with replication. Again, this wreaks havoc, not just on cancer cells, but also on all healthy tissues that rely on rapid cell division.

Mom endured two rounds of chemo, achieved remission, and came home, where before long, life almost seemed back to normal. She cooked dinners, played bridge, went to church, and even traveled across the country to see her newest grandchild. It started to seem that Mom was healthy and out of danger.

However, while the chemo had killed a lot of cells, it hadn’t completely wiped out the mutant stem cells. Instead, the few surviving mutant cells continued to replicate, acquiring new mutations on the way. By September, the leukemia was back, and just before Thanksgiving, it took Mom away from us.

The chemo took a terrible toll, but without it, what happened in November would have happened in March. Thanks to the chemo, Mom had a summer at home, visits from her children and grandkids, and time to say goodbye.

Mom wanted to live, but during what turned out to be her final hospital stay, she talked of how the quality of life, and the prospects for improving it, diminish. In one of our last conversations, she told me, “I had hoped to live long enough to see how things turned out for everyone. But then, even if we lived to be over 100, we would still want more.”

Mom was one of the very best people I have ever known, and it seems terribly unfair that she should be taken from us so soon. It’s hard to believe that such a vibrant person, so full of love and caring and thoughtfulness, the keeper of so many family memories and traditions, should be undone by the information copying errors of the tiny, mindless cellular machinery of her own body.

Around the time Mom got sick, my computer crashed. The Genius at the Apple Store said it was a problem with the logic board, and that there was really nothing to be done, since the repairs would cost about as much as a new computer, and that in a computer of such advanced age (nearly five years old!), more problems would soon be arising. Luckily I had my data backed up, and almost all the files on my old computer are now on my new computer. But Mom is gone. There’s no backing her up.

Religious minded people will be tempted to provide reassurance that Mom is in Heaven. That’s certainly what Mom believed, and if such a place exists, then surely she is there. But my own inclination is to think that we are material beings, and that our lives begin and end on earth. This materialist view provides its own comforts. “No Hell below us – above us, only sky.” There is no one to blame for the loss of loved ones: it just happens. But whatever one believes about the metaphysical, Mom left behind a great big hole here on earth.


With the start of the semester, I’ve been too busy teaching to write new posts for the blog, so lately, the site has served only to attract spam.

Some of these spam comments are quite cunning. They usually involve some sort of flattery. Here’s one example:

“Saved as being a favored, I truly like your weblog!”

I was fooled into thinking this was a real comment at first. Then I got an onslaught of similar comments, such as:

“Nice post. I learn something more challenging on different blogs everyday. It will always be stimulating to read content from other writers and practice a little something from their store. I’d prefer to use some with the content on my blog whether you don’t mind. Natually I’ll give you a link on your web blog. Thanks for sharing.”

“I just now adore to learn different themes within you blog page.”

“This article ahceived exactly what I wanted it to achieve.”

“Son of a gun, this is so hlepufl!”

That’s the hook. Softened by flattery, the blogger allows the comment to be posted. Now comes the benefit to the spammer: the comment includes the spammer’s URL – which is always some commercial site that they want you to visit. So it’s a cheap way to manipulate blogs into providing free advertising.

It’s annoying to get message after message that just turns out to be cleverly disguised spam (“Lobster Thermidor aux crevettes with a Mornay sauce served in a Provençale manner with shallots and aubergines garnished with truffle paté, brandy and with a fried egg on top and spam!”).

But it’s also quite a nice example of manipulation in the evolution of a communication.  As Dawkins and Krebs have argued, from an evolutionary perspective, we would expect communication mainly to involve attempts to manipulate others. The signaler tries to get the listener to do something for the signaler. My baby fusses, for example, because she wants me to carry her, or she wants her diaper changed, or wants to be fed. She wants something, and she can get it from me by making signals that I simply can’t ignore. Of course, with my baby, I don’t mind the manipulation, because she’s my baby. But the spambots with bad spelling and mangled grammar – those I could do without.

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.

Does it matter whether people believe in evolution?

Yesterday, I was talking with a friend about politics and evolution. He asked, “Creationism is pretty harmless, though, right? It doesn’t really hurt anyone.”

I suppose for most people, the question “Do you believe in evolution?” seems to matter about as much as the question, “Do you believe in Bigfoot?” Bigfoot might be there, or he might not be, but whether he is or isn’t doesn’t make much difference in their lives. But even though most people may not think about this issue much, I think Creationism does hurt people, and in two main ways. First, evolutionary theory has many practical applications for all sorts of different topics: geology, medicine, agriculture, economics, advertising, mate choice, and pretty much anything else that has anything to do with biology. A proper understanding of evolution can help people make better decisions regarding all sorts of practical matters. Creationism hurts people by closing their minds to this useful information. Second, evolutionary theory opens the doors to a profound and beautiful view of the world. Creationism hurts people by robbing them of a deeper understanding of what the world is, and how it came to be.

By Creationism, I mean the belief that God created the world suddenly, pretty much as it is now, some time in the recent past. This is different from, say, theistic evolution, advocated by people like the great dinosaur scientist Robert Bakker (who apparently is also a Pentecostal preacher). Advocates of theistic evolution accept scientific evidence that the world is very old and has come into its present form through billions of years of gradual changes. (I’m not a religious person myself, but can see how theistic evolution would be an attractive and reasonable view for many people who are religious.)

As an example of where the practical and poetic sides of evolution meet, think of the southern shore of Lake Michigan, where the Indiana Toll Road passes through the huge industrial wastelands of Gary:US Steel plant in Garythe grim, depopulating city to the south, the smokestacks, blast furnaces, and slag heaps to the north, mile after mile of rustbelt ruins littering the shores of an inland sea. The steel industry made Gary a boomtown, and the industry’s decline has left it a husk. But some of the factories are still working, and they depend for their work on key three main ingredients: iron, coal, and limestone. Factories make steel by smelting iron in blast furnaces with coke (a purified form of coal) and limestone. The burning coke melts the iron and provides carbon, which combines with the iron to make steel. Limestone removes impurities from the iron, resulting in slag. Gary provides a convenient place for steel factories because it lies close to sources of coal (Illinois) and limestone (Indiana), and is connected by the Great Lakes to a major source of iron (Minnesota).

We owe coal, limestone and iron to three key evolutionary events: the invention of trees, shells, and plants.

Coal Forest Swamp. Used with permission of the artist, Richard Bizley (

The most recent of these is the invention of trees, which resulted in the formation of coal. The coal in Illinois formed during the Pennsylvanian period, just over 300 million years ago, when what is now Illinois was covered by vast, low-lying tropical rainforests. We know from fossils preserved in coalmines that these forests looked unlike any living forests. They had giant club mosses and tree ferns and all sorts of huge versions of plants that survive today only as small forms living in the shadows of more modern trees. These plants were able to grow so tall thanks to a newly evolved fiber, lignin, which they used to make strong, woody stems. In addition to helping the trees grow tall, lignin toughened their bark and protected them from insects, which could not digest the tough fiber. Neither could any of the bacteria or fungi that existed then. As a result, when these trees died, instead of rotting, they piled up and gradually turned into coal. As a result of all this accumulating carbon, the atmosphere developed a growing surplus of oxygen – which may explain the evolution of giant insects and other arthropods, including dragonflies with wingspans two feet wide and millipedes six feet long. Our very distant ancestors, early amphibians, crept and swam about in these swampy forests.

Living foram

The invention of shells occurred much earlier, shortly before the Cambrian period, which started around 543 million years ago. We don’t know much about life before the invention of shells, because animals without hard parts don’t fossilize very well. But once shells were invented, we get lots and lots of fossils – including huge beds of limestone, made almost entirely from the shells of tiny animals, especially foraminifera: single-celled amoebas that live in tiny shells called tests. Indiana limestone was laid down in the Mississippian period, around 335 million years ago. At the time, a vast shallow sea covered much of Indiana. As tiny marine organisms died, they rained down to the bottom of the sea, their shells contributing bit by bit to what would eventually become limestone.

The invention of plants – or more precisely, photosynthesis – occurred even earlier, and had a profound effect on life on earth. The first creatures to capture sunlight to make food were bacteria. Eventually some of these, such as blue-green algae, developed a method of photosynthesis that produced oxygen as a waste product. At the time, oxygen was poisonous to most living things. As the oxygen waste built up in the atmosphere, some species evolved ways to deal with the poison, but most went extinct, or survived as refugees in crannies hidden from the deadly air. As oxygen dissolved in the sea, it combined with iron compounds already dissolved in the water to make iron oxide (rust), which sank to the bottom and accumulated in layers on the sea floor. The resulting banded iron formations of the Minnesota Iron Ranges are thus the result of biological activity some 2,000 million years ago.

Abandoned iron mine outside Virginia, Minnesota

Evolution is not just some story. It’s the explanation for how we get iron, limestone and coal. Without an understanding of evolution, we wouldn’t know where to look for these minerals – or other fossil formations, like oil. Knowing about evolution helps us understand that our supply of these fossil resources, however large, is ultimately limited. And without the glacial lakes formed at the end of the last Ice Age some 10,000 years ago, we would have a much harder time getting the iron from Duluth to Gary.

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.

Rehabilitating “Monkey”

Think of a monkey.

What do you see?

I bet that most people picture a chimpanzee, most likely a juvenile chimpanzee, like Curious George (who in the books is always called a monkey). Even though adult chimpanzees look rather like small gorillas – they walk on all fours, they are nearly as big as people, and they are tremendously strong – most people seem to think of chimps as “cute little monkeys.” The monkeys in a Barrel of Monkeys are chimps. Do a Google Images search for “monkey” and you will get some pictures of proper monkeys, but you will also get lots of chimps.

Anyone who knows something about primates, though, knows that chimpanzees are not monkeys. They are apes. And what are apes? They are a group of primates from the Old World (Africa and Eurasia) that don’t have tails. There used to be many more species of them, millions of years ago, but now we just have twenty-odd species, most of which are different kinds of gibbons, plus siamangs, orangutans, gorillas, chimpanzees, bonobos, and humans.

For many years, people used the word “ape” to mean the group of Old World primates that didn’t have tails, but that weren’t humans: that is, all of the apes except us.

More recently, biologists have argued that when we classify living things, we should use only monophyletic groups: groups in which all members are descendents of a common ancestor. Since humans evolved from apes, then, strictly speaking, we are apes.

So what about monkeys? If the term “monkey” does not include the apes, then it is no longer a monophyletic group. A good monophyletic group should include all of the descendents of a common ancestor. In the jargon of taxonomy, Old World monkeys and apes are classified together as Catarrhines (“downward noses”), while monkeys from the New World (North and South America) are classified as Platyrhines (“flat noses”). These are good monophyletic groups. But nobody uses jargon like this in ordinary language. If we translate these terms into ordinary language, we get Old World monkeys (which, to be monophyletic, must include the apes) and New World monkeys. So apes are all monkeys. Which makes you and me monkeys. And any man whose siblings have reproduced is a monkey’s uncle.

So I suggest that we rehabilitate the word “monkey” as a perfectly good word to use in describing chimpanzees and all the other apes, including us. Apes are just one particular branch of the monkey family tree.

When I discussed this in class this spring, one of my students complained that officially classifying apes as monkeys would rob him of the pleasure of correcting strangers at the zoo when they go around calling gorillas and orangutans “monkeys.” To me, though, this seems like a happy case in which ordinary language fits perfectly well with good biology.

This doesn’t always have to be the case. I expect it will take people a while longer to get used to the idea that birds are dinosaurs, and that, monophyletically speaking, we are all fish.