All posts by DaktaMaik

Cousins Gossamer and Glamour at termite mound.
(11 June 2014)

Twins and Cousins

Gombe is a special site for many reasons. Among them: It is the first site where wild chimpanzees were observed to make and use tools. It is also the only wild site where twin chimpanzees have survived to adulthood. On my recent visit to Gombe, I had the good fortune to see the twins and their daughters making and using tools to fish for termites.

Back in 2002, I remember following a large group of chimps in the Kasekela community, on the narrow trail climbing the steep path above Kakombe Valley, heading south to Mkenke Valley. It was Mabungo season and the chimps were feasting on fruits from the different kinds of Mabungo vines, especially Mabungo Makubwa (Big Mabungo) and Mabungo Madogo (Little Mabungo). The chimps traveled single file down the narrow trail. In the midst of the rainy season, everything was lush, green, and wet. The last chimp in the line was Gremlin, carrying her twins, Golden and Glitter, on her back. Sometimes their older sister Gaia would help mom by carrying one of the little twins. Gaia’s help is probably one reason that Golden and Glitter survived to adulthood — the only known pair of wild chimp twins known to have done so. Even with this help, though, the twins slowed Gremlin down. Being new to Gombe, struggling with the hikes up and down the hills, I was quite happy walking behind them, grateful for a chance to rest a little while watching these little girls play.

Amri collecting data on the twins, Gitter and Golden, and their babies, Gossamer and Glamour.

Amri collecting data on the twins, Gitter and Golden, and their babies, Gossamer and Glamour.

Now Golden and Glitter are all grown up.  Female chimpanzees usually leave the group of their birth and join a new one, to avoid mating with their brothers, uncles, fathers and such. At Gombe, though, about half of the Kasekela females stay in their natal group, probably because the dispersal options are limited: Mitumba is small and crowded, while Kalande is big but less forested (so less food) and has too few adult males.  So Golden and Glitter have stayed in Kasekela, as did their mother Gremlin.

We don’t know if Gremlin’s mother Melissa was born in Kasekela or if she immigrated from elsewhere. But now that Golden and Glitter have babies of their own (Glamour and Gossamer), we have four generations of G-family girls in one community. Their older sister Gaia has also stayed in Kasekela. When all the G-family moms and babies get together, it’s more like a baboon matriline than a typical chimpanzee group of unrelated females. This concentration of female kin might have some interesting implications for social behavior. Maybe all these related females will gang up on other females to control access to the best home ranges? They do seem very well established in Kakombe Valley, the best, most productive valley in Gombe in terms of chimpanzee foods.

Glamour, who just like her mother Golden, has a white spot on the top of her head. (11 June 2014)

Glamour, who just like her mother Golden, has a white spot on the top of her head. (11 June 2014)

This June, in between visits to the Kalande and Mitumba communities, I was able to spend some time following the twins and their daughters.

They spent much of the morning fishing for termites. Usually there’s more termite fishing in the wet season than this time of year, the early dry season, but perhaps the recent rains had softened up the mounds enough to make it easier for the chimps to stick in their termite fishing tools: wands made of grass or sticks, stripped of leaves to make slender probes.


Golden eating termites from her fishing wand.

Golden standing quadrupedally and holding her wand in her mouth. (11 June 2014)

Golden standing quadrupedally and holding her wand in her mouth.
(11 June 2014)

Jane Goodall’s discovery that chimpanzees make and use tools to fish for termites was one of the key findings that made Jane and Gombe famous. In The Descent of Man, Darwin argued that the making and using of tools originated after the evolution of bipedalism: walking on two legs freed the hands for manipulation, rather than transportation. It was therefore a surprising discovery that these knuckle-walking forest apes regularly used their hands, not just for walking and climbing, but also for making and using what has turned out to be a large variety of tools.

Tools increase access to important foods that would not otherwisebe available. Termites, for example, are rich in fat and protein, nutrients that are important but not well supplied by the mainstay of chimpanzee diet, ripe fruit.

Golden eating termites from her hand. (11 June 2014)

Golden eating termites from her hand.
(11 June 2014)

Tool use also increases the value of social learning. Termite fishing is a skill that takes years to learn properly, and kids mainly learn how to termite fish from watching their moms. As Elizabeth Lonsdorf elegantly showed with her studies of termite fishing at Gombe (in which Gremlin and the twins figured prominently), girls learn to termite fish faster than boys, probably because boys are too busy playing rough-and-tumble games.

Once cultural learning is established, a whole range of new subsistence strategies can be acquired that any one individual would never think to invent on their own.

Darwin was probably right that being bipedal helps with making and using tools. Chimpanzee hands are long, with curved fingers and short, weak thumbs. Australopith hands are much better suited for both the precision grip and the power grip. They must have had a much broader range of tools than chimpanzees: sticks for digging food and hitting rivals, stones for smashing food and throwing at enemies. But the discovery of tool use and material culture in chimpanzees suggests that these practices may have already been present in our common ancestor with chimpanzees, predating the origin of bipedalism — and perhaps providing increased selective advantages for individuals in those populations that first started standing bipedally a bit more than usual.

Imani standing bipedal to feed. (10 June 2014)

Imani standing bipedal to feed.
(10 June 2014)

Deus and Ramba looking out over Mitumba valley.


On Thursday, 12 June, Deus, Rebecca and I visited the Mitumba community in the North of Gombe.

Gombe is one of the few sites where researchers can study neighboring chimpanzee communities. At most sites, researchers focus on a single study community, and don’t know very much about the neighbors. This was the case at Gombe for many years, but since the Mitumba chimpanzees were habitatuated in the 1990s, we have been able to follow chimpanzees from two communities simultaneously. And now, with monitoring of the Kalande chimpanzees, we can track the movements of nearly every chimpanzee in the park.

The prospect of studying intergroup interactions from both sides of the event is what led me to start working at Gombe, and has been a focus of my research ever since. Deus has played a big part in this, as he collected data on the Mitumba chimpanzees, first as a research assistant on the intergroup relations project, and then as a PhD student.

When I first started working at Gombe, we worried that males from the larger, more powerful Kasekela community would kill the remaining males from Mitumba and take over their range. And sure enough, soon after I started working at Gombe, the young male Rusambo was found dead, with severe wounds, the day after Kasekela males traveled deep into Mitumba’s range (Wilson et al., 2004).

Edgar keeping a close eye on Flirt

Edgar keeping a close eye on Flirt

However, since then, the Mitumba males have held on, and even seem to have expanded their range a bit. And while intergroup incursions from Kasekela have continued, including the killing of the young infant Andromeda (Wilson, 2013),  it is the Mitumba males who have proved a greater threat to themselves. Mitumba males Edgar and Rudi killed their former alpha male, Vincent, in 2004. Soon after, the young male Ebony was found dead. Since then, Edgar and Rudi have fought bitterly and Rudi has disappeared. Edgar seems determined to keep Mitumba for himself, as if he were a gorilla silverback.

When we arrived in Mitumba, we walked up the steep, narrow valley of Mitumba stream. Gnarled old Mgwiza trees grow along the stream banks, and Lusieno trees tower overhead.


Flirt climbing down from her feeding tree.

Flirt climbing down from her feeding tree.

We found chimps close to the stream. Edgar followed Flirt closely. She had a full swelling and he clearly wanted to keep her all to himself. Flirt is one of Fifi’s daughters. She was born and raised in Kasekela. She was orphaned when her mother died in 2004, but managed to survive, spending much of her time with older brother Frodo. Flirt is one of the very few chimpanzees I ever saw Frodo groom.

After Flirt reached sexual maturity, she did what female chimpanzees usually do:  transferred to a new community. With Edgar showing so much interest in her, maybe she will conceive an infant soon.

Young male Apple followed them from a distance.  Apple is one of the2014-06-12 Apple sitting in tree A rising generation of Mitumba males, along with Kocha and Ramba. If these boys survive to maturity, then Mitumba may have a chance at keeping Kasekela at bay and maintaining Mitumba as a viable community. But with Edgar’s track record of attacking other males, maybe he won’t let these young competitors survive. If Edgar continues killing all the young males, his line may end in a Pyrrhic victory: eliminating not only his competitors, but his only allies against the mighty Kasekelans.

After coming down from the trees, the Mitumba chimpanzees soon climbed up the steep slide of the hill, giving us a chance to experience some classic Mitumba chimp viewing: crawling on hands and knees through vine tangle.


Nyamagoma Valley viewed from Lake Tanganyika.


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.





Freud eating termites 
(02 Nov 2006)

Isotopes and Isoptera

My main goal in visiting Gombe this trip was helping my graduate student, Rebecca Slepkov Nockerts, get started with her project on the stable isotope ecology of chimpanzees and baboons at Gombe.

Over the past couple of decades, stable isotope studies have revolutionized the study of the diets of human ancestors.

Isotopes are variants of chemical elements that differ only in the number of neutrons. For example, carbon has three naturally occurring isotopes, of which Carbon-12 (12C) is the most common. All carbon atoms have 6 protons – that’s what makes them carbon atoms, and not some other element. 12C has 6 protons and 6 neutrons, and is stable – each atom can last for billions of years. Carbon-14 (14C) is a radioactive isotope of carbon. It has 6 protons and 8 neutrons – which makes it unstable. It gradually decays, turning into Nitrogen-14 while spitting off an electron and an electron anti-neutrino. By geological standards, 14C  decays relatively quickly, making it useful for dating objects containing carbon that are up to about 60,000 years old.

The third naturally occurring isotope of carbon, 13C, has 6 protons and 7 neutrons, and is stable, though  much less common than 12C. For the most part, chemical reactions  involve interactions among electrons, and to some extent protons. Neutrons don’t get involved. As a result. 13C behaves chemically almost exactly like 12C. However, in some reactions, the slightly different mass of the heavier isotopes can make a difference. For example, in photosynthesis, molecules containing 13C move more slowly, because they are heavier, and end up in different proportions in the final product.

As it turns out, several different major groups of plants use different mechanisms of photosynthesis, which produce distinct isotopic signatures. Especially important in paleoanthropology are C3 plants (most plants, including most forest species) and C4 plants (certain plants adapted to hot dry climates, including many tropical grasses and sedges).

Unfortunately, all of these different numbered C’s quickly get very confusing! But the main thing to remember is that C3 = forest, C4=grass.  Chimpanzees mainly eat C3 forest plants. Even in dry woodlands, chimpanzees eat mainly forest plants: fruit, seeds, flowers and leaves from trees, vines and shrubs growing along rivers and streams. In contrast, baboons eat more C4 plants – especially grass seeds and corms. Similarly, stable isotope studies of fossils have found that early hominins ate mainly Cplants (and/or animals that ate Cplants), whereas later hominins at more C4 plants (and/or animals that ate C4 plants).

However, all of these inferences about hominin diet depend on some assumptions about how different tissues reflect diet. Unfortunately, studies comparing hominin isotope signatures to those of living species usually use different tissues. Studies of fossils usually use tooth enamel, which is extremely stable and thus is thought to maintain a good record of the living animal’s isotope signature for millions of years after death. Studies of living primates, however, usually use tissues that are easier to obtain, such as hair and feces, because it is hard to get tooth enamel from living animals (which are generally busy using their teeth). We therefore don’t know nearly enough about how diet translates to isotope signatures across these different tissues in living species. This is what Rebecca plans to find out.

Freud eating termites  (02 Nov 2006)

Freud eating termites
(02 Nov 2006)

The long-term study of chimpanzees and baboons at Gombe brings together the key pieces needed for this study: expertise in identifying and collecting the important food species, long-term records on diet, and skeletons from known individuals. For example, we have a lifetime of data on chimpanzees like Freud, pictured here in November, 2006 eating termites.

Rebecca and Deus examining the bones of Freud the chimpanzee

Rebecca and Deus examining the bones of Freud the chimpanzee

Freud recently died, at nearly 43 years of age (making him one of the longest lived Gombe males). Thanks to concerted efforts over the years by people at Gombe Stream Research Centre, the skeletons of Freud and many other well known individual chimpanzees and baboons have been preserved. Thanks to a lifetime of data on these individuals, we know a lot about what they have been eating. This comprehensive data on individuals will provide an unparalleled amount of detail for matching up diet to isotope signatures of different tissues.

It is particularly interesting to look at chimpanzees and baboons at Gombe because these two quite similar species differ somewhat in their diets in ways that parallel some differences between early and later hominins: baboons eat more grass than chimpanzees, just as later hominins appear to have eaten more grass (and/or grass-eating animals) than earlier hominins.

Rebecca and baboons collecting grass samples

Rebecca and baboons collecting grass samples

We are working together with Carson Murray and Rob O’Malley, who are conducting a nutritional study of chimpanzees. Both the nutritional study and the isotope study need foods to be collected, so we will work together to collect foods and share samples.

Rob did his PhD work at Gombe, studying insectivory by chimpanzees. Chimpanzees and baboons both eat a wide range of insects at Gombe.

Termites emerging from the nest

Termites emerging from the nest

On our first day in the field, we were lucky to catch an emergence of flying termites (“kumbi kumubi” in Swahili). These members of the infraorder Isoptera are one of the most important insect foods, not only for chimpanzees and baboons, but also many birds, monitor lizards, and even people.

Rebecca and Rob collecting termites.

Rebecca and Rob collecting termites.

We also found a nice column of Dorylus army ants (“siafu” in Swahili).

siafu jaws

Column of army ants showing off their jaws

Army ant soldier biting Rob's thumb.

Army ant soldier biting Rob’s thumb.

From an isotopic perspective, insects like termites and army ants may be interesting mainly for another isotope, Nitrogen, which provides information about where an animal gets its protein from. The higher the animal’s trophic level (the higher it is in the food chain), the more enriched its tissues are in the heavier Nitrogen isotope, 15N. It will be interesting to see whether chimpanzees and baboons at Gombe differ in their Nitrogen isotope signatures, and whether the isotopic signatures of individual chimpanzees relate to how much meat or insect matter they ate while alive.

At the night meeting, Rob and Rebecca explained their projects to the chimpanzee field staff. Rob talked about nutritional differences that he had found between ants and termites. I noted that “even people like to eat termites, right?” The field assistants responded with many people talking at once. The general consensus: “We like to eat termites, yes, but we like locusts even better!”

And I have to agree. Termite sauce with mushrooms is okay but seems a bit buggy to me, whereas fried locusts quite tasty.

Kigalye 20140604

Return of the Trees

04 June 2014

Gombe National Park is pretty remote. It is in the northwest corner of Tanzania, on the shores of the world’s longest and second deepest lake, Tanganyika. From the lakeshore at Gombe, you can see the hills of Burundi to the north and the mountains of Congo across the lake. It took me several days of travel, by train, plane and boat, to get to Gombe from our current home in France.

The research station at Gombe is only 22 km (14 miles) north of town, but because Gombe is surrounded by steep hills, you can’t drive there. Instead, we travel by boat, which usually takes 1.5 to 2 hours, depending on the conditions of the lake. The lake is often calm in the morning, but as the air heats up in the afternoon the lake gets choppier, until early evening when (usually) it starts to calm down again.  We left town at 2:00 pm, with a heavily laden boat and rough water.

Loading up Gombe boat






Having been away for two years, the biggest change I noticed was on the hills above the lakeshore villages. When I first visited Gombe in 2001, the hills outside the park were bare. Fields of cassava and beans were planted on slopes that seemed much too steep for agriculture. Red earth showed from erosion scars, including one in Mtanga village where a landslide in January 2001 killed 13 people.

Here’s a picture of Kazinga village, right at the southern boundary of the park, in August, 2005:

Kazinga Ridge 20050809




The park boundary runs along the crest of the hill, and apart from one big green mango on the ridge in the foreground, the trees end at the park. Just about everything on the slopes outside the park has been cut for firewood.

Kazing Ridge 20140604




In contrast, here’s how the same ridge looks now. It’s early dry season so the grass is greener, and thus makes the contrast seem even starker. But even taking this into account, what surprised me was seeing lots of trees on the slopes outside the park. Where the forest used to end abruptly at the park border,  now a blanket of forest drapes over the ridge, extending down towards the village. There aren’t trees everywhere, but even in Gombe the forest cover is intermixed with woodlands and grasslands, depending on the terrain and soil conditions. But that there are any noticeable trees at all outside the park is striking. The Jane Goodall Institute’s reforestation project really seems to be working.

It wasn’t just Kazinga village, either. Passing by many of the lakeshore villages I was struck at the contrast:  steep hills were now blanketed in green trees instead of bare red earth. The photo at the top of this blog post is Kigalye village, which has an especially extensive forest reserve. The trees are coming back.

After I got to Gombe, Lilian Pintea showed me satellite images that confirmed what I had seen from the lake. Not just along the lakeshore, but extending all along the crest of the rift escarpment, trees were coming back. This was the interconnected network of village forest reserves that had been promised in the Greater Gombe Ecoystem project. It really is happening.

The deforestation of the village hills was a classic Tragedy of the Commons. The trees provide many public goods. Their roots hold the soil in place, preventing erosion and landslides and protecting the watershed so important for the streams, the main source of drinking water for the villages. The trees provide wood for cooking fires, furniture, boats, musical instruments and traditional carvings. Many of the trees produce fruit eaten not only by animals such as chimpanzees and baboons, but also by people. Their flowers enable bees to make honey. The leaves of the trees shade the ground, slowing evaporation, helping the soil retain moisture. But because the trees are common property of the village, as the human population grew, people cut the trees faster than they could grow back. Soon the villages suffered the public costs of deforestation: erosion, landslides, fouled drinking water, lack of wood for fuel and lumber, and the disappearance of plants valued for traditional medicine.

In 1994, the Jane Goodall Institute started the Lake Tanganyika Catchment Reforestation and Education Program (TACARE). Twenty years later, with help from many outside sources, including the Nature Conservancy and USAID, the project really does seem to be succeeding.

Will the project be a success in the long term? That really depends on the people living in the villages, and whether, as the years go by, they perceive the forests as providing net benefits to them. There will undoubtedly be cases of human-wildlife conflict. Animals living in the forest reserves may raid crops; and people might hunt the animals. As trees grow bigger, there will be strong temptations to cut the trees with valuable timber, and decisions will need to be made at the village level about how to manage these resources effectively. But seeing these trees growing has given me hope that these are solvable problems.

Ferdinand, alpha male of the Kasekela chimpanzee community in Gombe National Park, looking smug.

The Declining Effectiveness of Violence

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!


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.

Locations of ape study sites

Solving the origin of a major malaria parasite

A recent study by Beatrice Hahn and colleagues, published in Nature Communications, has solved a major puzzle about the origin of one of the parasites that causes malaria in people worldwide: Plasmodium vivax.

Malaria is one of the world’s deadliest diseases, killing perhaps a million people each year. Most of the people who die from malaria are in Africa, and most of them children. In areas where malaria is common, adults often have a degree of resistance to the disease, but still get sick enough now and then to miss many days of work, suffering from agonizing aches, fevers and chills. Even though most victims are children, many adults die as well, especially when their immune systems are weakened by other infections. Malaria thus has huge economic costs and has been cited as one of the main drags on economic growth for many tropical nations.

Malaria has had a huge impact on human history and evolution. Malaria is one of the major reasons that Africa resisted European colonialism for so long. Europeans visiting Africa died in droves until the discovery that a drug extracted from the bark of the South American cinchona tree, quinine, protects against malaria. Quinine is fairly awful stuff: when I took it to fight a particularly bad malaria infection, it caused vomiting and a painfully loud ringing of the ears. From the mid-20th Century on, more effective anti-malarial drugs have been produced, which have helped many millions of people survive this terrible disease. Visiting and working in the tropics for business, tourism or, say, field primatology, would be a lot more dangerous without these drugs.

Before the discovery of such drugs, and for the many millions of people in poor countries who still don’t have adequate access to them, malaria has served as a powerful source of selection pressure on human populations. Because malaria is so deadly, human populations with long exposure to the disease have evolved a number of different defenses.

Malaria was originally thought to be caused by the “bad air” (Italian: “mala aria) of swamps and marshlands. It is now known to be a group of similar disease caused by several different species of single-celled protozoans from the genus Plasmodium.  Plasmodium falciparum is the most deadly, and the most common in Africa. Plasmodium vivax is more common in Asia.  Because these parasites are different species, and only distantly related, tricks that work to defend against one species of parasite may not work agains the other. 

The most famous  anti-malarial adaptation is sickle-cell disease, which is caused by a single small change to a gene for hemoglobin, the protein that carries oxygen in red blood cells. This change changes the shape of the hemoglobin molecule.

Sickle cells in action. From:

Sickle cells in action. From:

Red blood cells are packed full of hemoglobin, and if cells have only the abnormal hemoglobin, they become abnormally curved (shaped like a sickle or a crescent moon). People with one copy of the gene for sickle-cell disease have higher resistance to Plasmodium falciparum.

People with two copies of the gene, though, have sickle-shaped that cells get stuck going through narrow capillaries, causing all sorts of problems, which shortened life expectancy before the development of modern medical treatments.

Falciparum malaria is such a dangerous  disease that having improved resistance more than offsets the risks of having children whose lives are shortened by inheriting two copies of the gene.

Nonetheless, sickle-cell trait seems a rather clumsy solution to the problem. Kind of like using hand grenades to protect yourself from tigers. The grenades can stop tigers fine, if you can throw them far enough. But if you don’t throw them far enough, they blow up too close and kill you instead. Perhaps sickle-cell is an emergency stop-gap measure that evolved too recently for all the kinks to be worked out yet.

A seemingly better solution to this sort of problem is the Duffy-negative trait, which provides resistance to a different species (Plasmodium vivax), with little apparent cost to people who have the trait.

To understand the tricks that have evolved to defend against different species of Plasmodia, it is useful to know something about the life cycles of these parasites. These life cycles are complex and involves different stages of sexual and asexual reproduction in various organs of different hosts, including the human liver, human red blood cells, mosquito guts, and mosquito salivary glands.

Malaria parasite life cycle. From:

Malaria parasite life cycle. From:

The malaria life cycle is a complicated solution to problems of replication, sex, and dispersal of Plasmodium genes. In most animals that we are familiar with, such as ourselves, individual organisms do the major work of replication, sex and dispersal. As individual organisms, we accomplish these goals by mating, raising kids, and sending them off to college, for example.

Malaria parasites have found ways to outsource most of this work to other organisms. To replicate, they turn human hosts into giant malaria factories, turning red blood cells into production centers that burst, releasing newly produced parasites into the blood stream, infecting new red blood cells, in an exponentially increasing production system that destroys millions of the host’s red blood cells. This is the part of malaria where the human host feels weak and miserable and suffers from alternating fevers and chills.

Most of this replication phase is asexual: making millions of copies of the same thing. This works fine within a single host, but if you want your babies to survive in the cruel and variable outside world, you need to boost their chances by introducing variation into their genes through sex. So towards the end of the cycle, the parasites start making male and female versions, the gametocytes. When mosquitoes suck the blood of an infected host, they suck up these gametocytes, which can then have sex with gametocytes picked up from other hosts. The offspring of the gametocytes then infest the mosquitoes gut, eventually sending sporocytes to the salivary glands, so they get injected into the next person the mosquito bites, starting the cycle over again. The mosquito thus serves as both a malaria parasite dating service and dispersal system. Kind of like college.

Anyway, a key part of the malaria parasites life cycle is getting into the host’s red blood cells. To do that, they use specific proteins on the surface of the blood cell, which serve to transport certain chemical signals across the cell membrane. Plasmodium vivax parasites use one specific kind of protein, the Duffy antigen receptor, to force their way into human red blood cells. In much of Africa, the indigenous people don’t have this receptor. There is thus no way for P. vivax to infect them. People who don’t have the Duffy antigen receptor may suffer some costs, such as increased susceptibility to asthma, but these costs don’t seem to be anywhere near as high as those imposed by sickle-cell trait. And of course they are much less than the costs of dying from malaria.

The African distribution of the Duffy-negative phenotype has been a puzzle, though, because P. vivax is very rare in Africa. The conventional wisdom has been that P. vivax evolved in Asia. How could a parasite that evolved in Asia, and is rare in Africa, select for parasite resistance in Africans? This would be as puzzling as if people in Africa were all born with some sort of inherent immunity to tiger attacks, even though there are no tigers in Africa.

Beatrice Hahn and her team have solved the problem by collecting poop from thousands of apes across Africa. I played a very small part in this study, by overseeing poop collection for a while at Gombe.

Humans are apes, and many diseases that infect humans can also infect other apes, or (like in the case of HIV) originally came from other apes. Malaria is no exception.  On a molecular scale, we are so similar to chimpanzees and gorillas that the  tricks pathogens use for getting into human cells often work for these cells in other apes as well.

Beatrice Hahn’s team has been collecting fecal samples from apes all across Africa as part of a study looking into the origins of HIV-1, the cause of the global AIDS pandemic. It turns out that the same samples, and same molecular methods, that are so useful for studying HIV, are equally useful for studying all sorts of other things that live inside humans and other apes, including other viruses and gut microbes.

Locations of ape study sites

Locations of ape study sites

It turns out that when apes are infected with malaria, they shed some of the malaria DNA out with their poop. Take some poop, put it in a jar of RNAlater, and you can recover all sorts of fascinating genes, including malaria genes.

(When Jimmy Fallon and Justin Timberlake visited Gombe some years ago, they seemed amused by all of our poop collection and made up a song about it: “Poop in a Jar.” Disappointingly, though, they don’t seem to have recorded this one yet.)

It turns out that gorillas and chimpanzees across Africa, but not bonobos, have malaria parasites that genetically are very close to Plasmodium vivax. Compared to the gorilla and chimpanzee parasites, the human vivax is much less genetically diverse. All the human P. vivax belongs to a single branch of the much bushier tree of African ape P. vivax.ncomms4346-f2

It thus looks very clear that P. vivax evolved in Africa, not in Asia, from a plasmodium population that infects other African apes. People must have carried P. vivax with them when dispersing from Africa some 60,000 years ago. More recently, human populations in Africa evolved the Duffy-negative phenotype that proved so effective that P. vivax became extinct in Africa.

This study underscores the importance of evolution in human lives. Evolution happens fast, and human populations continue to evolve in response to our environments. The parasites that infect us evolve even faster. Evolution leaves traces in the genomes of every living organism that can be used to solve innumerable fascinating puzzles. This study highlights the power of molecular methods to answer important questions, especially when combined with field studies.





Via Ferrata cliff. With someone climbing on it.

Climbing the Iron Road

At lab meeting back in October, they asked me if I knew what Via Ferrata was. I had never heard of it before.  Turns out it’s from the Italian  for “iron road.” Charlotte drew pictures on the white board to show how it’s done: hiking in the mountains attached to a steel cable. That seemed fine to me – I like hiking, I like mountains, I like a nice view, and being attached to a steel cable sounded like a good safety measure. Much better than, say, rock climbing. That’s for crazy people.

Then Charlotte asked me if I had vertigo. Oh no, I said, I don’t have vertigo.

I think of vertigo as an irrational, paralyzing fear of heights.

Actually, I think of vertigo as having more to do with dizziness and nausea, but the French seem to use it to mean fear of heights.

In any case, this seems to me quite a different thing having a completely rational fear of falling from great heights and dying horribly on the rocks below.

Which, as it turns out, I have in abundance.

After several months of waiting for a day when everyone could go and it wasn’t raining, we finally embarked on our Via Ferrata outing. It was a lovely sunny day in early February. We drove north of Montpellier to the Via Ferrata du Thaurac, near the village of Ganges. We parked at base of a cliff along the gorges of the Herault River, the namesake of the Department where Montpellier is located.

(The name Herault is pronounced something like “Aygghho.” Just like it’s written, as far as the French are concerned.)

We each got a harness and a helmet. My helmet was a standard bicycle helmet. The harness was something you stepped into, with belts around your thighs and waist, a double rope with with carabiners at the end attached firmly to a loop at the front of the waist belt. This all seemed pretty reassuring.

Then we hiked up from the road onto a steep gravelly trail. This didn’t seem so bad. Then we got to a cave. Nice and cool and dark inside. Bats could be heard squeaking quietly deep in the cave. Michel, who studied the evolution of disease resistance in mosquitoes before turning his attention to human evolution, said that there were also female mosquitoes hibernating in the caves. They had gotten sperm from male mosquitoes in the fall. The males were long dead now. The females kept the sperm in storage, waiting for the weather to get warm enough form them to fertilize and lay their eggs and start a new generation of bloodsuckers.

Michel explained the basics of Via Ferrata: you attach both your carabiners to the cable. When you get to the end of the cable, unfasten one and attach it to the next cable before you unfasten your second carabiner. That way you are always attached to at least one cable with at least one carabiner. And wait for the person in front of you to move to the next cable before you attach, so that there is no more than one person per cable – so you don’t both fall and have your combined weight rip the supports out of the rock. That seemed easy enough. I had done a high ropes course with my son’s grade school class, so this all seemed familiar and doable.

Team in cave looking upThe first person in line fastened his carabiners to the cable running up the cave wall and began climbing up a series of steel rungs: u-shaped lengths of rebar hammered into the wall and secured with what looked like epoxy. He went up. Straight up. He crossed a gap above our heads, using rungs that seemed uncomfortably far apart. Soon he disappeared, going up a chimney towards the light at the top. One after another, the rest of the lab members followed, calmly climbing up into the abyss. (What’s the opposite of an abyss? Whatever that is.)

Ascending the chimney

Ascending the chimney

Then it was my turn. It took some time to get the hang of attaching and unfastening the carabiners, holding the rope to keep them close in hand. Michel followed along behind, providing helpful advice, patiently waiting for me to slowly crawl up and out of the cave.

It was terrifying. Completely terrifying. And exhausting. And it just got worse and worse. Climbing straight up inside the cave was sort of okay, because there were cave walls on all sides. But climbing up out of the cave into the open air revealed just how far we were above the river valley below.

It was a long way down.

I knew that as long as I kept attached to the cables, I probably wouldn’t die. However, it also seemed clear that if I did fall, I could get pretty banged up before coming to a halt. I imagined what it would be like to make the rest of the trip with a broken arm or leg. Which wouldn’t be fun.

Human evolution team looking out on the Herault Valley

Human evolution team looking out on the Herault Valley

But soon enough we were up and out. We stopped for lunch at a cave with great view of the wooded river valley. It was easy to imagine being here in the Paleolithic, when mammoths and cave bears wandered the valley. Prehistoric people used many of the caves in this area, and probably stopped at this very site to enjoy the same view. I thought of the Shamudoi, a tribe in Jean Auel’s Earth’s Children series who lived in mountain caves above the Danube River.

Climbing up

Climbing up

After lunch, we walked along a gentle path through the woods, which was pleasant enough, until we got to an even more terrifying series of climbs. Inside one cave, a sign pointed to a “Pont de singe,” a monkey bridge, which was a pair of steel cables crossing an open chasm high above our heads. You fastened your carabiners to the high cable and stepped out onto the lower cable. This actually wasn’t as bad as it seemed, because holding on to the upper cable was nice and secure.2014-02-04 14.29.53 Michel Jeanne Loic climbing A

We climbed higher and higher, and eventually found ourselves clinging to a cliff face high above the road where we had parked.

From time to time, visiting parks like Yosemite, I have looked up to cliff faces and seen the rock climbers and thought, “Those people are crazy. I have no desire to do that.” Now I was one of those people.

For much of the last stretch I climbed behind Julien, who had come up with the idea of doing the Via Ferrata in the first place. He loves to climb. He grew up in the mountains. He was having fun.

“This next stretch is easy,” he promised.

And it was easy, in that it involved moving horizontally rather than climbing. But psychologically it was completely terrifying.

I think of myself as reasonably fit, but it took a lot of strength to hold on and climb, and I was soon pretty weary. Being terrified probably didn’t help.

Fear of heights has become a classic example of an evolved psychological mechanism – one of the “modules” that evolutionary psychologists talk about. In a world with substantial gravity, it makes tremendous sense for heavy-bodied, wingless creatures like ourselves to be afraid of edges and heights.

For much of the 20th Century, associative learning theory dominated psychology. In this view, humans have no instincts, apart from a general-purpose associative learning instinct. Fear of heights is something we learn from bad experiences, such as falling from great heights. Starting in the 1990s, though, several studies looking in more detail at fear of heights found that prior experience didn’t explain the extent to which people experienced fear when exposed to heights. Studies also found that crawling infants and young animals of other species avoided moving across transparent surfaces that were completely safe but looked scary.

You don’t need to have fallen off of a cliff to find cliffs terrifying. Like many adaptive emotional responses, we may be unaware of fear of heights until we need it. Just thinking about the trip beforehand, I had no idea of the intensity of the fear that I would feel. This is similar to other evolutionarily important emotional responses, such as sexual desire, romantic love, jealousy, parental love, and grief. We experience these powerful emotions at key points in our lives, and they help guide us towards actions that, on average, make it more likely for us to propagate our genes. Unfortunately, while the passions may have evolved to promote behaviors that, on average, over evolutionary time, provide fitness benefits, they are often unreliable guides to behavior in specific cases, and they can sometimes prove paralyzing rather than helpful, or lead us to commit actions that we later regret.

Among the passions that have been proposed to be psychological mechanisms are those relating to violence and warfare: patriotism, xenophobia, hatred, revenge.

In a 1999 review of Michael Ghiglieri’s book Dark Side of Man, geneticist Richard Lewontin expressed doubt that aggressive behavior in humans is the result of psychological adaptations, based on his own experience of never having had such urges:

“Human males are described as being by nature rapists, murderers, warriors and perpetrators of genocide, one chapter for each. I begin to doubt my own species identity, having never engaged in, or fantasized about, any of these activities whether drunk or sober, asleep or awake. “

What if, however, the passions motivating violent behavior are like fear of heights: dormant until set off by a highly specific set of cues? Most of the time, I do not experience fear of heights, because most of the time I am not clinging to the edge of a cliff hundreds of feet above the ground. But when my brain detects the unusual set of cues associated with the ground being ridiculously far away, it sets off a whole series of powerful physiological and psychological reactions. Perhaps the passions that motivate people to do horrible things during wartime are like this: quiescent within each of us, never noticed unless wakened by a set of circumstances that in modern, peaceful, prosperous democracies, most of us are fortunate enough to never experience.

As far as I know, we don’t really know much about the details of the purported wariness of heights module. As with much of evolutionary psychology, we’re still very much in the black box phase of science: there is this black box that we call the “wariness of heights module,” that helps to keep us alive by making us avoid falling off edges. Exactly how it is represented in the brain, and how it develops, and how it relates to genes, remains unknown. We have a lot left to learn about the brain. But to me, it seems a vast improvement to be looking at the brain as a product of evolution, designed by natural selection to solve evolutionarily important problems, than to see it as an undifferentiated associative learning device.

Some people dislike evolutionary explanations for behavior because they think such explanations require that human behavior consist of inflexible responses triggered by simple stimuli. However, fear of heights seems to be a good example of a psychological response that is both powerful, and capable of being modified by personal experience. For example, during the course of the afternoon, my fear gradually subsided. I managed to calm down, move slowly and deliberately, without looking down or visualizing too vividly my widowed wife and orphaned children.

As with many adaptations, there also seems to be variation, both among individuals, and perhaps among populations as well.

View of the river and village below

View of the river and village below

Julien, raised in the mountains, seemed perfectly happy standing on the edge of the cliff, looking out at the spectacular view. I grew up in flat country.  Even though I have ended up spending a fair amount of my adult life following primates on cliffs and mountains, I was still much happier clinging to the rock face ten feet back from the edge.

As for populations, about 10% of New York steelworkers are Mohawk Indians, and some people have suggested that people from this tribe naturally have no fear of heights.

According to this article, ironworker Kaniehtakeron ‘Geggs’ Martin says, “They always often ask me if I’m afraid of heights… a lot of people are. I’m one of them who isn’t.”

Another possibility is that these Mohawk steelworkers feel the fear, but because their culture emphases courage and risk taking,  they don’t show fear. For example, according to this article, “Anthropologist Morris Frielich . . .  compares high-steel Mohawks to warriors who risked death and returned  with booty. Some anthropologists have also suggested that the risky work gave tribesmen a chance to test and display their courage.”

At one point near the end of the Via Ferrata, I thought I wouldn’t be able to make it any further. We had just crossed another monkey bridge across a chasm. To the left, down a gentle horizontal trail, someone was playing guitar and singing. Julien said I could take that trail and go out the easy way. Julien climbed up, but said there was only about 5 m of really hard stuff. I tried going up. About ten feet off the ground, the rock face bulged out, and it was there that you had to change carabiners to the next cable. I was tired, I couldn’t reach the next rung, and couldn’t get high enough to change cables comfortably. I climbed back down to rest and reconsider. Several other people went ahead of me.

Charlotte went on ahead, and hanging from the rock, called down to me, “Imagine that you have to save a beautiful princess!”

I gave it another try and made it up and over the bulge, and finally up over the top.

Which now has me puzzling over another evolutionary problem:

The appeal of putting ourselves in risky situations. Why do people willingly do such things? And why would they ever do it a second time?

And yet another evolutionary puzzle:

Looking back, I’m starting to think it would be fun to try again.

Via Ferrata cliff

Via Ferrata cliff

Infection Gangnam style

Is English a Virus from Outer Space?

Last week, I attended talks for the Society of Anthropology of Paris meeting here in Montpellier. This has been an interesting experience for many reasons. For one, the talks have shown some interesting differences in the politics of anthropology in France compared to the United States.

The society was founded by Paul Broca in May, 1859, six months before Darwin published the Origin of Species. Broca discovered the language-associated area of the brain that bears his name, and was the one of the first to study the Cro-Magnon fossils, discovered in France in 1868.

While the society carries the general name of Anthropology, it now focuses on Biological Anthropology. The talks were mainly what in America we would call archaeology: analysis of bones and food residues from historic and prehistoric graves and occupation sites. Interesting stuff, but a bit narrow in scope. Few talks focused on human behavior, apart from a session of evolutionary psychology talks Thursday morning. In contrast to the American Physical Anthropology meetings, there were no talks on nonhuman primates. Most strikingly, there was no sociocultural anthropology at all; they have different meetings. Apparently, the divide between quantitative, evolutionary anthropology and qualitative, interpretive anthropology is even more stark in France than in the US. It seems more like an old, nearly-forgotten divorce than the uncomfortable marriage-on-the-verge-of-separation that still exists in American anthropology.

Another interesting aspect of the meetings was the use of language. The audience was mainly French, so I expected all the talks and slides to be in French. One speaker, based in England but not a native English speaker, gave her talk in English, but most of the language on her slides was French. The other speakers spoke in French, but for many of the talks, some or even all of the slides were in English. They frequently used English for technical terms, or when citing the title or findings from papers published in English. This was all very typical of what I have been seeing in departmental seminars at the University of Montpellier. The audience is mainly French, and most of the talks are in French, but visiting speakers usually give their talks in English, which everyone in the audience seems to understand reasonably well. And even when the speakers are French, their slides are sometimes entirely in English.

Before coming here, I had the impression that the French were highly protective of their language. They have laws requiring the use of French in commercial communications. They have L’Académie française, which tries to keep the language contaminated from foreign words like “le sandwich” and “les airbags.”  Government agencies strive to come up with replacements for English words like “buzz,” “chat,” and “newsletter.” And in a recent study, France ranked right at the bottom of the heap of European countries for English language proficiency. And there’s a stereotype that the French are hostile towards people who can’t speak French properly (meaning most of us Americans).

In contrast to what I expected, though, most of the people I’ve encountered seem to have a very positive attitude towards English. People who know some English are eager to practice it. It’s not like northern Europe, where almost everyone in the cities seems to speak perfect English, but enough people speak English that in many situations, I have to make an effort to keep using French. The books in the lab library are mainly in English. My French colleagues read and publish their papers in English-language journals. Lab meetings and social interactions are mainly in French, but everyone can switch to English when needed (like when I give up in my struggle to explain something in French, which often happens). Outside of academia, English words and phrases occur in ads and on signs, and English-language songs dominate the radio (which is required by law to have 40% of songs in French during prime hours).

On a global scale, French has fallen dramatically from its 19th Century peak as a major language of empire, diplomacy, learning and culture. The percentage of American and British students studying French as a foreign language has dropped dramatically in recent decades. In much of North America, place names from Indiana (La Fontaine) to Minnesota (the redundantly named Mille Lacs Lake) reflect a long-lost empire, where French has been reduced to a declining minority language in Louisiana and even in Canada, where the proportion of native French speakers has dropped to 22% of the population. Even in Africa, where France had a vast colonial empire, French may be losing ground compared to other languages. In formerly French North Africa, Arabic competes with French for status as the primary language. South of the Sahara, French is still widely used as an official language, but Rwanda dropped French in favor of English, both in protest to French actions during the Rwandan genocide, and as part of an effort to build closer ties to the Anglophone East African Community. English is an official language of Africa’s most populous country (Nigeria) and the biggest economy (South Africa), and is the language of higher education in Africa’s second most populous country, Ethiopia, even though Ethiopia was never part of the British Empire. In Asia, English is widely spoken in South and Southeast Asia, including the second most populous country on the planet, India, whereas French has a small and declining number of speakers in former French Indochina.

In the thousand year-old rivalry between English and French, English seems to be gaining the upper hand.

Which has me wondering: what makes a language expand or contract? Does it mainly have to do with features outside the language, such as politics, demography, military conquest, and migration? Or does it also depend, at least to some extent, on features of the language itself?

I remember a night more than twenty years ago, during my first field season in Africa, studying baboons in Kenya. Gathered around the dinner table with American and Kenyan researchers, eating by the warm glow of kerosene lanterns, conversation turned to why English was so widely spoken. One of my American colleagues suggested that it was because English was so open to new words and ideas. Instead of trying to keep out foreign words, English readily adopts new words, like America adopts new immigrants.

I thought this was a funny thing to be saying in Kenya, where English was widely spoken not because the language is so open and friendly, but because it was the language of the British Empire, which colonized Kenya and much of the rest of Africa, as well as most of North America. The reason Kenyans and Americans had English as a common language had more to do with British seafaring, commerce, and military might than with any particular virtues of the language they spoke.

Similarly, all sorts of languages that might be hard for non-native speakers to learn have spread widely due to non-linguistic factors, such as the military might and demographic growth of their speakers. English speakers generally consider Russian, Chinese, and Arabic all hard to learn, but that didn’t stop these languages from spreading widely as their respective empires expanded.

All the same, thinking more about language from a Darwinian perspective makes me wonder whether, in the competition among languages, languages might change in ways that affect their relative competitive ability.

A language, like a biological species, has a life cycle, and is in competition with other languages. A language may spread widely and diversify, leaving numerous descendant languages, as Latin gave rise to the Romance languages, or Sanskrit to many modern Indian languages. Or it may shrink and die.

Growth or decline for languages occurs much the same way as it does for species: through births, deaths, and migration. Each time a child is born and learns her mother tongue, a new speaker is added to the language. If a language is no longer being transmitted to the young, but is only spoken by old people, the language will die with the last aging speakers.

Languages also migrate with their speakers. One reason English is spoken so widely is because seafaring English speakers established colonies around the world. In some of these colonies, English speakers became numerous and eventually swamped not only the native populations but also all subsequent immigrants. Some linguists call America a “language graveyard” because speakers of so many different languages come to America, only to have their children learn English and forget their mother tongue.

The total population of French speakers appears to be growing. In evolution, though, what really matters is relative growth rate. Genetic fitness, for example, is essentially a measure of relative growth rate of particular variants of genes (“alleles”) in a population. Alleles that have a high relative growth rate become increasingly common in the population, and may eventually reach fixation, present in essentially all members of the population. An allele, or a language, can become less common in the population if it is increasing at a slower rate than the population as a whole.

But unlike genes, language isn’t transmitted only from parents to offspring. Language can also be transmitted to completely unrelated people. In this way, a particular language is more like an infection.

As William S. Burroughs wrote and Laurie Anderson sang, “language is a virus from outer space.”

This is a thought-provoking image. Like a virus, a particular language is not part of the host’s own genome, but it uses the host to spread itself. However, it is wrong on two counts.

First, even though human language is an extremely peculiar and probably unique form of communication among earth species, invoking space aliens as an explanation is sort of the reverse of Occam’s razor: “among competing hypotheses, the hypothesis with the fewest assumptions should be selected.”

Second, even though language has some virus-like properties (it is can be transmitted from one person to another), it is really more like a plasmid than a virus.

Viruses are parasites that hijack the cellular machinery of other organisms to make more copies of themselves. But they usually don’t do anything to help the host, and in fact they often harm the host. A cold virus has been making the rounds of my family, and it has done nothing good for any of us. Instead, it lurks in our cells, churning out more copies of itself, and manipulates our bodies to ooze those copies out into the world to be spread to other people through coughing, sneezing, and running noses.

In contrast, at least as far as transmission is concerned, a language is more like a plasmid than a virus. Plasmids are little circular bits of DNA found in the cells of bacteria and other organisms.

Plasmids encode genes that provide handy tricks for the host, such as resistance to an antibiotic, or the ability to make a toxin. Plasmids can enable their hosts to live in what would otherwise be a hostile environment. Plasmids are useful to the host, rather than harmful, probably because of their mode of transmission: they can only be transmitted when the host reproduces (by dividing, in the case of bacteria) or when the host connects to another cell specifically to obtain new genes.

Like a plasmid, a language can do all sorts of useful things for its host. So much so that I’ve been making considerable effort to infect myself with a new one (French).  The infection is far from complete (and is progressing rather more slowly than I might have hoped), but it’s far enough along that I can do a number of useful things with it, like order coffee and chocolate croissants, or renew my commuter rail pass, or get a new inner tube for the wheel of my jogging stroller, all of which would be harder to do using only the infection that I inherited (English).

The idea of language as a virus, or plasmid, or other transmissible agent is closely related to the term “meme,” which Richard Dawkins coined in The Selfish Gene, to make an analogy between cultural and biological evolution. The word has caught on, happily, to refer to Internet pictures of LOLcats and such, which are memes in exactly the sense that Dawkins originally meant: little bits of information that are able to get themselves propagated, and which undergo mutations and evolve overtime in branching lineages, just as genes do. In this sense, a language is basically a big complex of memes.

In this view, the individual words in a language are memes. Like genes, they evolve, becoming more or less frequent in a population over time, and undergoing mutations, and sometimes becoming extinct.  Words compete with other words in the meme-pool.

The word computer, for example, is a Latinate word that came into English from French around 1646. At that time, the word “computer” referred to a person, not a machine: someone whose job it was to do calculations. Three hundred years later, when electronic calculating machines were invented, English speakers described the machines as “computers.” This sense of the word spread from English into a number of other languages, like Russian (kompyuter) and Swahili (kompyuta). But in France, the original home of the term “computer,” they instead use “ordinateur,” a word created in 1955 at the bequest of IBM France, because the term “computer” seemed “too restrictive in regard to the possibilities of these machines.”

So while languages have memes like viruses have genes, and like viruses they can be transmitted from one person to another, languages are usually useful to their host, rather than harmful. Why is that the case?

One reason might be the mode of transmission. A virus that is transmitted via saliva and snot is mainly interested in making its host produce lots of saliva and snot, and sneezing and smearing those fluids as widely as possible. The virus doesn’t share any genes in common with the host, and its reproductive success doesn’t depend on the reproductive success of the host. (Except for sexually transmitted viruses; though here, the interests of the host and virus still diverge, since the host doesn’t necessarily reproduce each time it has sex. A sexually transmitted virus benefits if the host lives long enough to keep having sex with more partners, but its own success doesn’t depend on whether the host actually reproduces successfully.)

In contrast, the surest means of language transmission is through the reproduction of the speaker. Languages take a long time to acquire (as I am painfully aware), and even though people say little kids learn languages quickly, it still takes years from them to learn their mother tongue properly, and from what I’ve seen in my own family, acquiring a new language is no trivial matter even when young. Because transmitting language from parent to child depends on successful raising of the child,  the interests of the language closely coincide with the interests of the host.

But unlike a host’s own genome, a language can be transmitted horizontally as well as vertically: from host to host, rather than just host to offspring. It is in this respect that a language is more like a plasmid than either a virus. Like a plasmid, a language is useful to its host, it is transmitted to the host’s offspring, and it can also be transmitted to other unrelated hosts.

Of course, languages aren’t exactly like plasmids. It’s just an analogy, and any analogy can be pushed too far. But to me it seems a helpful analogy for thinking about the relative growth rates of different languages.

In an environment full of a particular antibiotic, such as penicillin, bacteria that acquire the penicillin-resistance plasmid will survive and reproduce, whereas bacteria without that plasmid will die out.

Likewise, in a world where English provides access to information, jobs, and money, people will have a strong incentive to acquire English.

On balance, I would guess that most of the reasons for the success of English have little to do with any particular properties of English. English is not, of course, intrinsically a “better” language than French, or Swahili, or Basque, or any other language. All of these languages can be used to communicate any idea. Most of the current advantages of English have to do with the social and political environment, which depends more on the happenstance of the British Empire spreading English across the world and planting colonies in fertile places, and the resulting the wealth and power of the United States and its impacts on global commerce, popular culture, science and technology. Currently a huge factor must be frequency dependent selection. As English becomes more widely spoken, it becomes increasingly advantageous to know it. This produces a snowball effect, benefiting English at the expense of other languages.

Still, are there some linguistic features that have helped English become widespread? Has English itself evolved in ways that make it more contagious? Perhaps the early history of contact with other languages, like Brythonic, Old Norse, and Norman French, helped to eliminate some features that were harder for non-native speakers to learn (most aspects of gender and case, for example). Elimination of tricky features seems to have happened with other languages. Swahili, for example, emerged as a trading language between Africans speaking Bantu languages and traders from Arabia, Persia and elsewhere. Many Bantu languages related to Swahili have tones, but Swahili doesn’t, perhaps as a result of interaction with Arabic and other languages.

Perhaps the combination of Germanic grammar and Romance vocabulary helps to make English easier for speakers of these two major branches of European languages to learn.

And also, given that much of the innovation in science, technology, and other ideas happens in Anglophone countries, and is communicated in Anglophone channels, English is rich in vocabulary useful for talking about these new things and ideas.

But another way that English might help propagate itself is through the production of little bits of language that are highly infections in their own right: songs, books, movies, and the like.

Popular music, and music videos, seem especially virus-like. A pop song doesn’t provide obvious benefits to the listener. Instead, it exploits the listener’s sensory biases in ways that make the listener want to repeat the experience.

Take the music video for Gangnam Style, for example. I watched it many times.  I haven’t learned anything useful from it, except perhaps an explanation for why all the kids at the disco are dancing like they are riding ponies. This mainly Korean language video went viral, in part due to its catchy little hook of weird English.

In the book Plagues and Peoples, historian William H. McNeil argued that a key factor in history was the diseases carried by different peoples. The Eurasian landmass provided a massive Darwinian breeding ground for particularly nasty infectious agents, passed from domestic animals to people, and transmitted over thousands of miles of steppe by mobile horsemen. When Europeans first traveled to the Americas, they carried these highly infectious agents with them, with disastrous results for the Native Americans.

In a similar way, the vast Anglophone world serves as a global breeding ground for particularly infectious memes. I’ve talked with people who say they learned their English from listening to rap, or watching TV.

Perhaps official efforts to protect French actually serve to weaken the language, reducing its ability to resist infection, and reducing pressure on the producers of songs, books, movies and other cultural artifacts to be maximally infectious.



Isabella Rossellini with dolphins

Green Porno and Disgust

Isabella Rossellini is doing a show, Green Porno, in which she performs the mating behavior of a whole range of other species, such as honey bees and spiders. The show is based on a series of videos that she has been making since 2008.

Isabella Rossellini and friend.

Isabella Rossellini and friend.

Holy cow. These are awesome – and biologically accurate, in a whimsical, funny way. Rossellini clearly did her homework. But sexy? Not so much, I think. Rossellini herself says that though the bits are called “Green Porno,” “There is nothing porno about them.”

I teach a course on Sex, Evolution and Behavior, in which I occasionally illustrate key points with short video clips of the mating behavior of other species, from slugs to albatrosses. Not for titillation, mind you, but for education. In fact, while such video clips may be weird, or interesting, or comical, or gross, or some combination of these, they are pretty much never even remotely titillating. At least in my opinion. And my impression is that for most people, sex in other species is generally much more icky than sexy.

Which makes me wonder: why might this be the case?

The world is big, and has many kinds of people in it, and perhaps somewhere on the Internet there are sites for people who really do find the mating behavior of lobsters arousing. But I expect those sites are vastly outnumbered by sites depicting the mating behavior of our own species.

So why do we perceive sex in other species to be disgusting rather than sexy?

One possible explanation is that this disgust response is part of an evolved psychological mechanism that promotes mating decisions that enhance, rather than reduce, fitness. If we found slug sex really sexy, rather than disgusting, we might try mating with slugs, which (among other things) would be a real waste of mating effort.

If this hypothesis is right, that disgust at other species’ sexuality is a reproductive isolating mechanism, an adaptation to keep us from mating with the wrong species, then we should find the sexuality of species closely related to us to be particularly disgusting. After all, we probably couldn’t really mate with a slug even if we wanted to, but mating with something more closely related to us, like a chimpanzee, at least seems within the realm of possibility.

Back when the world had multiple species of humans living at the same time, such as our ancestors and the Neanderthals, interspecies mating would have been a real option. And studies of fossils and ancient DNA indicate that such matings did occur, at least on occasion. Given that hybrids can have various genetic problems, such as infertility, individuals are likely to have more offspring if they reliably mate with their own species, rather than some other species. And indeed, many aspects of animal behavior and anatomy appear to be related to species isolating mechanisms: courtship behavior, species-specific coloration patterns, and genitalia designed to fit like a lock and key, so that the parts only fit with the right partner.

So, what about this prediction, that if disgust is a reproductive isolating mechanism, we should find the sex of species closely related to us to be particularly disgusting? I don’t know of any formal studies of this, but from watching and listening to people’s reactions to monkeys at zoos, I get the strong impression that in general, people really do find monkey sex disgusting, as well as funny and embarrassing.

As a primatologist, I have seen lots of monkey sex: baboons, rhesus monkeys, chimpanzees, gelada monkeys, and so on. All these animals have sex in the open, in public, for everyone to see, so you don’t need to be a creeping pervert to see them going at it. In many cases, you would have to make a real effort to avoid it. And none of it, really, is very sexy, from a human point of view. In chimpanzees, mating is a furtive event that lasts six or seven seconds on average, which often ends with the female screaming and darting away from the male, as if she is terrified that he might beat her up. Which he might well do.

In my first field season as a primatologist, studying baboons in Kenya, I spent quite a bit of time looking at baboon bottoms. Not because I am particularly interested in baboon bottoms, but because (1) if you are following baboons, you’re going to see a lot of baboon bottoms, just that’s what you see when they’re walking in front of you, and (2) baboon bottoms display a whole lot of really valuable information about their reproductive state. You can tell whether a baboon is male or female, for example, just by looking at their bottom, even if they are just little kids. Baboons have a region of bare, tough skin going across their top of their bottoms that serves as a seating pad: the ischial callosities.

Males have a continuous seat pad surrounded by a patch of grey skin:

Back side of a male baboon

Back side of a male baboon









Whereas females have two separate pads, for the left and right cheeks, separated by the genital opening:

Female baboon at Gombe with bright red pregnancy sign.

Female baboon at Gombe with bright red pregnancy sign.







You can tell where a female is in her ovulatory cycle, as when a female is approaching her fertile time, the skin of her perineum swells up into a big pink sexual swelling, which looks extremely uncomfortable. And if a female is pregnant, the bare skin above her ischial callosities turns from grey to bright crimson.

When I was first habituating baboons (following them at a distance so they would get used to us and let us observe them at closer range), one afternoon we managed to get close enough to our group to see them resting on the face of the steep cliff where they would spend the night. Peering through my binoculars, I could see one female with what appeared to be a raw, festering sore by the base of her tail. As the weeks went by and the baboons let us get closer, I realized that this “sore” was just the bloody red pregnancy sign. It doesn’t look nearly so nasty when you are close enough to see that is not in fact a festering sore.

So during my ten months of following baboons around, I spent a lot of time looking at their bottoms, drawing pictures of their bottoms, taking notes of their bottoms to learn who was who and what their reproductive state was. At first, some features of baboon bottoms seemed kind of gross. I got used to that. And eventually I learned what sort of bottoms looked especially appealing to male baboons, by seeing who made special efforts to mate with.

Ahabazi grooming Ubergiji, who has a full sexual swelling.

Ahabazi grooming Ubergiji, who has a full sexual swelling.







But never in my loneliest days in the field did I find baboon bottoms sexy. Sorry babs, that just how it is.

On the other hand, many examples of hybrids exist. For example, as Kate Detwiler has documented, blue monkeys and redtail monkeys at Gombe and several other sites mate and produce hybrid offspring. My first experience studying primates involved a class project looking at the behavior of the hybrid offspring of a sooty mangabey and a mandrill: a mangadrill. So if disgust is part of a reproductive isolation mechanism, it clearly doesn’t always work.

Whether or not disgust is a reproductive isolating mechanism, it certainly plays a big role in regulating sexual behavior. Even within our own species, we perceive many categories of mating behavior as well, kind of gross. Or really gross. Little kids often seem to think that even kissing is pretty gross, much less the other things that grown-ups are rumored to do in private.

And much of the human disgust response makes sense from an evolutionary perspective. For example, various studies have found that women are considerably less interested in graphic depictions of mating than men are. Many men enjoy looking at graphic, impersonal depictions of anatomical function. Many women find that sort of thing disgusting. Instead, they prefer reading romance novels, or watching romantic movies, where sex occurs in the context of relationships developing between realistic characters. Or with vampires. Or werewolves. Whatever.

Is there a reproductive isolation mechanism at work here?

Is there a reproductive isolation mechanism at work here?







The emphasis is on the relationship first, anatomy second.

A recent example of this sex difference in action is the case of the politician Anthony Weiner, who sent pictures of his privates to women who were not his wife. One can imagine him thinking, “Hey, I’d love to have women send me naked pictures of themselves! Surely they would like me to do the same for them!” And maybe there are women who would like that. But I think this response by a blogger is more typical: “The truth is, guys, your ‘junk’ is one of the last things we want to see up close via digital or printed media.”

The Golden Rule, “Do unto others as you would have done unto you,” doesn’t work so well in cases where people have strong differences of opinion about what they would like to have done unto them.

And from an evolutionary perspective, this sex difference makes sense. If it is important to be choosy about mating, then being aroused by random sexual images would be counter-productive. In humans, women tend to be choosier than men. This makes sense, because men and women face much different costs from mating. A man who has sex with a random stranger might get the evolutionary “win” of impregnating her without having to do any work bringing up the baby. A woman who has sex with a random stranger may get stuck doing all the work. Thus for men, sex with strangers is an opportunity, whereas for women it is a risk, and best to be avoided. (Unless, for example, that stranger is so amazing that having his baby would be worth the trouble. Elvis, say, or Magic Johnson.) Disgust at random male junk may thus be an important mechanism guiding mating decisions that prove beneficial, at least on an evolutionary timescale.

Even for men, though, sex with strangers can be risky, if those strangers are infected with nasty diseases. So both sexes should be equally disgusted by anything that indicates such an infection, like festering sores.

In humans and certain other animals, including many bird species, sex often happens within a long-term relationship, rather than with random strangers. And just as in many birds and some mammals, like wolves, male humans do a lot of parental care. If a man has good reason to think his wife is mating only with him, and is uninterested in mating with other men, then he will have good reason to believe that her children are his, and that he should invest in them, by bringing them meat, or carrying them around, or changing their diapers, or whatever.

In contrast, among chimpanzees, males and females both mate promiscuously. Males don’t provide any parental care (apart from defending a group feeding territory), so females are always stuck doing all the work of parenting. However, males sometimes kill babies of females that they haven’t mated with. So females have a strong incentive to mate with all the males of her community, to convince them all that they might be her baby’s daddy.

Given this difference in mating strategies, if female chimpanzees used smart phones, they might like nothing better than to receive photos of male chimpanzee private parts. I suppose that’s an experiment that could be done.

Recently, disgust has gotten lots of attention as one of the key moral emotions. In college, I sat in on J. Z. Smith’s Religion in Western Civilization class.   In talking about Leviticus, the Biblical book of rules, many of which seem baffling beyond belief, Smith argued that “the complaint of the writers of Leviticus was not, ‘God, why have you made me such a sinful being.’ No, it was more like, ‘Why have you made me with so many holes?’” Humans leak all sorts of disgusting substances from their various orifices, and many of the rules of Leviticus involve proper regulation of these fluids.

Smith seemed to think that these rules involved a fairly arbitrary sense of disgust, rooted more in aesthetics than reason. For example, he argued that Jewish dietary law forbade eating pork because pigs are disgusting animals. They wallow in filth, they eat trash, we shouldn’t incorporate such filthy animals into our bodies. Smith argued that the argument that such laws protected Jews from trichinosis was an invention of 19th century Reform Jews who wanted to find more rational foundations for traditional beliefs.

More recently, Paul Rozin and others have argued that rather than being arbitrary, disgust really is rooted in evolutionary logic: many things that we find disgusting are dangerous: rotting meat, maggots, festering sores, snot, feces and the like can all transmit pathogens. If we eat such things, or even touch them, they can make us sick, or dead. From an evolutionary perspective, it makes sense to have emotional mechanisms that make us avoid such potentially dangerous substances. In this view, feelings of disgust originally based in avoidance of pathogens have expanded to provide one of the main foundations of moral feeling.

A moral emotion like disgust can guide behavior more quickly, and more reliably, than rational arguments. If we had to stop to think and debate amongst ourselves whether rotting carcasses, for example, were safe to touch, we might pick them up and expose ourselves to all sorts of pathogens before we have persuaded ourselves that maybe that’s not such a good idea. The same way with many moral actions: if people think an immediate, gut response of disgust to pedophilia, or rape, or murder, they will be inhibited from even giving it a try.

Disgust seems to involve both learned and innate components, and develops gradually as children mature. Toddlers, for example, seem to find nothing disgusting. But pretty much everyone eventually grows up to find rotting meat and vomit disgusting. People seem to have a natural disposition to develop feelings of disgust towards things that carry a strong risk of infection.

More recently, Jonathan Haidt and others have argued that disgust is at the heart of the six moral foundations or dimensions: care/harm, fairness/cheating, liberty/oppression, loyalty/betrayal, authority/subversion, and sanctity/degradation. In this view, disgust is involved mainly in the sanctity/degradation dimension.

Much of the current political debate about gay marriage involves tension between these different moral foundations. People who emphasize the first three moral dimensions see gay marriage mainly in light of care (we shouldn’t cause emotional harm to people by denouncing their private life choices as sinful), fairness (it’s only fair that people who love each other should be allowed to marry), and liberty (people should be free to be who they are and love who they love). People who emphasize the other dimensions see gay marriage mainly as an issue of authority (scripture says it is wrong) and sanctity (heterosexual marriage is a sacrament; homosexual marriage is wrong). Thus, people on both sides of the debate are morally outraged by the arguments of people on the other side.

And from an evolutionary point of view, an aversion to same-sex mating seems to make a certain amount of sense: such mating doesn’t produce offspring. But it turns out that evolution is more complicated than that. For some species, homosexual mating is not a preference or orientation for a portion of the population; it’s obligatory. For example, New Mexico whiptail lizard reproduces parthenogenetically; the species has only females, and they are all virgins. Nonetheless, even though their eggs are not fertilized, females still have go through the motions of mating, with another female, in order to produce eggs. (Incidentally, this unusual mating system seems to be a result of the hybridization between two other lizard species.)

And even in species that have both males and females, homosexual behavior occurs in a wide range of species. Among Laysan albatrosses in Hawaii, for example, there appears to be a shortage of adult males. Raising a baby albatross takes a huge amount of work. Mom and dad have to take turns flying far away to get fish to feed baby, while the other parent stays with the nest. A single parent just can’t manage. As a result, many females pair with other females. They mate with males who are paired with other females, but nest and raise chicks together with their female life partner.

Rossellini says her Green Porno doesn’t have a political agenda. It is more about educating people about what the world is like for other species. But her videos do an excellent job of illustrating that in nature, sex involves an enormous range of diversity, from the exploding kamikaze penises of honeybees to the playful, anything goes sex of dolphins.

And learning more about the sex lives of other animals is useful for getting a broader perspective for the behavior of our own species, whatever we might personally find to be disgusting. Or not.