by Rob Dunn
Bollinger and Parker needed to wait for colons in order to confirm Bollinger’s instinct that biofilms were dense in the appendix. When the colons arrived, this is in fact what they showed, a kind of miniature forest of cells—a nest, you might even call it—of life. Bollinger’s interpretation is that the appendix houses large numbers of bacteria in biofilms that in turn offer services to our gut, for our benefit. In addition, Bollinger argues that the appendix is a shelter from the storm. When a severe pathogen such as cholera wipes out the good bacteria of the intestine, they can, from the appendix, be restored.
For now, what Bollinger, Parker, and colleagues have offered is the only hypothesis that makes sense given what we know about the appendix. The hypothesis explains other patterns that were associated with the appendix but poorly understood. It explains why appendicitis is common in developed but not developing countries, where humans more often get very sick, particularly from intestinal parasites. Such a pattern is what would be expected were the appendix, in developing countries, still performing its role of replenishing the gut. In contrast, the appendix in developed countries is infrequently challenged by pathogens. It may be understimulated (much as the immune system is more generally in the absence of parasites and/or pathogens) such that appendicitis is, in its way, like many other modern diseases, the consequence of the loss of species from our daily lives. When our appendices burst, it is because our bodies are turning on themselves. As for Dean Rector, the first patient of an underwater appendectomy, although he lived, tragedy would still find him. Later in the same year, Dean Rector died when a torpedo that his submarine had fired malfunctioned and did a U-turn. Like his appendix, it came back at him. This time, he had no chance to get out of the way.
It was a breakthrough to realize that our immune system, appendix included, might be helping rather than hindering the microbes in our guts. It reversed the false conclusions of decades of research in giant guinea pig chambers and suggested not only that we might benefit from our microbes but that over evolutionary time we had benefited so much that it was worth evolving specific antibodies and organs to make sure those microbes were treated well. Alongside this change of perspective ushered in by the work of Amy Croswell, Bill Parker, Randal Bollinger, and others, a whole new field of inquiry has emerged. For most of the history of human medicine, we have thought of other species as negative.10 Bacteria kill us. Fungi kill us. Worms, viruses, protists, and the other legions of biological doom kill us. What had prevented medical biologists before Parker (and others who were at the same time coming to similar opinions) from seeing what he saw was, in part, this vision of other species as deadly. At best, other species were seen as having no effect on us. But they could not be helping us. Mutualisms were reserved for the ecologists studying obscure organisms (tropical ants and termites, for example) in faraway lands.
The story of the gut, the appendix, and their bacteria is the tip of the iceberg, and we are only just beginning to see what remains hidden beneath the surface. Our bodies have adapted to interact with many species other than bacteria. You and I are like the colonies of leaf-cutter ants, dependent on other species without which we would not be entirely whole. We imagine ourselves besieged by germs, but this is a mistake. Our bodies are integrated with the microbes. In cross sections of our guts, it is impossible to say where the bacteria end and our guts begin. The IgA antibodies fail to recognize our good bacteria as foreign. Those good bacteria are, to IgA, self, the same as any of our other cells. While this new view of our lives is foreign to the medical community, to ecologists it is familiar. It is more the average way of living than the aberrant one.
It is hard to visualize the interactions of our bodies with other species, and for the immediate future it seems likely to remain so. We can imagine our guts and even the diminutive house that many of us are, right now, providing to bacteria in the form of an appendix, but even this is vague. Re-creations of the nests of leaf-cutter ants, on the other hand, offer a side window into what we might see. Recently, scientists unearthed an entire colony of a species of leaf-cutter ant. They poured gallon after gallon and then truck after truck of cement into the nest. The cement, mixed wetter than normal, poured down every tunnel into the great city of ants, killing first the workers, then the brood, and finally the queen, but in the process freezing for perpetuity a negative version of the construction. Other ant nests have been cast in this and similar ways, but none this big, none even close.
After several days of pouring, the cement finally filled the nest. It was allowed to harden and then, resembling nothing more than ants, the men began to excavate the soil around the now solid cast. As the cast was slowly revealed, its tunnels and chambers began to emerge. The scene looked like an archaeological dig. It looked like the Chinese excavations of the terra-cotta warriors, their heads, and then their shoulders and then their entire bodies emerging from beneath the sand. The workers kept digging. More tunnels. More chambers. And on the fifth day, the nest was revealed. The hole was ten feet deep and twenty feet wide. The nest’s form was that of a heart. The beating center, once filled with ants, was now stilled, and around the center were the arteries and veins and chambers of life. With patience one could see details: the garbage rooms, the dangling vaults of fungus, the queen’s deep quarters. It was all there. The cast had worked nearly perfectly. It was a work of art, the product of both ant and man, though mostly ant. Other smaller casts of ant nests have hung in museums. This one was too big, far too big. The men sat around it, though, as if in a gallery, stepping back to gain perspective, and then coming closer for detail. In that moment, they had something ever harder to get in science, perspective.
The physical nest of the ants has been sculpted by evolution to benefit not only the ants but also their partners. Special tunnels have arisen to ventilate the fungus. Chambers have come to be shaped so as to facilitate the fungi’s growth. Garbage chambers or piles are placed distant from the fungus, so that any pathogens that spring up on the dead might be isolated and controlled. Our body is not unlike an ant nest, composed of multiple cells and multiple species. What is surprising, though, is that while we are surprised but not shocked by the complexity of the relationships between ants and microbes, we don’t expect the same of our own bodies. We have no trouble believing that an ant colony depends on the complex microbial slew growing on individual ant bodies, in their guts, or covering and including their fungus. We have no trouble believing that subtle changes in the plant communities around ant nests are enough to fundamentally alter a colony. That the same is true of our own lives is somehow harder to believe. We think of ourselves as complex animals, sophisticated even, but somehow we imagine that a complexity of interactions is reserved for other species.
The appendix is a window into our similarity to the ants and other life-forms. Open the appendix and examine its contents. Spread them around. They are messy but they can be read. Their message seems to be that we have evolved, unique from our closest relatives, a special appendage to house bacteria, filled with IgA antibodies that help them to hold on. The appendix and IgA antibodies are a metaphor for our bodies more generally, bodies that fight some species, but also, whether we are conscious of it or not, have evolved special abilities to help others, some of them as small as a bacterium, others, it turns out, as large as a cow.
Part IV
How We Tried to Tame Cows (and Crops) but Instead They Tamed Us, and Why It Made Some of Us Fat
7
When Cows and Grass Domesticated Humans
Out with the bad, in with the good. We tend to think that the changes we have made to nature have disfavored species that harm us and favored those that benefit us. One might hope so anyway, but it is not the case, at least not universally, maybe not even on average. The species our brains urge us to disfavor are sometimes species that kill us, as with the nastiest of our worms and many of our microbes. But the species we disfavor also include most of the fruits and nuts we once harvested. These were the sweet a
nd fatty species that sustained our evolution, species that would have touched Ardi’s rough lips, species once treasured, but now ignored.
For much of our primate history, we spent hours a week picking and savoring wild fruits. The fruits benefited us. We also benefited their seeds by “depositing them” wherever we relieved ourselves. Some plant species spread around the world in this way, using latrines as stepping-stones. In this regard our ancestors were like toucans, emus, monkeys, and the many other species that serve plants as seed dispersers. We ate other things, of course. We searched out some insects—the queens of ants, for example, or the grubs of large beetles—but, for most of our story, the plants were the mainstay of our vessel. Today when we look out at our evolutionary partners, the ones not in our bodies, we see a very different scene. No less than half of all wild forests and grasslands have been replaced by agricultural and other intensively managed land uses. On these managed lands, we nurture a tiny minority of Earth’s species, our domesticates, whether corn, rice, wheat, or, more rarely, something else. These species are still our mutualists, but in a very different way from the papaya tree growing like a phoenix out of the outhouse. In making the transition from gathering thousands of species to farming far fewer, we caused both our favored species (domesticates) and our disfavored species to evolve, but they were not the only ones. We evolved too. The story of just how we changed begins with the earliest days of farming and what, from that seed, would ensue.
From a distance, farmed land seems possessed of both power and beauty. In early landscape paintings, fields glowed, pregnant with seed. But farming is a dark art. Bad years and hard days outnumber the good or easy, and yet we have to persist, regardless, because there is no longer an alternative. Once, we could find all the food we needed by simply walking around, searching. A hundred thousand years ago, all humans lived in Africa. Then, one lineage of humans (one branch on the human tree) left East Africa and made it to Europe and then later down to tropical Asia, Australia, and eventually North America. In all of that time, no one farmed. Everyone learned the species around them and collected and killed them. Then, over the last 10,000 years things began to change. Agriculture arose, multiple times in separate regions, and spread as it has continued to do ever since. Nearly all of the food consumed by humans is now farmed, whether in a field, pasture, or cage.
It is easy to forget how recently the world was otherwise. In the Amazon, for example, just 6,000 years ago, groups of humans were once small in number and lived along beaches, beside rivers, and under the canopies of trees. They gathered what they needed. Such groups would have stretched from Bolivia to Ecuador, spaced out and separate. These early settlements in the Amazon have been poorly studied. Bones and fossils are quickly broken down by roots and reinvigorated into leaves, termites, and beetles. Yet because the Amazon was colonized more recently than most of the tropical world, it provides as clear a portrait as we have of the transition from who we were to who we are. What we know is that once the Amazon was colonized, groups moved along rivers. They moved to the best spots and then, when the best spots were taken, beyond them. Year by year, more groups emerged, each with more individuals. The Amazon is immense, but finite. Wars kept some check on populations, as did lean years and infanticide. But eventually the Amazon abounded with humans running along under the trees. In each village, both in the Amazon and everywhere else on Earth, people would have learned the plants and animals around them, not all of them, but many of them. It was, in some real ways, a golden age of knowledge. Contemporary indigenous peoples living in tropical forests tend to know hundreds of plant species and perhaps a similar number of animal species, a large proportion of which are used, whether for foods, medicines, construction, or even as toys.1 If the same was true of their (and our) ancestors, hundreds of thousands of species might have been known and used globally. Collectively, our gathering forebearers knew the uses of more species then than we do now. They did not know about the germ theory of disease or particle physics, but they could distinguish the tasty fruits from the deadly ones and knew enough about the biology of each edible animal to know how, when, and where to chase it down.
Yet even though the indigenous peoples of the Amazon and elsewhere could extract nutrition from many different species, the growth of the forest and its creatures was not limitless. At least in some tellings, the Amazon, like the Congo or the forests of Asia, was a kind of petri dish, bounded by the Andes on one side and by oceans and deserts on the others. In this flat dish, populations grew more and more dense until there were millions of people in the forests, all of them gathering fruits, and killing monkeys and birds.2 Think for yourself about the possibilities in such a scenario. Populations would have grown until resources were depleted. And then what?
When human populations grew in the Amazon and elsewhere, they might have simply met with increasing rates of death and war. This is what happens to bacteria. It is the reason that we are not feet deep in great piles of microbes. Or they may have spilled over into marginal lands, farther from necessary water or easily accessed food. These were possibilities undoubtedly encountered in some places. The other possibility, though, was that some populations might find other ways of surviving. In such circumstances, two “inventions” repeatedly appear in history: agriculture and civilization—bread and kings.
As you think about your own life, it is worth wondering what effect the transition to agriculture had on you. It is worth wondering what kind of success came of being the ones who survived, no longer by the many fruits, nuts, and animals but instead by the few that would grow despite being harvested, the ones that might be tamed and that you now either grow in your garden or buy processed at the store. What happened, in other words, when history took the wild species of our original diets away? The answer depends as much on who your ancestors were and how their diets changed as on the simple fact that diets did change, more slowly in some places than others, but nearly everywhere eventually.
Let’s return to the Amazon. Across much of what we now tend to think of as the “pristine” Amazon, civilizations and agriculture once flourished.3 They flourished at the margins of the forest in seasonal lands where good years are good, but bad years are very, very bad. In those places, populations grew denser than elsewhere. Villages became great cities of thousands and then perhaps hundreds of thousands of individuals. One can fly over the Bolivian Amazon today and see the ruins of these civilizations, hundreds of miles of earthen, raised roads, the grid-iron prints of raised fields and everywhere among them, house mounds—the crumbling ant hills of man. Separate and similar civilizations arose in Colombia, Peru, and Brazil in concert with the development of agriculture. Peanuts, manioc, and sweet potato were farmed on long raised fields, separated by floodwaters. Other crops would grow at high elevations, where the Incas seeded their empire. But all across the region they grew, and as they did, people stopped moving their houses. Lifestyles changed. Humans went from who we were to something more like who we are, settled, agricultural, and dense.
Similar transitions would happen elsewhere in the world. We invented agriculture multiple times much the way a single storm might light many fires. It is typical to see this transition from hunter-gatherer to agriculturalist as one of our greatest human successes, the raging light of bounty. With agriculture would come complex societies and their trappings, writing, art, music, and the sort of unimaginable intricacy of culture we now confront in our daily lives. In many cultures, agriculture is afforded the special status of a blessing or rebirth. In some Amazonian groups, the first people are said to have come from a cassava plant whose roots, buried just right, sprouted legs, arms, and soul. Demeter, the Greek goddess of crops, brought springtime and youth. She and agriculture were, in no uncertain terms, the signs of our reemergence as a species that could change the land in such a way as to make it more bountiful. Though many insects have evolved the ability to farm, among the mammals we are unique. We learned to farm after the farming ants, beetles, and termi
tes, and so now, like them, we sow the fruits whose consequences we reap.
It would be easy to imagine agriculture to be at the root of our health and happiness. It is not. For one, with the transition to an agricultural lifestyle (from a dependence on many species to dependence on a few), life expectancies tended to decrease rather than increase. Hunter-gatherers seem to have lived longer, on average, than did early agriculturalists. In addition, various measures of “wellness,” the kinds that can be discerned from bones anyway, also worsened. The transition from hunter-gatherer to farmer tended to lead to an increase in disease burden, including digestive disorders associated with this new diet. Worse yet, the new agricultural diets were coupled with social hierarchies and haves and have-nots, so that even when there was enough food, not everyone received it. More than ever, with agriculture, survival came to depend more on status, culture, and the complexities that emerge from thousands or even millions of people living together than on avoiding predators or simply foraging for enough food.
One begins to wonder why, if agriculture had so many negative effects, we chose to engage in it in the first place. Farming is hard and unhealthy. So why do it? The answer, at least in part, may be that in many of those key moments in history when our ancestors chose to farm, the choice was not between the good days of hunter-gatherer society and agriculture, but instead between the worst days of hunting and gathering (when the food had run out) and agriculture. At least this is what Leigh Binford, an anthropologist at the University of Connecticut, proposed in the 1970s. Binford imagined that each of the many upwellings of agriculture came about when communities found themselves without alternatives—out of food and options. He said this not as a crackpot outsider, but instead as one of the most well-regarded thinkers in anthropology, which does not mean that he was always right or that other anthropologists have always agreed with him. Yet if he was right, it might mean important things for who we are. If each agricultural people started not from a great empire but instead from a few who struggled and made it, then each group of agriculturalists might have unique genes, genes of happenstance or even, just maybe, genes that allowed them to survive on their particular new crop or animal. Many of us might then descend from these small groups of individuals, the lucky few with their particular crops and genetic variants, the mutants who made it through.
