A great deal of my daily angst results from leafy spurge, a Eurasian plant most readers have never heard of. I mean this. A single, simple plant tears at my guts. During the growing season, I plot almost daily the next phase of my ten-year war with this species. Most people would call it a weed, yet this is not some simple garden pest; it infests uncultivated, native grassland communities. Biologists call it an “aggressive exotic,” a term that fails to communicate to those who are not biologists the seriousness of its threat. Yet when science considers these matters, aggressive exotics generally rank in the top five on experts’ lists of threats to habitat. Entire ecosystems are being lost to these plants, a loss that fails to register in the public consciousness, in part because we cannot imagine life swamping life, green killing green.
Leafy spurge made it into the United States during the nineteenth century, during a wave of plant importation from Eurasia. It has been in my region of Montana for about a hundred years, a brief tenure on the landscape, but it has nonetheless achieved a sort of critical mass. Enjoying the principal advantage of exotics—the absence of natural enemies—it multiplies unchecked, gradually supplanting all other plants, including healthy native grasslands. About one-fourth of my seventy acres is at least moderately infested. Using a variety of weapons, including some fairly sophisticated herbicides and an introduced insect that eats the plant’s roots, I have been able to fight it to a stalemate, but lately some colonies have shown signs of herbicide resistance, a prospect that chills me. Evolution happens. If
that resistance multiplies, the grassland ecosystems I value as habitat for elk and deer will be defenseless.
I’ve spent a lot of time looking at spurge close-up. Beyond its lack of enemies, the plant has evolved some sophisticated tools for defeating me, even before the herbicide resistance. It relies on rhizomes, fifteen- and twenty-foot-long horizontal roots just under the ground’s surface that support a plant twelve to eighteen inches tall. I can pull the plant off a mountainside, but I can’t get at the roots in land too steep, rocky, and wild for any sort of machinery. So much energy is stored in that root that it quickly fronts another stem. Worse, when I break a stem, the injury causes the plant to secrete a hormone that promotes growth. Five new stems appear where the previous one broke. These two relatively simple tactics, combined with its unpalatability to most grazers, are allowing spurge to win a war for the land—not just mine, but on rangeland from Nebraska and the Dakotas south through the plains and west through the Rockies.
If a single plant using a few simple tools can overcome modern methods to defeat it, how powerful, then, is a coevolved coalition of exotics?
We have asked why agriculture arose in the first place, but we must also ask why this isolated experiment spread across the planet to the lands of nonagricultural peoples who could see it coming and who, having had plenty of contact with agricultural societies, ought to have known enough to avoid it like the plague it was.
Perhaps this question is best considered against the immense backdrop of the Great Wall of China. According to long-held theory, the Chinese nation conscripted so much forced and slave labor into building the Great Wall in order to protect itself from barbarian hordes—nomads—to the west. To be sure, the Mongols were a problem throughout Chinese history. But some scholars have advanced a different theory: that the wall was built not so much to keep the Mongols out as to keep Chinese peasants in. Certainly anyone who got a good look at equestrian life on the steppe would prefer it to stoop labor in the rice paddies of that intensely hierarchical society.
Agriculture’s just-so story, however, says the motion should have
been in the opposite direction, that it was contact with farmers that spread the joys of the plow among the heathen. The assumption is that nomads and hunter-gatherers, who usually traded with civilized folk, knew a good thing when they saw it and so simply adopted the farming technology. In other words, a bunch of guys who spent their time running around the woods, hunting and fishing and trading meat for sex, one day saw someone hoeing weeds and said to themselves, “What a fine idea! Let’s go do that instead,” Is it possible that the technology did not spread entirely by adoption, that hunter-gatherers were wiped out or displaced by an advancing agricultural imperialism? The record suggests that although some adoption did occur, by and large farming spread by genocide. Those hunter-gatherers who apparently chose to adopt it tended to pick and choose, to assimilate only those parts of it that were attractive to them—pastoralism most often. It is easy to understand how a shift to pastoralism, herding domestic animals, was a relatively small and natural step for hunter-gatherers, who already followed wild herds across their native ranges. As game became scarce, some hunter-gatherers got closer and closer to wild herds and then began to integrate them into their wanderings, so that some of the wild goats, sheep, and cattle became domestic. Their association with the animals amounted to selection pressure that fostered domestication, but the domestication of wandering herds was not a transitional step to agriculture, to growing crops. Domestication of crops came first, an order that holds up in all of the major agricultural centers. Row-crop farmers, not hunter-gatherers, were the first to domesticate livestock. Pastoralism as a separate activity later spread from the agriculturalists to the nomads, a case of selective adoption of an agricultural trick. Choosing what worked in their milieu, especially in arid grasslands, nomads reached for the shepherd’s crook but ignored the plow. By and large, though, when agriculture spread as a full-blown system of technologies—plows, wheat, cattle, cities, and priests—it did not diffuse among people but displaced them, and “displaced” is a euphemism.
To some degree, all of the major systems of agriculture did spread. By the time of the Spanish conquest, maize had made its way from its site of domestication north to the upper Mississippi and Missouri
basins and south to the Andes. That long north-south axis, however, placed some pretty severe constraints on the spread of the full complement of domesticates in the New World. Not all of Mexico’s crops could travel across the tropics and the equator to Peru and vice versa. But some, such as maize, could.
The rice culture of Asia did its share of moving as well, largely south into Southeast Asia, but also west as far as North Africa. Rice was in the Middle East three thousand years ago. Nonetheless, rice farming is a lowland activity that works best in major river valleys and estuaries of the tropics. There were constraints with rice, but not nearly so many with the special coalition of crops and animals developed in the Middle East: wheat, barley, goats, sheep, and cattle were all far more portable. In addition, their domestication occurred at the very southern edge of a vast, fertile plain that stretched from the edge of Siberia, across what is now Russia, west through northern Europe and to the Atlantic. This, of course, is an east-west axis spanning a broad stretch of a temperate zone, with similar conditions every bit of the way. The coalition led by wheat and cattle didn’t have barriers to jump, at least not in Eurasia; it found fertile ground all the way, the argument at the center of Jared Diamond’s Guns, Germs, and Steel and in Alfred W. Crosby’s earlier book, Ecological Imperialism: The Biological Expansion of Europe, 900–1900.
This culture began by spreading from what is now southern Turkey and northern Iraq north to the area between the Black and Caspian seas, near the Caucasus Mountains. It refined its techniques here, and formed its own language group, Indo-European, the mother tongue that would found Sanskrit in India and English at the opposite edge of the axis. Another name for the wheat-beef culture is “Caucasian.”
Much of this early spread encountered no resistance. It colonized lands that were vacant or only sparsely settled by hunter-gatherers, who moved on. This was true, for instance, in Greece and Italy, which lacked the sort of hunting conditions and megafauna that would have supported large groups of hunters. Here, diffusion was simply a matter of agriculture’s increased birthrate sending colonists into unoccupied lands. About the same time, there is evidence of
some pastoralism spreading among hunter-gatherers, specifically the Cro-Magnon people near the Mediterranean. To the degree that this happened, it was a big change for the people who had occupied that region for at least thirty thousand years before the farmers moved in. These Cro-Magnons are the people responsible for the famous cave art of France, and their art itself tells us they probably had very little incentive to change during all those years. Ian Tattersall, curator of the department of anthropology at the American Museum of Natural History, summarizes their existence in Becoming Human:
The late Ice Age inhabitants of southern France and northern Spain lived in an area greatly favored by geography. This relatively sheltered limestone region boasted a huge range of habitats, from hilly crags, where ibex abounded, right down to the valley floors, where rivers teamed seasonally with migrating salmon. Perhaps never before had fully modern humans ever lived in such a productive and varied environment; and if so, the visual stimuli to artistic production had never been so great.
This relatively peaceful spread of agriculture accelerated and became more aggressive at the opposite edge of Europe, in what is now Hungary, about seven thousand years ago. The original Caucasian farmers adapted very quickly to the rich loess soils of the Hungarian plain (which are similar to Iowa’s rich loess soils), and there fine-tooled a system based in beef and wheat. These people had a taste for the virgin soils of a frontier occupied by hunting and gathering natives, and conquest here would be swift and violent, a foreshadowing of the developments in the American Midwest in the nineteenth century.
The archaeological term for these neolithic cowboys is Linearbandkeramik, derived from the German word for their distinctive pottery and commonly abbreviated as LBK. They were Europe’s original wheat farmers, bringing themselves and their bit of food-storage technology in from what is now southern Turkey. The most revealing marker of their culture’s spread was this pottery’s sudden
ubiquity across Europe. Sites dated from a relatively brief period of 6,700 years ago to 5,900 years ago occur throughout the northern European loess plain, from France to the Ukraine and south into the Danube basin. The anthropologists T. Douglas Price, Anne Birgitte Gebauer, and Lawrence H. Keeley write, “Perhaps the most striking feature of LBK is its remarkable homogeneity in material culture, settlement pattern, and economy over this huge region … . Such remarkable homogeneity must evidence either a very rapid spread or a pathological conventionality or both.”
It was as if future archaeologists were to find dumps from Des Moines full of Tupperware.
The same group of anthropologists concluded that this culture’s sweep through Europe took no more than three hundred years, a blitzkrieg by the standards of the day. And it is appropriate to employ the war metaphor here, in that the record suggests, contrary to conventional ideas about rational and peaceful cultural diffusion, that there was almost no intermixing among the wheat farmers and the salmon-eating, cave-painting Cro-Magnon already resident.
The curious part of this is that there was probably not an inherent ecological reason for conflict. That is, the LBK people didn’t blanket the region, at least not at first, but tended to cluster in villages where loess soils were concentrated, leaving the river-valley bottoms and mountains untouched. That would have left a viable niche for hunter-gatherers. A coexistence with mutually beneficial trade could have developed between the two cultures, but the record says it didn’t. There is almost no record of Cro-Magnon artifacts in LBK villages and vice versa. Cro-Magnon sites seem to cease being occupied at about the time of LBK arrival. In fact, the record seems to show that the Cro-Magnons maintained a sort of buffer zone between themselves and the newcomers, leaving even in advance of the advancing farmers.
The exception to the absence of artifacts from one culture in settlements of the other is evidence that the two sides swapped spear points, probably not as trade goods. “All these artifacts are weapons,” note Price, Gebauer, and Keeley, “and there is no reason to believe that they were exchanged in a nonviolent manner … . The evidence
from the western extension of the LBK leaves little room for any other conclusion but that the LBK-Mesolithic interactions were at best chilly and at worst hostile.”
Can we then conclude that the farmers killed all the Cro-Magnons? There are a couple of ways to pursue this question. The record of human migrations is well-preserved in genes and in languages, both of which evolve along similar principles. The Italian scientist Luigi Luca Cavalli-Sforza, now a professor of genetics at Stanford University, has spent a lifetime chasing these questions across the disciplines of archaeology, anthropology, genetics, molecular biology, and linguistics. He leans heavily on the latter three when he summarizes his findings in his 1995 book The Great Human Diasporas. The genetic record matches the archaeological one, he found, and is consistent with the notion that the farming culture originated in the Middle East, from which it spread very quickly across Europe. These people’s genes dominate in modern Europe. There was some genetic mixing, but this does not mean the spread was amicable. The spread of these same farmers, my ancestors, in North America was genocidal and violent, yet my seemingly Caucasian body carries the genes of my Chippewa Indian ancestors. Conquering people take brides, slaves, and concubines from the conquered.
The intriguing part of Cavalli-Sforza’s genetic analysis, though, shows a small island of genetic resistance, a surviving pocket of what he believes are Cro-Magnon genes, in southern France and northern Spain, the area now or recently occupied by Basque-speaking people. The record says those same people once occupied the broader area of southern France that holds the famous cave paintings. The linguistic case is even more interesting. Almost all of Europe speaks a derivative of the Indo-European language that began near the Caucasus Mountains and hybridized later in the wake of both Greek and Roman expansions. There are, broadly speaking, only two exceptions. One is the Uralic languages: Finnish, Estonian, and Hungarian. The other is Basque, a linguistic island. Linguists have dug deeply for languages related to Basque. The closest they have found are ancient tongues, including Na-Dene, spoken by some North American natives, and another spoken by some Sino-Tibetan peoples. Writes
Cavalli-Sforza, “Basque descends from the language spoken by the first modern humans to come to Europe, the Cro-Magnon.” It may be that the plight of modern Basques—their long, bitter struggle with the ethnic majorities in Spain—stretches back to spear points in LBK camps.
About 5,500 years ago, houses in southern Scandinavia got bigger. Storage areas were attached to individual, not communal, homes. Burials became more elaborate. One would expect to find wheat and barley on the scene, and they are. Agriculture arrived, but not in the same manner as it had on the plains to the south. In the areas that are now Denmark and southern Sweden, it appears that the existing people were not overwhelmed and conquered by advancing farmers, but slowly adopted agriculture over the course of about a thousand years, as opposed to three hundred in the much vaster European plain.
What was different? Probably the answer is sedentism. The people in Scandinavia already lived a settled life before farming came. They were among those people throughout the earth who had gathered at the edge of productive rivers, estuaries, and seas. The archaeological record indicates they lived rather abundantly on fish, mollusks, and marine mammals. In fact, their settlements looked a lot like those that had given rise to agriculture much earlier in the Middle East. Their stable economy seems to have given them some firm basis on which to resist the onslaught of the farmers. In addition, they lived at the edge of what was at the time a dense forest, becoming denser as sea levels rose with the decline of glaciation. This was not the open loess plain that allowed agriculture to spread unchecked. In Scandinavia, the wheat-beef complex met its northern ecological limits. It did slowly take root in this land, but only as the people who already lived there and knew best how to survive there retooled it to fit their needs.
There is clear evidence of trade in this region at the beginning of this period. Artifacts made by and imported from the farmers to the south, including polished stone axes, amber, copper jewelry, and copper axes, appear in Scandinavian settlements. This suggests that
there was plenty of contact between the two groups, enough to allow traders to occasionally borrow technology and domesticated animals. At the same time, there is evidence that food from the sea was becoming scarcer, so the Scandinavians would need some of the food agriculture could provide. That’s not to say all of this happened in peace and harmony. Cemeteries are full of murder victims, both before and after farming came, and the period was likely as violent as any other. But while there is evidence of cannibalism among both groups, the northern transition to agriculture was not prosecuted by conquest and genocide. The violence was retail, not wholesale.
The European expansion of farming thus provides two models for looking at what would come after. The parallel records in the United States lie in the remaining Indian reservations on the vast plains near my home in Montana. They are poverty-wracked, long-term concentration camps for hunter-gatherers whose bison, elk, and deer were largely wiped out by advancing wheat farmers. By contrast, the natives along the northern Pacific Coast of British Columbia and Alaska, remnants of a salmon culture that historically derived some 95 percent of its nutrients from the sea, live on in a traditional life that is relatively intact. These are not concentration camps but communities with a viable economy. Art forms that developed before white settlement persist, as does a reliance on salmon fishing. The thick coastal forests of the Cascades won’t grow wheat. In places like Prince Rupert, British Columbia, both natives and whites still do what people have done there for five thousand years: they fish. A city council member is as likely to be Tshimshian as Swede. (Many of the immigrant communities here are Scandinavian.)
In fact, the similarities to Scandinavia’s transition to agriculture are strong enough to suggest that they mark not a parallel but an extension of the same expansion. After all, the conquerors of North America are descendants of the very same people who swept the Cro-Magnons out of Europe.
“Perhaps European humans have triumphed because of their superiority in arms, organization, and fanaticism, but what in heaven’s
name is the reason that the sun never sets on the empire of the dandelion?” This is one of the fundamental questions asked by Alfred W. Crosby in Ecological Imperialism. Crosby traces the extension of the expansion that began five thousand years before in Europe proper to create what he calls the “neo-Europes”: the temperate regions of North and South America, New Zealand, and Australia. (Some would include South Africa as a neo-Europe as well.) The core of the neo-Europes is made up today of New Zealand and Australia plus the United States, Canada, Argentina, southern Brazil, and Uruguay. These are the nations now dominated, if not demographically, certainly economically and politically, by Caucasians, as demonstrated most obviously by the prevalence in these places of European surnames. Less obvious is an even more important marker of dominance. In 1998, the seven countries on the list accounted for about two-thirds of all wheat exports in the world, and about 70 percent of all maize. These are the most important two of the big three grain crops that account for two-thirds of the world’s nutrition. That is to say, the new Europes drive the world’s agriculture. The dominance does not stop with grain. These seven countries, plus the mother ship—Europe—accounted for three-fourths of all agricultural exports of all crops in the world in 1999.
The single outsider that can claim some standing in this group is China, which is becoming a major player, not in exports of wheat and maize but, more important, in their production. Although it is not a neo-Europe, China feeds itself not just with rice but as the world’s leading producer of wheat and a significant grower of maize. China has vast stretches of temperate lands at the same latitude as Europe’s wheatfields. Its strong, long history of rice agriculture allowed it to successfully resist European invasion, but it has taken advantage of its ecology and long-standing trade with the West to prosper with European crops.
I lay all of this out to justify what may appear to be a Western bias, or Eurocentrism, in my narrative. Certainly there is more to agriculture, and to culture itself, than what arose in Caucasian Europe. The modern story of imperialism and conquest, however, is decidedly European. We can track that dominance through the spread
of wheat and corn, but it is just as valid to do so by following the spread of the English and Spanish languages, of wheat-, milk-, and sugar-tolerant digestive systems, of smallpox-tolerant immune systems, of horses, leafy spurge, beefsteak, or, as Crosby does, dandelions:
By 3,000 years ago, give or take a millennium or so, “superman,” the human of the Old World civilization, had appeared on earth. He was not a figure with bulging muscles, nor necessarily with bulging forehead. He knew how to raise surpluses of food and fiber; he knew how to tame and exploit several species of animals; he knew how to use the wheel to spin out thread or make a pot or move cumbersome weights; his fields were plagued with thistles and his granaries with rodents; he had sinuses that throbbed in wet weather, a recurring problem with dysentery, an enervating burden of worms, and impressive assortment of genetic and acquired adaptations to diseases anciently endemic to Old World civilizations, and an immune system of such experience and sophistication as to make him a template for all humans who would be tempted or obliged to follow the path he pioneered some 8,000 to 10,000 years ago.
Farmers in this period may not have lived by “bulging forehead” alone, as Crosby indicates, a characterization that challenges the technology-centered explanations for agriculture’s spread that have dominated our thinking. Still, technology played an enormous role, as did the east-west axis of agriculture emphasized by others. By two thousand years ago, agriculture had become a continuously linked band stretching all the way from Spain and the British Isles in the West, through China, Japan, and Indonesia in the East, including all of the Indian peninsula. This trade region included a narrow band of North Africa along the southern Mediterranean that was thoroughly integrated into the whole. Imperial Rome, for instance, got most of its grain from Egypt. No longer, then, was there a distinct European agriculture. The main mass had become truly Eurasian, bordered by a band through what is now Ethiopia in eastern Africa and a sub-Saharan
strip of purely African farming. Separate still, but already thriving, were agricultural societies in the northern half of South America, all of Central America, and, in North America, smaller regions of the American Southwest and the corn culture of what is today the southeastern United States. Finally, there was a thriving agricultural center in the West African region known as Senegambia. The people there had independently domesticated a species of rice separate from Asian rice. All of this combined to support what became, by five hundred years ago, the world’s first half-billion people.
A good part of what powered this expansion was technological leaps, aided and abetted by widespread trade and contact across the main Eurasian band. The Chinese, for instance, had adopted Europe’s big invention—wheat—by three thousand years ago, but they also contributed greatly to the technology used by European farmers during the same period. Arguably the biggest technological leap of the era was the invention of the horse collar about 1,500 years ago in China. Before this, tillage in both Europe and Asia had depended heavily on oxen and a throat-and-girth yoke that suited those ponderous beasts. The same harness was used on horses, but was so inefficient that it greatly limited the load and mobility of these much faster animals. A smaller horse collar allowed a quantum leap in the load a horse could pull, so fields became larger and more widespread almost immediately. This invention traveled quickly from China to Europe.
Agricultural historian L. T. Evans writes:
The introduction of the padded horse collar also had profound effects on agriculture, by allowing the greater strength, endurance, and mobility of horses to be utilized. Cultivation became more timely. The farmers could live further from their fields and therefore in larger villages with more diverse opportunities, while the sale and faster transport of surplus produce encouraged commerce and the growth of cities.
In short, this simple innovation probably had as profound a role in reshaping the world of that time as internal combustion and tractors have had in our own.
It also made the two legs of European agriculture into a tripod. Wheat, cattle, and horses formed the trinity that, when carried by humans to distant fertile ground, would eventually colonize the world. These three, however, did not act alone. In fact, the broad region of Eurasian farming developed a coalition of domesticates and fellow travelers that would be every bit as important in this conquest as the three species that spearheaded it. Just as in the case of the horse collar, a key to this evolution was the broad east-west band that allowed technology and new or newly vitalized species to spread. The wide geographic band allowed for diffusion, evolution, and synergy. This was certainly true of technologies like cotton spinning (which began in India but quickly spread to the Middle East) but also of new crops and varieties of crops that developed to match slight climate variations.
While the Chinese were adopting rice, for instance, the people of the Indian subcontinent were taking what were to become their mainstream crops of sorghum and millet from Africa, cucumbers from the Himalayas, cannabis from Central Asia, and sugarcane, bananas, and taro from Southeast Asia. Humanity, even in prehistoric times, was already deeply involved in an African-Eurasian economy (if not a global economy). The trade that made this possible also allowed for a variety of freeloaders and stowaways to work their way through the system. The cultivation of storable food created an enormous new niche for whole classes of parasites, insects, birds, rodents, and vermin that fed on those growing fields and stored crops. The best example is the common rat, a European contribution that would become a strong ally of agriculture in subsequent conquest.
A new niche opened for a class of plants as well. Agriculture is based on those very few plants that thrive on disturbance and produce lots of seed. There is a wider group, however, that thrives under catastrophic conditions but without the payback of seed for humans, a class of plants commonly called weeds. Once catastrophic agriculture cleared the path for them, weed species once relegated to floodplains or the edges of forest fires could run in that same contiguous band as farming did, from Britain to Japan. Within that territory, they could evolve, develop, combine, and invent in tandem with humans
and human technology. Weeds, like humans, traveled, traded information (genes) with other weeds, and got better at what they do.
Crops, weeds, vermin, and pests developed into a coalition, a cast of characters that depended on one another and traveled together, led by the plow; however, by no means was the most formidable element of this phalanx its visible players.
Our consciousness of the devastation smallpox wrought has focused on the New World and the inherent susceptibility of Native Americans, but the disease is far from a New World problem alone. It also devastated some remote corners of Eurasia that agricultural society reached late in its period of expansion. Smallpox first appeared among the Ostyak, Tungus, Yakut, and Samoyed peoples of Siberia in about 1630, plenty late enough for us to have a clear record of its effects. Crosby writes that it swept “like a scythe through standing grain. The death rate in a single epidemic could soar past 50 percent. When it first struck Kamchatka in 1768—69, it killed two-thirds to three-fourths of the indigenes.”
The pattern repeats itself with a series of infectious diseases three centuries later. In 1943, the Alaska Highway pushed into parts of the north that had previously had no significant contact with Europeans. There followed a year-long epidemic of measles, German measles, dysentery, jaundice, whooping cough, mumps, tonsillitis, and meningitis, Crosby reports. A similar event among Eskimos and Indians spread throughout northern Quebec in 1952, killing 7 percent of the people, a relatively low death rate, probably thanks to modern medicine. Modern medicine, however, also gave us better diagnoses, and therefore a better catalogue of the maladies that played a major role in the conquest of the globe by the agricultural Europeans.
Scars on bones tell us that agricultural people themselves dealt with disease from the beginning of agriculture. So does the written record; epidemic diseases were probably at the root of the biblical plagues in Egypt. The first book of Samuel in the Old Testament speaks of a plague, probably bubonic plague. Throughout Eurasia, farming people dealt with epidemics of smallpox, influenza, malaria,
measles, chicken pox, and other devastating illnesses long enough to develop immunities. These immunities were a key factor in the domestication of humans. Infectious diseases were selection pressure, and a lot of farming Eurasians no doubt went the way of the aborigines in the neo-Europes. Those who survived, however, were shielded. So the just-so story of European expansion that depicts a rapid march through the primitive world thanks to a superior technology, an evolved and more efficient way of life—seen in North America as a “manifest destiny”—must not credit only technology-driven weaponry and religious zealotry; it must be revised to take into account also the preceding conquest wrought by disease. We are beginning to understand that by the time the conquistadors struck the Andes or Custer reached the Black Hills of South Dakota, only shadow populations of natives remained. The Indian wars got the headlines, but they were mopping-up operations. The shock troops were diseases, especially smallpox, aided by weeds and a few other members of catastrophic agriculture’s evolved coalition. Crosby and Diamond both make convincing cases that, at its roots, conquest was biological, not technical.
All of these diseases moved through these untouched territories according to the rules of what are called “virgin soil epidemics.” Under those rules, nearly every person who falls sick dies. Infection rates are death rates, partly helped by the fact that infection is so widespread. So many people are sick that few healthy people are left to attend to the sick and to help them survive. Crops go unattended; no one hunts; food sources dry up.
When whites arrived, the indigenous people of the New World had already established lengthy trading routes, and the vanguard of Europe spread along those routes in advance of the colonizers. Further, tribes and villages hit with smallpox or some other epidemic would often take the nomads’ solution to adversity and move, and this movement became yet another ally of the pathogens.
The vanguard of the United States’ conquest of its territory was the Lewis and Clark Expedition, which reached the mouth of the Columbia River in the winter of 1805—6. Lewis and Clark were there to detail what we now regard as initial conditions among the natives,
but Captain James Cook had been there almost thirty years before, the first white contact in the Pacific Northwest. He saw towns that were depopulated even then, and he specifically reported seeing natives bearing smallpox scars. Lewis and Clark spent their first winter on the high plains among the Mandan. The early chapters of their journals detail the tribe’s thriving existence. Smallpox later wiped out the Mandan.
The conquistador Hernando de Soto swept through what is now the southeastern United States between 1539 and 1542 to find what we can only describe as an advanced agricultural society, only slightly less developed than Aztec Mexico at about the same time, and with a similar foundation for its agriculture. Based on his reports, the population of Florida was estimated at the time to be nine hundred thousand. He found cities, trade, and royalty along the (later-named) Gulf Coast of Florida between Tampa Bay and Mobile Bay, along the Georgia Coast, along the Mississippi River, in eastern Mississippi, and in southern Arkansas and Louisiana. Then he left. When the French arrived in the same area in the eighteenth century, they found a few primitive villages. The fields of maize were gone, and bison, which de Soto had not seen, had moved back into the deserted landscape. De Soto left without conquering the region, but he left smallpox behind, and disease wiped the slate clean of natives to allow subsequent colonization.
Crosby records a sort of reverse example of the spread of smallpox that helps explain its virulence for natives, and in the process credits the disease with undermining the Anglican Church in America. Unlike other denominations, the Anglicans (fittingly) maintained a rule that would-be bishops must be trained in Britain. Thus, aspiring second- and third-generation colonists would make the trip back to the motherland. Smallpox, however, was not widespread in white settlements in the New World. Immunity to smallpox is not strictly hereditary but accrues in childhood, when children are better able to fend off its effects and when they tend to contract the less virulent forms that confer immunity to the more lethal forms. When the would-be bishops hit the streets of England as adults, they usually caught smallpox and died.
Dead clergy notwithstanding, at least some New World settlers considered smallpox a net gain for their god. John Winthrop, the first governor of Massachusetts Bay Colony, was blunt about the matter: “For the natives, they are neere all dead of small Poxe, so as the Lord hathe cleared our title to what we possess.”
If that long Eurasian east-west axis was such an advantage to the supercontinent, then, presumably, an even longer axis would increase the effects that much more. The larger axis is not simply a thought experiment, but existed periodically during glaciation, when sea levels dropped to make the Bering Strait a land mass, Beringia. On this planet, glaciation is not the exception but the norm. Over the last billion years or so, a regular cycle has governed the earth, characterized by glaciations lasting sixty to ninety thousand years, interrupted by brief interglacials of roughly ten thousand years. All of the history of human civilization has been compiled within the present interglacial, which, at the moment, is about out of time.
We know that the last glaciation brought humans to the New World. We have already seen the upheaval this brought for the large mammals native to the continent. During this same period, however, a second bit of commerce occurred that was to set up the expansion of agriculture in Eurasia and its spread in the New World more than ten thousand years later. Eurasia got horses from North America. Horses evolved in the New World as part of the rich complement of . fauna of the great interior grasslands. Paleontologists tell us that the development of flat grinding teeth in horse fossils about sixty million years ago signals the rise of the Rocky Mountains. That cordillera formed a “rain shadow” that dried the flat interior, making for arid grasslands. Grass is tough and requires flat, grinding teeth. So the Rockies “built” a creature ideal for colonizing the similar steppes of Central Asia, a development the kin of Genghis Khan would later celebrate.
Horses were among the doomed megafauna of the New World, hunted to extinction by the human immigrants moving across Beringia. The species, however, had already migrated to Eurasia during
one of the ice ages and eventually became the premier domesticate of Eurasia, greatly enhancing farming and transportation (on which agriculture’s cities came to depend) as well as warfare and conquest, equally vital institutions of agricultural society.
The power of the horse to reshape society was immediately manifest in the New World when they were repatriated there by Europeans. Like smallpox, the horses introduced by the Spanish conquistadors spread in advance of the whites themselves. This was especially true in the interior grasslands, where horses had evolved originally. So fitted are these animals to this environment that descendants of those introduced Spanish ponies still survive as feral herds in the Great Basin. The natives found them exceedingly useful for hunting, so much so that once they were introduced, long-settled corn-farming communities of the Mississippi valley gave up farming to hunt bison on horses. It is tempting to record this as a footnote of agricultural history suggesting that, given a choice, people would sooner hunt than hoe, but something else is probably at work here. As smallpox spread in these communities and among existing nomads, it probably became difficult to maintain the social organization that farming required, just as it became an advantage to be on the move. In addition, hunting methods before the horse required mass drives on foot, which also depended on a certain amount of social organization and structure. A lone, mounted hunter, however, could be effective in hunting bison, particularly after rifles arrived.
Interestingly, the experience in the North American plains runs counter to the spread of European agriculture in the rest of the temperate regions of the globe. The difference was bison. There were close relatives of and species of bison around the world, just as there were ancestors of bison in the fossil record in North America. The closest relative extant is the European steppe bison, now limited to a relict population in Poland. Thus, there is some cause to believe that the particular species that is the American bison evolved with human hunters in Eurasia and crossed the land bridge to replace the ancient species hunted to extinction by the first immigrants. If this is the case, then the American bison is, in the long view, an exotic. In any event, North America was unique. Humans hunted the big grazers to
extinction when they first arrived in North America, New Zealand, Australia, and South America, leaving an enormous, unfilled niche, but only in North America did the immigrants bring a replacement, the bison, to fill that void. The presence of bison allowed the North American nomadic hunters to maintain a strong economy based in bison and to resist white encroachment until the very end of the nineteenth century. This economy collapsed only after American colonizers developed a deliberate policy of exterminating the bison, reducing its numbers from about seventy million before white settlement to fewer than fifty in a half century, all in small private herds or in Yellowstone National Park.
Elsewhere, horses and other big grazers stepped into an empty niche and almost unlimited possibilities for expansion. In South America, the biggest native grazers were llamas and alpacas—camels really, but little and docile ones, hardly competition for horses. The Spaniards attempted to settle in what is now Argentina in the early 1500s, but failed. They did, however, leave behind some horses. When they returned to try colonization again in the 1580s, they found horses in abundance. A traveler at the turn of the seventeenth century reported horses “in such numbers that they cover the face of the earth and when they cross the road, it is necessary for travelers to wait and let them pass, for a whole day or more, so as not to let them carry the tame stock with them.” In 1744, a Jesuit in the pampas reported herds of feral horses so numerous that it would take three hours for them to pass by “at full speed.”
On North America’s East Coast (where bison were scarce), feral horses reached such numbers that they were a nuisance—but a convenient nuisance. Frontiersmen had cheap mounts for the taking, simply by capturing wild animals. Horse colonization followed a similar pattern in Australia’s great grasslands. By the mid-nineteenth century, wild horses had become so abundant as to be declared “a weed among animals.” Australians killed them for their hides, which fetched only about four shillings apiece. Once the hide market became glutted, the animals had almost no value and settlers knifed or otherwise wounded them so they would run off and die elsewhere.
At the same time, horses were enormously expensive in Europe,
their possession out of reach of the average farmer. Because horses were the very engine of the agrarian economy, their availability in the New World was key to the economic potential of the region. Crosby sums this effect: “Horses in such profusion, tame or feral, existed nowhere else on earth. Their abundance shaped the societies of the pampas more firmly and more permanently than the discovery of gold would have.”
The unoccupied niche for big grazers was as welcoming to two of catastrophic agriculture’s most crucial and long-standing allies, cattle and sheep. They spread as the horses did, in a profusion analogous to the virgin-soil epidemics that spread the key pathogens of the time.
Cattle did not immediately adapt to the tropics, where they were first introduced by Columbus in 1493, but they survived. Subsequent introductions by conquistadors in South and Central America and the southwestern United States in the sixteenth century, however, brought them to temperate grasslands more to their liking. They literally went wild, their populations doubling every fifteen years. So well were they adapted that they could propagate without human aid, so that when, for instance, Jesuits abandoned a mission on the pampas in 1638, the five thousand cattle left behind didn’t skip a beat. By 1700, there were an estimated forty-eight million feral cattle on the pampas, roughly equivalent to the number of bison on the Great Plains.
The animals did nearly as well in the eastern United States, with feral herds numbering in the thousands. Many were captured and slaughtered, rendering some settlers wealthy beyond the imagination of their European forebears. At the same time, though, the cattle were independent enough to proceed with settlement on their own, in advance of their human colleagues. They wiped out native grasslands, in many cases before whites ever saw them, paving the way for the European flora to follow. A horde of cattle hooves works like a plow.
Essentially the same story played out in Australia in the eighteenth and nineteenth centuries. By the end of the period, feral cattle would number in the millions in the interior grasslands. The only thing that prevented Australia from being overrun with cattle was
sheep, which became increasingly important in the subcontinent as well as in the rest of the neo-Europes as textile manufacture mechanized in the nineteenth century. This development made grasslands economically important enough to wrest from cattle and cattlemen.
While the grassland troops were the grazers, swine worked around the edges, preferring more tropical and wooded areas. Pigs found the living easy in Brazil, the West Indies, Central America, the southern United States, and Australia. Just a decade after their introduction in Hispaniola by Columbus, their prodigious reproductive capacities caused feral hogs to be listed as “infinitos.” They literally swarmed the hillsides, vacuuming them of vegetation.
From a human point of view, the mammals were the most significant introductions of the period, but moving with them was a tide of fauna and flora with probably as much significance for native species. From the beginning, explorers brought honeybees to the New World, the bees spreading in advance of human settlement just as the mammals did. Clearly, this paved the way for European crops and weeds, many of which are pollinated by honeybees. But these introductions had profound implications for native plants as well. Pollination is a finely wrought relationship, providing some of the most intricately entwined examples of coevolution. There are, for instance, trumpet-shaped flowers of a certain color that attracts a particular species of hummingbird, which, in turn, has a beak of exactly the correct shape and size to pollinate that specific flower. The New World obviously had its own pollinators and plants dependent on them, but as honeybees spread, they broke up some long-standing relationships, likely wiping out vulnerable species even before Europeans knew they existed. Some native species, like eucalyptus in Australia, did benefit from honeybees’ efforts, but even in such cases the ecological balance was altered, allowing certain native species to out-compete others.
One need not know very many plants to appreciate their impressive power to tell the history of a place. One can, for instance, travel to a trail-top summit in Montana’s Glacier National Park, one of the most
pristine and protected places in the United States, and find among the native flora the distinctive blue-tipped leaf and airy seed head of Kentucky bluegrass, the same plant settlers found growing in what would be Kentucky when they first crossed the Appalachian Mountains. But Kentucky bluegrass is not from Kentucky; it’s from Europe and was introduced on the East Coast when marauding cattle made a place for it. Like smallpox, bees, and cattle, it traveled ahead on its own. It grows on summits in Glacier Park because the area was used by horse packers, and they deliberately brought the seed and scattered it so that their horses might have something to eat.
The practice of seeding to promote conquest began with conquest itself. Long before Columbus made his discovery, Spain began practicing for colonization with the conquest of the Canary Islands, which were immediately “seeded” with sheep and swine. Throughout the period of exploration, mariners typically carried these animals aboard and dropped them on strategic islands along the way, along with handfuls of grasses and other plants they thought might take root and provide sustenance so that sailors would have a food supply when they returned years later.
The last of the neo-Europes to be settled was New Zealand, and by then colonizers had perfected their strategies for usurping native land. Not surprisingly, seeding was a prominent tactic. Crosby quotes a leader of a French expedition to New Zealand: “I planted stones and pips wherever I went—in the plains, in the glens, on the slopes, and even on the mountains; I also sowed everywhere a few of the different varieties of grain, and most of the officers did the same.” Comments Crosby: “It did not occur to any pakeha [white settler] for decades and decades that spilling and strewing alien organisms into an ecosystem can be like lighting a candle in order to lessen the gloom in a powder magazine.”
At the time, much of this seed was dirty—that is, full of weed seed. Thus, the practice of seeding provided a ride for the botanical equivalents of rats and smallpox. The long list of pre-Columbian domestications from the central Mexico Valley gives us some indication of the richness of its native flora; it was a center of biological diversity. Yet, today, an inventory of the region’s plants (other than crop
plants) produces a list of Old World species. And this takeover had largely been accomplished by 1600, only a century into colonization.
Likewise, although California is regarded as probably the richest center of biological diversity in what is now the United States, assembling a picture of its native grasslands is largely an exercise in paleobotany. California remained isolated and uncolonized until the mid-eighteenth century, yet adobe bricks from as early as 1769 show remnants of curly dock, sow thistle, and red stemmed filaree, all European weeds. That was but a modest beginning. A twentieth-century survey in the San Joaquin Valley found that invaders from Europe and Asia made up 63 percent of the vegetation in grasslands, 66 percent in woodlands, and 54 percent even in chaparral, the scrub brush habitat unique to California.
The same takeover occurred in the East. As early as 1638, a visitor to New England identified and catalogued twenty-two species of English weeds already at home in the colonies. One was indeed dandelion. Another was mullein, a species I battle now on my “wild” land in Montana.
Both weeds and introduced grasses were particularly hard on native grassland communities, a battle that continues to this day but one that was already mostly lost by the natives when it began. The invaders had long before coevolved with grazing sheep and cattle, and so could fill the voids that rampant overgrazing created, a relationship that epitomizes the partnerships that emerged across the advancing face of catastrophic agriculture. European colonization was biological warfare, much of it prosecuted before white eyes were present to record the battles. This strategy emerged full-blown and obvious late in the period of New Zealand, and while whites may not have understood fully what was happening, the native Maoris did. It is worth quoting Crosby’s summary of this at length:
In the 1850s, with the avalanche of the pakeha and associated species pouring ashore, more models of Maori extinction appeared. Exotic weeds ran like quicksilver among the roads into the bush. Native birds retreated as exotic cats, dogs, and rats advanced. The inadvertently imported Old World housefly
proved to be so effective at driving back the native bluebottle fly, hated by the pakeha because it learned to lay eggs in the flesh of sheep, that herdsmen took up the practice of carrying their own flies along with them into the back country in jars. The brown rats swept through the South Island, again exterminating all but a trace of the Maori rats, and in the 1860s were deep into the Southern Alps and growing to enormous sizes. Julius von Haast, a geologist who arrived in New Zealand in 1858, wrote Darwin that there was a proverb among the Maori that “as the white man’s fly drives away our own, and the clover kills our fern, so will the Maoris disappear before the white man himself.”