A Global History of Species Introduction and Invasion: Reconciling Historical and Ecological Paradigms
BRETT M. BENNETT
As this book has shown, one of the defining features of European imperialism was the purposeful introduction of foreign organisms, especially plants and animals, into every country and colony in the world. Europe’s nascent connection with most of the inhabited world—the Americas, Africa, and Asia—in the 1500s heralded a watershed era in global integration. During the following centuries, naturalists and governments supported efforts to classify species and move them around the world to serve human desires. Colonial ideologies justified, and sometimes required, the introduction of new species for food, fuel, shade, building materials, and more. Efforts to acclimatize new species for profit and pleasure peaked roughly between 1870 and 1939, the age of European high imperialism discussed in the previous chapters. Never before, and probably never again, will people purposefully introduce species into so many parts of the world on such a large scale. Although more total number of species are being introduced globally than ever before, the vast majority of these are unintentional invertebrate introductions rather than purposeful additions of plants or animals.1
Most of the new organisms that were introduced did not spread widely or cause problems, but a number did. Some of the worst consequences of these introductions—hordes of European rabbits (Oryctolagus cuniculus) in Australia and the like—will be familiar to most readers. The rabbit in Australia is one example of a species taken outside of its native range where it resided before human action that then became naturalized (sustains a local population) and invasive (has spread widely).2 Naturalized and invasive species are important components of the world’s ecosystems. The rate and intensity of species introductions and invasions has increased since the 1500s; a recent study suggests there is no “saturation point” yet in sight.3 The cat is now out of the bag (or more literally the boat) in places like Australia, where it has been introduced and cannot be eradicated.
Invasion ecologists, a subset of ecologists, have focused more attention on species introductions and invasion than any other discipline, but scholars in the humanities, especially environmental history and geography, have also studied these processes for many decades. Interest in introductions and invasions emerged in the 1980s in the sciences and humanities. Alfred Crosby published his seminal work Ecological Imperialism in 1986, only a few years after a team of researchers working with the Scientific Committee on Problems of the Environment started the first global survey of invasive species (the results were published in 1989).4 Since then, debates in ecology and the humanities have run parallel but rarely have scholars engaged substantially with findings from the other field. Most scholars in the sciences and history continue to conceive of introduction and invasion in starkly different terms, despite efforts to develop interdisciplinary perspectives.5
Scientific research on introduction and invasion assumes that invasion can be understood as an ecological process that can be induced from case studies. Finding a coherent theory for invasion has been illusive, but leading scholars have developed key concepts that inform scientific research, national legislation, and management practices.6 At the core of invasion ecology, researchers posit that nonnative species (which can include species from within a nation but from outside an ecosystem) are more likely than indigenous (those found in a region or site) species to harm the economy, displace indigenous ecological communities and individual species, and hinder ecological services, such as water. A small but nonetheless influential cohort of scientists holds different views on the underlying ecological dynamics and the extent of the negative impacts, but they are in the minority.7
Historians, and humanities researchers in general, have taken a different approach to species introduction and mobility. Research in the humanities is often critical of scientific perspectives, especially when they advocate management that involves changing the access to materials or the behavior of people, especially those who are poor or have less power.8 A sizable body of research shows how examples of efforts to control introduced and invasive species often reinforced unequal gender, power, and race relations.9 The influence of science and technology studies, postmodernism and poststructuralism, through Bruno Latour (discussed later) and others, has made many scholars critical of scientific expertise and any explanation invoking a universal theoretical principle that transcends time and space. Most researchers are wary of theories that span centuries and continents. There are exceptions, such as Alfred Crosby, but like scientific critics of mainstream invasion ecology views, they are in the minority.
This chapter suggests that a framework of globalization that both acknowledges an overall pattern of homogeneity without denying heterogeneity offers one way of reconciling aspects of scientific and humanities paradigms.10 The benefit of a globalization framework is that it requires the least changes to the methodology of each discipline, which is an obstacle to collaboration. Although every introduction or invasion is inherently local (they happen in a finite space and within discrete contexts), the vast majority of the world’s introductions and invasions are the consequence of post–1500 globalization.
Globalization is understood here as a process based on growing interconnections throughout different parts of the world driven primarily by imperialism, capitalism, and migration. The economic historian A. G. Hopkins has advanced a useful model of globalization that is based on key phases in world history.11 One benefit of this schema is that it offers clear signposts for nonhistorians. Hopkins divides post–1500 globalization into three overlapping phases—proto-globalization (1500–1850), modern globalization (1850–1950), and postcolonial globalization. Hopkins and others posit that globalization had multiple origins, but there were people (Europeans) and regions (Europe) that had a disproportionate influence in the early phases of globalization. Europe led the first stages of globalization through its trade, colonization, and industrialization, but in the first centuries its expansion was to a large extent built on older, existing trade networks in Asia, Africa, and to a lesser extent the Americas.
Studies of introduced and invasive species posit slightly different periodizations and geographies than Hopkins because their focus is on biotic globalization specifically. Alfred Crosby argued that there was a biological expansion of Europe from 900 to 1900, leading to colonization of places resembling Europe in its climate.12 John McNeill somewhat modified Crosby’s earlier dating by arguing that before 1500, Europe received more new species imports than it exported, although he agreed that by 1900, Europe once again imported rather than exported species.13 In an influential paper on invasive species, the ecologist Phillip Hulme traced a first phase of European expansion from 1500 to 1800; a second phase of increased invasions in Europe and North America based on the industrial revolution from around the 1850s; and a third phase, the era of globalization of the past three decades or so.14
Scholars studying the Anthropocene have also focused on globalization. Many of the key dates of globalization and the Anthropocene align broadly. Some scholars have dated the origins of the Anthropocene to the 1600s or 1800s, a dating consistent with work on globalization.15 Yet other scholars push the date forward and backward: some go as far back in time as the late Pleistocene, while others do not see it as beginning until the first atomic bomb was dropped.16 In terms of introduced and invasive species, it is clear that a key shift occurred somewhere between 1600 and 1900, rather than before or after. This chapter supports a more middle rather than earlier or later dating to the Anthropocene.
In the light of these findings, it is perhaps easiest and best to conceive of two stages in ecological globalization since the 1500s based on the rate and flow of introduced species. The first period, which dates roughly from 1500 to 1900, was shaped disproportionately by European imperialism and European-led long-distance trade. These processes caused a rapid increase in the diffusion of biota from different parts of the world. During this period there was a general increase in the number of species that were introduced and became established in every region of the world, but Eurasian flora and fauna disproportionately constituted the introduced and invasive species in nontropical areas as a result of settler colonialism.
The second phase, which started around 1850–1900 and continues today, has been characterized by the increase in invasions globally and a “catching-up” of invasions in Europe and tropical regions compared to other parts of the world. This dating corresponds with the beginning of Hopkins’s “modern globalization” phase. Hulme is right to point out the growing velocity of introductions from the second half of the twentieth century, but we should not forget that the late nineteenth and early twentieth centuries were periods of intense international trade; the late 1800s were only surpassed in terms of percentage of a country’s trade in the 1960s.17 Also, purposeful (rather than unintentional) introductions peaked in the late nineteenth and early twentieth centuries. Recent studies of invasive species in Europe point to 1900 as the beginning of a shift toward increased invasions in Europe, a region that previously lagged behind the temperate regions of the Americas and Australasia in terms of the total number and ecological impact of invasions.18
These are rough dates indicative of major global changes, and the dating may be earlier or later than changes for a specific place. Yet the trend is clear: there seems to be no “saturation” in the rate of introductions and the discovery of new invasions, something that suggests the process will continue to lead to a sort of ecological homogenization of many parts of the world.19 At the same time, as I discuss later, this overall homogenization must be understood as the outcome of the world’s great biological heterogeneity, which is based on distinct evolutionary histories of regions and particular taxa. Human activity and underlying ecological conditions have created heterogeneity—such as why rubber plantations developed in one country but not in another that could feasibly support them—so this model does not deny variation but nests it within a global context tending toward homogeneity.20
This periodization revives key parts of Alfred Crosby’s ecological imperialism thesis, which has received substantial criticism from many historians but has been more positively appraised in invasion ecology. Crosby argued that a combination of historical, geographical, and evolutionary factors allowed Europeans, and flora and fauna adapted to regions with temperate climates similar to Europe, to successfully colonize temperate regions of the Americas and Australasia. His views have often been interpreted as environmental determinism, when in fact he gave considerable attention to socioecological interactions through his concept of the “portmanteau biota,” an idea that has been used by other scholars and is largely justified based on extensive findings across a range of fields. Though many historians have challenged Crosby’s methodology and evidence, a number have continued to build on his work while also modifying his ideas.21
Crosby’s ideas on ecological change are highly relevant to understanding the past and present because they allow us to understand complex global change through a socioecological framework incorporating humans and nonhumans as actors. The geographer Paul Robbins drew explicitly from Crosby’s portmanteau biota framework in 2004 to analyze invasions at smaller spatial scales.22 Undoubtedly, some of Crosby’s views and periodizations should be revised based on recent historical research, but that does not mean his overall argument about introduced plants and animals is wrong. (There is an extensive debate about his epidemiological theory of disease, which falls outside of the scope of this epilogue). In his global study of guano, the world’s first widely used nitrogen-based fertilizer, Greg Cushman argues that Crosby’s thesis is useful to explain the first phase of settler colonialism but it becomes less relevant after there was an emergence of a fuel- and fertilizer-intensive industrial economy in the mid-1800s.23 The mid-1800s also corresponded to key historical changes, such as acclimatization and state science, so the slightly earlier dating (i.e., 1850s to 1870s rather than 1900) is in some ways better from a historical point of view because this is when many currently invasive species were introduced and began to spread.24
Somewhere between 1850 and 1900, the dynamics of globalization changed. The number of introduced species and those that became invasive became more equalized throughout the whole of the world, and especially in those regions connected by trade.25 The rate of introduction has continued to expand and equalize throughout the twentieth century.26 Regions such as Europe or the tropics that lagged in terms of recognized invasions are catching up to places such as Australia or North America, which experienced earlier and more extensive invasions.
Alfred Crosby’s 1986 book Ecological Imperialism is a useful entry point into this topic because it remains relevant today and is widely known by scholars in a variety of fields. Even critics are aware of its overall thesis, so it is perhaps the best way to communicate to scholars in multiple fields. For more than thirty years, Crosby’s book on ecological imperialism has remained a central reference point of historical research examining the ecological impact of European colonialism. Most historians expressed concerns about Crosby’s ideas rather than using them as a theory, but there has been a small but steady number of scholars who have extended his ideas. Scientists have shown far more sympathy for Crosby’s arguments.
Crosby was fascinated by how facets of European ecological and agricultural conditions were adapted in the temperate climate regions of the Americas and Australasia colonized by European settlers. He described these regions as neo-Europes because they had to a significant degree been modified through colonization to resemble Europe in many facets, including landscapes and ecologies. His book did not examine tropical regions and Africa, the Middle East, or Asia because Europeans never successfully replicated, in large numbers, European ecosystems and settlements in these places, with the exception of South Africa, a region he did not deal with in the book.
Crosby argued that there was an imbalance in plants exported from Europe outward that could not be explained merely by the fact that people brought more plants from that region compared to another. He did not give statistical evidence for this claim. Crosby pointed out that many Eurasian species seemed to succeed even in the absence of European settlers, whereas this seems to have happened very rarely with reverse flows. Why did this happen? Crosby wrote: “There is little or nothing intrinsically superior about Old World organisms compared with those of the Neo-Europes.” What differed was the evolutionary history of Old World organisms and the unique way in which so many plants were introduced into a region that had been transformed by colonists.
Crosby argued that a synergistic interaction between introduced species, including humans, was the primary explanation for the dominance of Eurasian species abroad and the relatively moderate impacts Europe experienced with introductions from the regions it colonized. Crosby argued that the evolutionary history of Eurasian species gave them unique advantages in highly human modified environments, such as areas of intense agriculture or grazing. Crosby wrote, “The co-evolution of Old World weeds and Old World grazers gave to the former a special advantage after the two spread in the Neo-Europes, and added on top of that was the advantage these plants had of having evolved along with the development of Old World agriculture.”27 Mammals succeeded for somewhat different reasons: a significant proportion of mammals thrived in new environments, such as Australia or New Zealand, because they lacked large predators, which is an argument explained to some degree by biogeography.
Crosby attributed the success rate of the portmanteau biota only partly to their evolutionary strategy (e.g., a weed growing among wheat). The sheer amount of species that were introduced around the same time shocked precolonial socioecological systems. Europeans came with what Crosby called the “portmanteau biota,” a plethora of organisms that had evolved with Europeans. He wrote, “The success of portmanteau biota and its dominant member, the European human, was a team effort by organisms that had evolved in conflict and cooperation over a long time.”28 The portmanteau biota included organisms with common evolutionary histories based on cohabituating in human-disturbed landscapes. These species interacted with each other in newly colonized environments in a way that, alongside human disturbance, promoted an increase in the number and rate of invasions. He described portmanteau biota as Europeans’ “fellow life forms, their extended family of plants, animals and microlife—descendants, most of them, of organisms that humans had first domesticated or that had first adapted to living with humans in the hearthlands of Old World civilization.… Where it ‘worked,’ where enough of its members prospered and propagated to create versions of Europe, however incomplete and distorted, Europeans themselves prospered and propagated.”29
It is not entirely easy to separate out the various strands of causality of Crosby’s arguments, something that has led to numerous somewhat misled critiques of his work, but a simple breakdown might look something like this: Crosby gave relatively equal weight to the traits of individual species that evolved in human-modified ecosystems, to geography, to the synergistic effect caused by the introduction of so many organisms into a single place at the same time, and to human action, through disturbance, colonization, and introduction. He gave broadly equal weight to evolution, ecology, biology, geography, and also human culture and history. The dramatic and popular style of his writing—the same reason his book was a success—sometimes limited its analytic clarity. Yet his writing was clear enough to inspire debate that continues to this day.
Crosby’s book has polarized readers since its debut. Although several historians have engaged positively with his ecological imperialism thesis, the majority of historians have been cautious or openly critical of his ideas. This section focuses on criticisms of Crosby’s work before discussing his generally positive reception in ecology.
Crosby’s thesis is controversial because he used evolutionary, ecological, and epidemiological theories to explain European colonization in the Americas and Australasia.30 Peter Coates chided Crosby for “coming close to reviving turn-of-the-century environmental determinism” (a reference to racialist thinking of geographers such as Ellsworth Huntington) and for denying European “culpability” in the destruction of indigenous ecosystems, populations, and lifestyles.31 Using biology and evolution in historical explanations is viewed by many historians as dangerous for various reasons, not least because environmental determinism was a key part of pre–World War II racial theories.
Even more historians have expressed alarm that Crosby supposedly downplayed the human role in ecological and demographic change. Not long after the publication of Crosby’s book, B. R. Tomlinson wrote an important rebuttal arguing that, “Much of the apparently ‘natural’ expansion of the plants and pathogens that occurred in the neo-Europes was closely linked to the process of human colonization and conquest.”32 Downplaying human agency is seen as justifying settler colonial violence and dispossession. It is often forgotten that Crosby wanted to downplay the idea that Europeans were superior as the primary explanation for why Europe rather than say, China, became the dominant region in the world.
Another constant criticism is that Crosby overemphasized the dominance of Eurasian species in the Americas and Australasia. Historical examples from a range of places—New Zealand, India, South Africa, the United States—demonstrate that there were many counterflows of crops (like potatoes and maize) as well as naturalized and invasive species that came from the so-called Neo-Europes.33 James Beattie argues that New Zealand was just as much the “empire of the rhododendron” because of the presence of Asian plants, as it was of the “empire of the dandelion,” which came from Eurasia.34 Europe also received many imports from the Neo-Europes. Peter Coates writes that the “most controversial immigrant fauna in Britain are all deliberate introductions from North America: gray squirrel, mink, muskrat, signal crayfish and ruddy duck.”35 Historians of South Africa, a region of European settlement that Crosby did not focus on, argue that a large proportion of introduced species came from the Americas or Australasia.36 Experts on India point to a similar fact.37 Some have gone so far to suggest that Crosby’s evidence of a Eurasian dominance in temperate climates is factually incorrect. William Beinart and Karen Middleton write, “in the period from 1500–1900, plant transfers may have been more evenly balanced than Crosby suggests.”38 Beinart and Middleton give no statistical breakdown for this claim. In fact, humanities scholars criticizing Crosby do not use statistics or findings from national field surveys.
Ecologists tend to have a more favorable view of Crosby. Moreover, there is a large body of research that was done without reference to Crosby (some invasion biologists know of Crosby, but many do not) that supports his ideas. Crosby’s views are compatible with key tenets of contemporary understandings of invasion dynamics based on three decades’ worth of empirical and theoretical research.
Just after the publication of Ecological Imperialism, the invasion biologist Daniel Simberlof wrote, “This is a provocative, novel hypothesis. It will be interesting to see how it fares when subjected to rigorous testing.”39 Francesco Di Castri, an Italian-born Chilean expert on invasion who helped direct the first global survey of invasive species by SCOPE in the 1980s, came to a similar conclusion as Crosby. Di Castri argued that Eurasian plants, and especially those from the European Mediterranean, seemed to be more invasive in New World habitats with Mediterranean climates than New World plants were invasive in the European Mediterranean.40 Di Castri agreed explicitly with Crosby on this point.41
Crosby’s point about asymmetry has been borne out by extensive surveys of invasive species.42 Even today, a disproportionate amount of naturalized and invasive species in the Americas and Australasia originate from Eurasia compared to other parts of the world. In 2013, Simberloff wrote that there is “no doubting the general pattern” of Old World species being disproportionately invasive in these regions.43 This dominance is particularly apparent in fields and agrarian environments rather than in closed forests and deserts.44 This asymmetry occurs globally, including in warmer Mediterranean climates as well as temperate climates, so Crosby’s theory can be expanded somewhat beyond his original intention.
Various explanations have been offered to explain this asymmetry. There is undoubtedly a strong historical component that reflects contingent events (e.g., one plant was brought to one place but not another; farmers or the state had greater capital to import more species and support them). Obviously, European migrants were, at least initially, more likely to bring species from Eurasia that they relied upon for food, materials, and aesthetics rather than from regions they did not know. The growth of global trade around the mid-1800s unleashed a much greater number of potential invasive species on the world, something that is recorded in surveys of invasions. According to the theory of propagule pressure, the larger the population, the more likely it is to become naturalized and then invasive.
Though necessary, the historical argument—that Europeans brought what they had on hand and the sheer number of them means that more became invasive—may not be sufficient. Simberloff weighted the competing evidence and claims to suggest that although history influenced this asymmetry, it alone did not explain the imbalance: “In sum, the sites and sources of invasions can often be explained by the history of human activities that move species. However, an apparent propensity of Eurasian species to invade elsewhere cannot wholly be attributed to history.”45 This is to say, there were unique socioecological dynamics associated with European colonization and there may be underlying biogeographic and evolutionary reasons as well.46 Two processes—invasional meltdown and the evolutionary history of Eurasian plants—have been invoked to account for this imbalance.
In an important article in the first issue of the journal Invasion Biology, David Simberloff and Betsy Von Holle build on Crosby directly by suggesting that invasion may be enhanced when there is an “invasional meltdown,” the establishment of multiple species populations that directly or indirectly facilitate a new invasion.47 Their argument challenged scholars who saw biotic resistance, the fitness of an ecosystem to resist invaders, as the primary way to measure the potential invasability of an area. Instead of focusing primarily on the resilience of an ecosystem, they posited that researchers need to study how introduced species created unique ecological dynamics that could synergistically work to facilitate invasion. After citing Crosby’s theory as one alternative model to biotic resistance because it emphasizes interspecies interactions among introduced species, they go on to offer a definition that is heavily indebted to Crosby’s portmanteau biota: “We suggest the term ‘invasional meltdown’ for the process by which a group of nonindigenous species facilitate one another’s invasion in various ways, increasing the likelihood of survival and/or of ecological impact, and possibly the magnitude of impact.”48 Their article, which has been cited extensively and is one of the key concepts created in the field of invasion biology, had the intended effect of turning attention toward the mutualistic dynamic of imported species.49
Crosby’s other ideas, such as the evolutionary changes associated with agriculture and cities, have been explored by scientists elsewhere. Research agrees with Crosby that the coevolution of weeds and pests may help explain the success of feral plants and animals in agrarian environments.50 Unique evolutionary conditions can be found outside of Eurasia. Reviewing global grass invasions, scholars have argued that Southern Africa is a key producer of the world’s invasive grasses (likely due to fire and other pressures), much like Australian trees (adapted to drought and fire and respond well to high levels of nutrients) contribute a disproportionate percentage of the world’s invasive trees.51 Asia produces a significant percentage of the invasive marine species in ports.52 These geographic and evolutionary factors must be a factor in how we analyze historical ecological change.
Crosby’s 1900 dating holds up remarkably well. Recent research indicates that Europe has been experiencing a growing rate of invasions since 1900. A European Union report issued in 2016 noted, “Results showed that the number of alien species in Europe has increased linearly over the past 100 years, leading to a fourfold increase in numbers since 1900.”53
The increase of total introductions and invasions has been explained using various theories. Some invasion researchers argue that species can “lag,” that is, reside in a place for a long time before spreading. Some ecologists argue for an “invasion debt” theory which proposes that the potential debt of invaders can be calculated by the total number of species in a place, their residency time, traits, and evolutionary background.54 There is a correlation between economic activity and introductions. Europe was in some ways a prime target for getting its ecological comeuppance because it had the world’s most extensive trade links.
This economic view reinforces the pioneering ideas of one of the “founders” of invasion ecology, Charles Elton, who saw invasions as a global phenomenon linked closely to increased trade and migration.55 Elton was focused on gleaning universal scientific concepts from “biological explosions” of invasive species rather than historicizing specific periods in the history of invasions.56 Elton’s belief in the cosmopolitan nature of invasions is confirmed by historical and economic research that shows an intensification of global trade and mobility during key periods (i.e., 1870 to 1914 and 1970s–present) from the late nineteenth century on. Invasion ecologists have shown that every part of the world has a greater number of naturalized and invasive species than ever before in known history.57 There is a general process of ecological homogenization. Most of the worst invasive species in one country are considered equally bad in another part of the world. Research in ecology suggests that there are key underlying geographic and evolutionary factors shaping invasion that are then influenced by historical contingency.
The tale of two Crosbys—a more critical reception in history and a more positive reception in science—raises important questions. Why did Crosby receive a more positive reception in the sciences than in the humanities? Did scholars in the humanities not know about developments in invasion ecology or did they just not think them to be relevant? And most important, how can this lesson inform future engagements between history and ecology?
The lack of engagement with scientific research on introduction and invasion reflects a wider distancing of the humanities and sciences since around the time Crosby wrote his book. Jo Guldi and David Armitage argue in The History Manifesto that, since the 1980s, the profession of history has suffered increasing neglect and a decline of public importance because the discipline pursued approaches that were often openly antagonistic to overtly materialist, empirical, or scientific viewpoints.58 Bruno Latour, Michel Foucault, and other key thinkers called on scholars to deconstruct positivism, scientism, and materialism inherited from the Enlightenment and Scientific Revolution. Scholars advocated theoretical positions that undermined traditional causality and popular scientific conceptions such as objectivity, facts, or truth.
For various reasons, it is increasingly difficult to sustain a model of history that rejects insights from the sciences and separates itself from questions of materiality. Yet how historians approach ecology is something that is being discovered on an individual-by-individual basis. Science (including ecology) is not usually taught in history PhD programs so historians, unless they take another degree, will need to be somewhat self-trained. The environmental historian William Beinart rightly admitted in his study of South African conservation that it “is very difficult for a historian untrained in science to evaluate … [scientific] studies.”59 He nonetheless concluded somewhat more optimistically: “but it is possible to discuss them in light of other evidence” that historians can know.60
The stumbling blocks to engaging with science are real, but they need not stop scholars from at least reading in other fields and putting science in a conversation with history, as Beinart did. Scholars in a variety of fields utilize knowledge from areas in which they are not experts.61 For instance, an ecologist who works on a multiauthored paper may not be familiar with the literature cited in the same paper by a mathematician or geologist. The team-based approach is foreign to most historians, who are locked into a single author and book-based model for tenure and promotion (at least that is the ideal for leading North American institutions, which have a disproportionate influence on scholarship).
In lieu of further formal study, historians can train themselves to learn the broad outlines of key debates and talk with experts outside of their area of specialty. Ecological concepts, at least in their more generalized forms, are not too difficult to comprehend. The terminology can be learned and experts who hold different opinions can be consulted. In my personal experience, ecologists are open to engagement and want to work with humanities scholars. The work of influential historians—Libby Robin, Jane Carruthers, and Simon Pooley, among others—shows that one can work with scientists without being a scientist.62
Historians often shy away from interdisciplinary engagements because it requires an epistemic shift away from one mode of evidence and reasoning to another one.63 Scientists (ecologists in this case) and historians use generalization and causality differently. Recognizing these differences is the first step to overcoming them to some degree. The historian John Lewis Gaddis suggests in his book on the writing of history that historians use “particular generalizations” from discrete events that are contextualized within their specific time and place.64 Scientists, he argues, use a different method that relies more on “universal generalizations” and theoretical models formed from examples. An ecologist studying invasion processes today is more likely to generalize present examples in understanding changes in the past, whereas a historian would suggest that each period of history must be taken on its own terms.
A wariness about making generalizations now characterizes much of the scholarship in the fields of global, imperial, and transnational history, where species introduction and invasion have most frequently been discussed.65 Many scholars in these fields have shifted toward using networked and other decentralized approaches to tracing mobility and flows to overcome older power analyses using concepts such as core and periphery.66 For instance, historians who criticize Crosby have offered no other systematic global model and thus they posit (explicitly or implicitly) that randomness and historical contingency characterized the dynamics of the era.67 Examples of counterflows are used to show that biotic exchange happened in other parts of the world. This is a point that Crosby understood perfectly well. Single case studies, discussed earlier, often focus on places (South Africa or India) or examples (noninvasive species requiring significant human support, such as Eucalyptus) well outside of the geographic limitations of Crosby’s thesis and thus cannot credibly be seen as a criticism of his specific claims. In all these cases, the exception does not actually prove the rule.
Using ecology, biogeography, or evolution to provide causal explanations for historical change runs contrary to how many (but not all) historians assign causality and agency in history.68 Prominent scholars of imperial and global history, such as Alan Lester, have argued that historians should not or cannot assign causation in history.69 In this view, causation—the discovery of putative origins of processes—is associated with an older mode of historical inquiry that focused on Europe as the origins of global capitalism, imperialism, democracy, and industrialization. In many ways, Crosby fits this older model: he sought to explain the dominance of Europeans in certain climates and environments using a similar “origins” structure. Ironically, Crosby sought to downplay European intellectual or cultural superiority by highlighting nonhuman drivers of Eurasia (including Asia), but his point has been lost over the decades. The position of this chapter is that historians need to at least engage with questions of causality in other fields and try to align with some of our thinking. There are significant problems associated with causality, but rejecting it entirely leaves us in a worse position. If we reject causality, even in its broad forms, we run the risk of seeing the world as contingent, a perspective that in some ways undermines the value of history as a didactic tool.
As demonstrated by chapters in this book, recent developments in the humanities—such as animal studies and posthuman thinking—have raised the prospect of assigning agency to nonhumans. Yet in many respects, this potential has been muted due to the lingering influence of certain strains of science and technology studies and poststructuralist, and postmodern thinking. Key ideas include: the asymmetry thesis (which does not judge the validity of historical claims), Latour’s actor-network theory (which denied the ability to use theory to assign causal priority to agents/objects that interact in what Latour described as a “network”), and constructivism (which posited that ideas are constructs not based on fundamental physical reality). Actor-network theory (ANT) has been widely used to trace human-nature entanglements in a way that does not privilege human agency.70 Not all scholars take these theories to their logical conclusion, but the influence of these intellectual strains has shaped an emergent field of environmental humanities that is often highly critical of the politics of ecology (as evidenced in the term “invasive species”).
There has been a pushback against the excesses of these views. Bruno Latour, who more than anyone shaped a critical stance toward scientific knowledge, wrote in a critique in 2004:
Entire Ph.D. programs are still running to make sure that good American kids are learning the hard way that facts are made up, that there is no such thing as natural, unmediated, unbiased access to truth, that we are always prisoners of language, that we always speak from a particular standpoint, and so on, while dangerous extremists are using the very same argument of social construction to destroy hard-won evidence that could save our lives. Was I wrong to participate in the invention of this field known as science studies? Is it enough to say that we did not really mean what we said?71
Latour did not reject everything he wrote about, but he rightly suggested that theoretical lenses are tools for understanding a complex world, not ontological realities unto themselves. Despite Latour’s plea, some fields (e.g., history of science and environmental humanities) influenced by his work from the 1980s and 1990s adhere somewhat closer to his earlier rather than contemporary views on scientific knowledge.
In a similar vein, Guldi and Armitage argue that the lack of engagement with the sciences and social sciences is problematic because it has meant that historians have less relevance in public debates. Even though there are pitfalls in trying to trace patterns across long periods of time, they argue that historians are well equipped to do this because they are aware of the importance of context. None of these scholars, from Guldi to Latour, advocates using science as “truth,” but they suggest that we must engage seriously with scientific “matters of concern,” such as global warming and invasive species, raised by the scientific community. This chapter echoes these sentiments and hopes to encourage more historians to think both constructively as well as critically about science.
How do we all work together when the humanities and sciences view generalization, causation, and evidence differently? We can turn both to pragmatism and constructivism, traditions that urge us to recognize that all disciplinary knowledge is a particular lens onto the world rather than the world itself. The production of discipline-specific knowledge should be a means to an end product that must be negotiated with other disciplines and social groups to enact ideas into policy and action. History should not only be read by historians. Disciplines are not useful if they keep us from engaging with other disciplines or the public. By no means does this mean that historians should quit trying to contextualize periods of history. Far from it. Guldi and Armitage rightly point out these unique contextual skills and research abilities—skills based on a focus on particulars as well as generalizations—are required when assessing long-term patterns. But doing good interdisciplinary work is going to require many humanists to at least engage constructively, not only critically, with scientific concepts and scientists.
Historians should write research for their peers but also engage with other disciplines using the concepts in those fields while fully recognizing their limitations. Scientists and many social scientists increasingly conceive of a landscape in terms that capture its range of influences, from human action all the way down to basic biophysical processes. Historians generally shy away from making universal generalizations, but we should not be afraid to learn about the evidence and theories of other fields in order to create hypothetical historical scenarios. For instance, research on the population dynamics of current plant invasions and genetic analysis of species (which can tell what region of a foreign country they come from and even when) can be used to think about historical events where we have no written, oral, or visual records. The “social” in socioecological recognizes that natural systems are inherently interlinked intellectually and materially with humans. This conceptual tool offers historians the space to engage directly with other scholars. There are legitimate critiques of this approach, but it would be a shame if we let theoretical purity stop historians from working with scientists directly on issues of common concern.
Scholars seeking to understand the history, patterns, and possible futures of biotic globalization should engage more with findings from history, ecology, and a variety of other disciplines (e.g., geography) when developing macroscale historical interpretations. A large body of ecological research suggests that there were unique ecological patterns associated with the expansion of European settler colonies. The dating of 1900, first put forward by Crosby, has been confirmed subsequently in ecology and history as a useful period to mark the shift from one phase of ecological globalization to another. That ecologists find consistent patterns of convergent ecological changes throughout the world suggests that biologic globalization as a process was based solely on human agency. It is not sufficient to discredit global patterns with single case studies of microhistory. The challenge for those who disagree with Crosby or science-informed interpretations is to offer an alternative hypothesis that engages directly (even if critically) with the argument and the evidence discussed and put forth in this chapter.
1. Phillip Hulme, “Trade, Transport and Trouble: Managing Invasive Species Pathways in an Era of Globalization,” Journal of Applied Ecology 46, no. 1 (2009): 10–18.
2. For definitions, see David M. Richardson, Petr Pyšek, Marcel Rejmánek, Michael G. Barbour, F. Dane Panetta, and Carol J. West, “Naturalization and Invasion of Alien Plants: Concepts and Definitions,” Divers Distribution 6 (2000): 93–107. In this epilogue I use the terms “naturalization” to denote a species that has been introduced and has a population within a new region and “invasion” to refer to self-reproducing species that colonize in areas where there is no historical record of their occupation. Many historians may prefer to use other terms, but these terms are useful for their technical description (i.e., something that is introduced, something that establishes itself, and something that reproduces) irrespective of impact.
3. Richard N. Mack, Daniel Simberloff, W. M. Lonsdale, Harry Evans, Michael Clout, and Fakhri A. Bazzaz, “Biotic Invasions: Causes, Epidemiology, Global Consequences, and Control,” Ecological Applications 10, no. 3 (June 2000): 689–710. For a historian’s view on these challenges, see William Beinart, “Bio-invasions, Biodiversity, and Biocultural Diversity: Some Problems with These Concepts for Historians,” RCC Perspectives 1 (2014): 75–80, 75.
4. James A. Drake, Harold A. Mooney, F. Di Castri, R. H. Groves, F. J. Kruger, M. Rejmánek, and M. Williamson, eds., Biological Invasions: A Global Perspective (Chichester, UK: Wiley, 1989).
5. Ana S. Vaz, Christoph Kueffer, Christian A. Kull, David M. Richardson, Stefan Schindler, A. J. Muñoz-Pajares, Joana R. Vicente, João Martins, Cang Hui, Ingolf Kühn, and João P. Honrado, “The Progress of Interdisciplinarity in Invasion Science,” Ambio-stockholm-46 4 (2017). Also see Cang Hui and David Richardson, Invasion Dynamics (Oxford: Oxford University Press, 2017), chap. 1; David Richardson, Jane Carruthers, Cang Hui, Fiona A. C. Impson, Joseph T. Miller, Mark P. Robertson, Mathieu Rouget, Johannes J. Le Roux, and John R. U. Wilson, “Human-Mediated Introductions of Australian Acacias—A Global Experiment in Biogeography,” Diversity and Distributions 17, no. 5 (2011): 771–87.
6. For the most up-to-date survey, see Richardson and Hui, Invasion Dynamics.
7. See one critical opinion: Mark A. Davis, “Don’t Judge Species on Their Origins,” Nature International Journal of Science 474 (July 2011), 153–54, http://
8. The list is not exhaustive, but representative articles from different fields include: Susanna Lidström, Simon West, Tania Katzschner, M. Isabel Pérez-Ramos, and Hedley Twidle, “Invasive Narratives and the Inverse of Slow Violence: Alien Species in Science and Society,” Environmental Humanities 7, no. 1 (2016): 1–40; Jonathan Clark, “Uncharismatic Invasives,” Environmental Humanities 6, no. 1 (2015): 29–52; Charles Warren, “Perspectives on the ‘Alien’ versus ‘Native’ Species Debate: A Critique of Concepts, Language and Practice,” Progress in Human Geography 31, no. 4 (2007): 427–46; Jean Comaroff and John L. Comaroff, “Naturing the Nation: Aliens, Apocalypse and the Postcolonial State,” Journal of Southern African Studies 27, no. 3 (2001): 627–51.
9. This is a representative but not exhaustive list of studies. See Lance van Sittert, “ ‘Our Irrepressible Fellow-Colonist’: The Biological Invasion of Prickly Pear (opuntia Ficus-Indica) in the Eastern Cape C. 1890–C. 1910,” Journal of Historical Geography 28, no. 3 (2002): 397–419; William Beinart and Luvuyo Wotshela, Prickly Pear: The Social History of a Plant in the Eastern Cape (Johannesburg: Wits University Press, 2011); Jodi Frawley and Iain McCalman, “Invasion Ecologies: The Nature/Culture Challenge,” in Rethinking Invasion Ecologies from the Environmental Humanities, edited by Jodi Frawley and Iain McCalman (Oxford: Routledge, 2014), 3–14; Libby Robin and Jane Carruthers, “National Identity and International Science: The Case of Acacia,” Historical Records of Australian Science 2, no. 1 (2012): 34–54; Simon Pooley, “Pressed Flowers: Notions of Indigenous and Alien Vegetation in South Africa’s Western Cape, c. 1902–1945,” Journal of Southern African Studies 36, no. 3 (2010): 599–618; Jane Carruthers, Libby Robin, Johan Hattingh, Christian Kull, Haripriya Rangan, and Brian W. van Wilgen, “A Native at Home and Abroad: The History, Politics, Ethics and Aesthetics of Acacia,” Diversity and Distributions 17, no. 5 (2011): 810–21; Natasha Nongbri, “Plants Out of Place: The ‘Noxious Weeds’ Eradication Campaign in Colonial South India,” Indian Economic & Social History Review 53, no. 3 (2016): 343–69; Peter Coates, American Perceptions of Immigrant and Invasive Species: Strangers on the Land (Berkeley: University of California Press, 2006).
10. Mark Davis used the term in 2003. This article does not advance or criticize Davis and uses the term neutrally. Mark A. Davis, “Biotic Globalization: Does Competition from Introduced Species Threaten Biodiversity?,” Bioscience 53, no. 5 (May 2003).
11. See A. G. Hopkins, ed., Globalisation in World History (London: Pimlico, 2002).
12. Alfred W. Crosby, Ecological Imperialism: The Biological Expansion of Europe, 900–1900 (Cambridge: Cambridge University Press, 1986; 2nd ed. 2004).
13. J. R. McNeill, “Europe’s Place in the Global History of Biological Exchange,” Landscape Research 28, no. 1 (2003): 33–39.
14. Hulme, “Trade, Transport and Trouble,” 10–18.
15. For 1600s, see Lewis and Maslin. Also see Wolfgang Lucht, “The Human Planet: How We Created the Anthropocene,” Nature Journal of Science 558 (June 2018): 26–27, https://
16. Jan Zalasiewicz, Mark Williams, Alan Haywood, and Michael Ellis, “The Anthropocene: A New Epoch of Geological Time?,” Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 369 (2011): 835–41.
17. World Trade Organization, World Trade Report 2013 (Lanham, MD: Bernan Press, 2013), 47.
18. F. Essl, S. Dullinger, W. Rabitsch, P. E. Hulme, K. Hülber, V. Jarošík, and I. Kleinbauer, “Socioeconomic Legacy Yields an Invasion Debt,” Proceedings of the National Academy of Sciences of the United States of America 108, no. 1 (2010).
19. See F. Essl et al., “Socioeconomic Legacy,” 203–7. For further development, see Rouget Mathieu et al., “Invasion Debt—Quantifying Future Biological Invasions,” Diversity and Distributions 22, no. 4 (2016): 445–56.
20. Corey Ross, “Developing the Rain Forest: Rubber, Environment and Economy in Southeast Asia,” in Economic Development and Environmental History in the Anthropocene: Perspectives on Asia and Africa, edited by Gareth Austin (London: Bloomsbury Academic, 2017), 199–218.
21. Notable examples include Elinor Melville, A Plague of Sheep: Environmental Consequences of the Conquest of Mexico (Cambridge: Cambridge University Press, 1994) and Greg Cushman, Guano and the Opening of the Pacific World: A Global Ecological History (Cambridge: Cambridge University Press, 2013), xvi.
22. This global-scale focus builds on and agrees with Paul Robbins’s analysis of how the concept of “portmanteau biota” combines natural and cultural dynamics into a coherent model. See Paul Robbins, “Comparing Invasive Networks: Cultural and Political Biographies of Invasive Species,” Geographical Review 94, no. 2 (2004): 139–56, 143.
23. Cushman, Guano and the Opening of the Pacific World, 17–18. See his comments on Crosby on 71, 110.
24. This is a key point in F. Essl, “Socioeconomic Legacy Yields an Invasion Debt.”
25. For a discussion of the intensity of economic integration and human migration in the late nineteenth and early twentieth centuries, see “Introduction” in Michael Bordo, Alan M. Taylor, and Jeffrey G. Williamson, Globalization in Historical Perspective (Chicago: University of Chicago Press, 2007). See the threefold stages of A. G. Hopkins, “Is Globalization Yesterday’s News,” Itinerario 41, no. 1 (2017): 109–28.
26. Hulme, “Trade, Transport and Trouble,” 11, fig. 1.
27. Hulme, “Trade, Transport and Trouble,” 11, fig. 1.
28. Hulme, “Trade, Transport and Trouble,” 293.
29. Hulme, “Trade, Transport and Trouble,” 89.
30. See the discussion by Dipesh Chakrabarty, “The Climate of History: Four Theses,” Critical Inquiry 35, no. 2 (Winter 2009): 197–222, 214–15.
31. Peter Coates, Nature: Western Attitudes since Ancient Times (Oxford: Blackwell Press, 1998), 102.
32. B. R. Tomlinson, “Empire of the Dandelion: Ecological Imperialism and Economic Expansion, 1860–1914,” Journal of Imperial and Commonwealth History 26, no. 2 (1998): 84–99, 90.
33. Tomlinson, “Empire of the Dandelion,” 90.
34. James Beattie, “ ‘The Empire of the Rhododendron’: Reorienting New Zealand Garden History,” in Making a New Land: Environmental Histories of New Zealand, edited by Tom Brooking and Eric Pawson (Dunedin, New Zealand: Otago University Press, 2013), 241–57.
35. Peter Coates, American Perceptions of Immigrant and Invasive Species: Strangers on the Land (Berkeley: University of California Press, 2006), 24.
36. Lance van Sittert, “ ‘The Seed Blows about in Every Breeze’: Noxious Weed Eradication in the Cape Colony, 1860–1909,” Journal of Southern African Studies 26, no. 4 (2000): 655–74; Brett M. Bennett, “Naturalising Australian Trees in South Africa: Climate, Exotics and Experimentation,” Journal of Southern African Studies 37, no. 2 (2011): 265–80.
37. Natasha Nongbri, “Plants Out of Place: The ‘Noxious Weed’ Eradication Campaign in Colonial Southern India,” Indian Economic & Social History Review 53, no. 3 (2016): 343–69, 346.
38. William Beinart and Karen Middelton, “Plant Transfers in Historical Perspective: A Review Article,” Environment and History 10, no. 1 (February 2004): 8.
39. Daniel Simberloff, “Ecological Imperialism: The Biological Expansion of Europe, 900–1900, Alfred Crosby,” Quarterly Review of Biology 62, no. 2 (1987): 223.
40. F. Di Castri, “An Ecological Overview of the Five Regions with a Mediterranean Climate,” in Biogeography of Mediterranean Invasions, edited by R. H. Groves and F. Di Castri (Cambridge: Cambridge University Press, 1991), 1–16; F. Di Castri, “History of Biology Invasions with Special Emphasis on the Old World,” in Biology Invasions: A Global Perspective, edited by J. A. Drake et al. (Chichester, UK: Wiley, 1989), 1–29.
41. Di Castri, “History of Biology Invasions,” 8.
42. Richard H. Groves, “The Biogeography of Mediterranean Plant Invasions,” in Biogeography of Mediterranean Invasions, edited by Richard H. Groves and F. Di Castri (Cambridge: Cambridge University Press), 427–38; V. H. Heywood, “Patterns, Extents and Modes of Invasion by Terrestrial Plants,” in Biology Invasions: A Global Perspective, edited by J. A. Drake et al. (Chichester, UK: Wiley, 1989), 31–60; P. Pyšek, “Is There a Taxonomic Pattern to Plant Invasions?,” Oikos 82 (1988): 282–94; Jason Fridley, “Of Asian Forests and European Fields: Eastern U.S. Plant Invasions in a Global Floristic Context,” PloS One 3, 11 (2008): e3630.
43. Daniel Simberloff, Invasive Species: What Everyone Needs to Know? (Oxford: Oxford University Press, 2013), 29.
44. Ironically, Fridley in “Of Asian Forests and European Fields” agrees with Crosby but misrepresents Crosby’s actual arguments by suggesting that Crosby did not give weight to biogeography, which he certainly did, or to invasions from other parts of Eurasia.
45. Simberloff, Invasive Species, 29–30.
46. Simberloff, Invasive Species, 36.
47. Daniel Simberloff and Betsy Von Holle, “Positive Interactions of Nonindigenous Species: Invasional Meltdown?,” Biological Invasions 1, no. 1 (1999): 21–32.
48. Simberloff and Von Holle, “Positive Interactions,” 22.
49. Cang Hui and David M. Richardson, Invasion Dynamics (Oxford: Oxford University Press, 2017), 8, 12.
50. See Fridley, “Of Asian Forests and European Fields.”
51. For grasses, see Veron Visser, John R. U. Wilson, Lyn Fish, Carly Brown, Garry D. Cook, and David M. Richardson, “Much More Give than Take: South Africa as a Major Donor but Infrequent Recipient of Invasive Non-Native Grasses,” Global Ecology and Biogeography 25, no. 6 (2016): 679–92. For trees, see Marcel Rejmánek, “Invasive Trees and Shrubs: Where Do They Come From and What We Should Expect in the Future?,” Biological Invasions 16, no. 3 (2014): 483–98.
52. James T. Carlton, “Pattern, Process, and Prediction in Marine Invasion Ecology,” Biological Conservation 78, no. 1–2 (October–November 1996).
53. W. Rabitsch, Piero Genovesi, Riccardo Scalera, Katarzyna Biała, Melanie Josefsson, and Franz Essl, “Developing and Testing Alien Species Indicators for Europe,” Journal for Nature Conservation 29 (2016): 89–96. Also see “Invasive Alien Species in Europe: New Framework Shows Scale and Impact Increasing,” 451, http://
54. Mathieu Rouget, Mark P. Robertson, John R. U. Wilson, Cang Hui, Franz Essl, Jorge L. Renteria, and David M. Richardson, “Invasion Debt—Quantifying Future Biological Invasions,” Diversity and Distributions 22, no. 4 (2016): 445–56, https://
55. Elton is often seen as the intellectual “founder” of invasion biology, even though the modern field developed primarily in the 1980s and 1990s. See Dave Richardson, ed., Fifty Years of Invasion Ecology: The Legacy of Charles Elton (Chichester, UK: Wiley-Blackwell, 2011). The work of Matthew Chew has situated Elton’s work and ideas within the context of the post–World War II Cold War era. Matthew Chew, “Ending with Elton: Preludes to Invasion Biology” (PhD diss., Arizona State University, 2006). See Matthew Chew, “A Picture Worth Forty-One Words: Charles Elton, Introduced Species, and the 1936 Admiralty Map of British Empire Shipping,” Journal of Transport History 35, no. 2 (2014): 225–35.
56. Elton’s seven initial examples of biological “explosions” only included two species from Europe, with the other five coming from Asia (2), North America (2), and Africa (1). Elton listed the Chinese mitten crab (Eriocheir sinensis), the sea lamprey (Petromyzon marinus) from North America, cord-grass (Spartina townsendii) from England, muskrat (Ondatra zibethica) from North America, European starling (Sturnus vulgaris), Chestnut blight (Endothia parasitica) from China, and African mosquito (Anopheles gambiae).
57. Hanno Seebens et al., “No Saturation in the Accumulation of Alien Species Worldwide,” Nature Communications 8 (2017).
58. Jo Guldi and David Armitage, The History Manifesto (Cambridge: Cambridge University Press, 2014).
59. William Beinart, The Rise of Conservation in South Africa: Settlers, Livestock, and the Environment 1770–1950 (Oxford: Oxford University Press 2003), 376.
60. Beinart, The Rise of Conservation in South Africa, 376.
61. Simon Pooley, J. A. Mendelsohn, E. J. Milner-Gulland et al., “Hunting Down the Chimera of Multiple Disciplinary,” Conservation Biology 28, no. 1 (February 2014): 22–32.
62. Simon Pooley, Burning Table Mountain: An Environmental History of Fire on the Cape Peninsula (Claremont, South Africa: UCT Press, 2015); Bella S. Galil, Agnese Marchini, and Anna Occhipinti-Ambrogi, “Mare Nostrum, Mare Quod Invaditur—The History of Bioinvasions in the Mediterranean Sea,” in Histories of Bioinvasions in the Mediterranean, edited by Ana Isabel Queiroz and Simon Pooley, vol. 8, Environmental History (2018); see Jane Carruthers and Libby Robin, “Taxonomic Imperialism in the Battles for Acacia: Identity and Science in South Africa and Australia,” Transactions of the Royal Society of South Africa 65, no. 1 (2010): 48–64, among others.
63. J. Fisher, A. D. Manning, W. Steffen, D. B. Rose, K. Daniell, A. Felton, and S. Garnett, “Minding the Sustainability Gap,” Trends in Ecology & Evolution 22 (2007): 621–24.
64. Gaddis Lewis, The Landscape of History: How Historians Map the Past (Oxford: Oxford University Press, 2004), 63.
65. Brett Bennett and Gregory Barton, “Generalizations in Global History: Dealing with Diversity without Losing the Big Picture,” Itinerario 41, no. 1 (2017): 15–25, 16–18.
66. See Brett Bennett and Joseph Hodge, eds., Science and Empire: Knowledge and Networks of Science across the British Empire, 1800–1970 (Basingstoke, UK: Palgrave Macmillan, 2011).
67. Beinart and Middelton, “Plant Transfers,” offers perhaps the most coherent response but this still does not posit a coherent global theory.
68. See Gaddis, The Landscape of History, 64. There is a huge variety of ways historians conceive of causation in history, but the salient point is that scholars criticizing Crosby have generally adhered to the positions described. Scholars in a variety of fields, especially big history, deep history, and environmental history, give agency and causation to physical and biological forces.
69. Bennett and Barton, “Generalizations in Global History,” 16–18.
70. For a discussion of the meanings of network, see Bennett and Hodge, Science and Empire. For research utilizing a networked approach in this sense, see Jodi Frawley, “Prickly Pear Land: Transnational Networks in Settler Australia,” Australian Historical Studies 38, no. 130 (2007): 373–88; Frawley, “A Lucky Break: Contingency in the Storied Worlds of Prickly Pear,” Continuum 28, no. 6 (2014): 760–73.
71. Bruno Latour, “Why Critique Has Run Out of Steam: From Matters of Fact to Matters of Concern,” Critical Inquiry 30, no. 2 (2004): 225–48, 227.