Extinction and biodiversity

A historical perspective

Authored by: David Sepkoski

The Routledge Handbook of Philosophy of Biodiversity

Print publication date:  September  2016
Online publication date:  October  2016

Print ISBN: 9781138827738
eBook ISBN: 9781315530215
Adobe ISBN: 9781315530208




Why care about biodiversity? This is a question that could be answered from many perspectives – economic, philosophical, pragmatic, aesthetic, ethical, etc. – and many of the essays in this volume explore those arguments that can be and have been mustered in favor of preserving the diversity of life on Earth. But it is also a question that demands a historical answer: not so much why should we care about biodiversity so much as why do we now, why has biodiversity preservation only emerged as a fairly recent topic of global political and scientific concern, and what has changed over the past 150 years or so in cultural awareness and biological understanding that has brought this about? It would be tempting to think that concern for the diversity of life is a self-evident value, requiring little justification. It may well be that arguments can be made that biodiversity has just such intrinsic value from a philosophical standpoint, but the simple historical fact is that Western society has not always recognized this. That is to say, the past 200 years or so of biological thought reveals a shifting landscape of opinion concerning the value and even the very existence of the category we would now call “biodiversity.” It is only in the past fifty years or so that scientists have recognized that the study of biological diversity merits special attention and methods – whether in ecological or geological context – and even more recently that its current preservation has become a political issue.

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Extinction and biodiversity

Why care about biodiversity? This is a question that could be answered from many perspectives – economic, philosophical, pragmatic, aesthetic, ethical, etc. – and many of the essays in this volume explore those arguments that can be and have been mustered in favor of preserving the diversity of life on Earth. But it is also a question that demands a historical answer: not so much why should we care about biodiversity so much as why do we now, why has biodiversity preservation only emerged as a fairly recent topic of global political and scientific concern, and what has changed over the past 150 years or so in cultural awareness and biological understanding that has brought this about? It would be tempting to think that concern for the diversity of life is a self-evident value, requiring little justification. It may well be that arguments can be made that biodiversity has just such intrinsic value from a philosophical standpoint, but the simple historical fact is that Western society has not always recognized this. That is to say, the past 200 years or so of biological thought reveals a shifting landscape of opinion concerning the value and even the very existence of the category we would now call “biodiversity.” It is only in the past fifty years or so that scientists have recognized that the study of biological diversity merits special attention and methods – whether in ecological or geological context – and even more recently that its current preservation has become a political issue.

It turns out that one of the key components of the biological understanding of diversity – and of changes in its valuation – has been how biologists and paleontologists have conceptualized and understood extinction. One of the most effective rhetorical tools in the biodiversity preservation movement has been the association of the current biodiversity crisis with a “sixth mass extinction” (Leakey and Lewin 1995; Kolbert 2014). This idea developed out of paleontologists’ identification of five major mass extinctions – the so-called “big five” – in the history of life, events during which anywhere from 70 to 98 percent of standing diversity was extinguished in a geological instant (Raup and Sepkoski 1982). But the concept of mass extinction itself is a relatively new feature of biology: before the 1970s it was an idea more associated with the lunatic fringe than with serious science, and it was not until the 1980s (prompted by the discovery of physical evidence of the bolide impact that killed the dinosaurs some 65 million years ago) that paleontologists have been able to present concrete proof that catastrophic extinctions have occurred, or to model their ecological and evolutionary effects (Sepkoski 2012). For most of the history of modern biology, it has been assumed that extinction is a slow, gradual process that operates over very long periods of time, and which is in equilibrium with replacement via the evolution of new species. We have become so accustomed, in recent decades, to think of the foothold of life on Earth (including our own species’) as tenuous that it is easy to forget that we have not always perceived it so.

The simple reason that extinction is so closely related to beliefs about the value of biodiversity is that, as a culture, we tend to value most what we fear losing. Concern for individual endangered species or regret over their passing – the California condor, the passenger pigeon, the great auk – dates well back into the nineteenth century (Barrow 2009). But the preservation of particular species (which, not coincidentally, are usually associated with romantic or aesthetic attachments) is not the same thing as valuing all organisms, or regarding diverse environments as being essential for our own survival. Anxiety about the loss of such individual species has long motivated conservation efforts, but it is fear over losing many species in a short period of time – and not only the pretty or valuable ones – that motivates the recent biodiversity movement (Takacs 1996; Farnham 2007). This concern has, in recent decades, been formalized in agreements such as the 1992 UN Convention on Biological Diversity, where more than 150 nations affirmed “the intrinsic value of biological diversity” and pledged to foster its protection (UN 1992: 1). That strong association of biological diversity with “intrinsic value” also animates discussions of other kinds of diversity – linguistic, ethnic, cultural – that have gained momentum since the early 1990s as well (Sepkoski 2015). A decade after the UN Convention on Biological Diversity, UNESCO produced a “Universal Declaration on Cultural Diversity” which framed cultural diversity in exactly the same language as the earlier document had presented biological diversity: as “a living, and thus renewable treasure that must not be perceived as unchanging but as a process guaranteeing the survival of humanity …. [C]‌ultural diversity is as necessary for humankind as biodiversity is for nature” (UNESCO 2002).

If, as I have argued, biodiversity is only a fairly recently recognized value, then how did this transformation come about, and what earlier value system did it replace? These are the questions I will address in this chapter. I will begin with the nineteenth-century acceptance of extinction as a natural – and fairly common – occurrence, placing Victorian-era biological views of extinction in their cultural context. I argue that, for most of the nineteenth century, biological diversity was not recognized as a phenomenon worth studying or preserving in its own right because biologists understood the natural world to be in constant equilibrium where, as Carl Linnaeus had put it in 1762, “the death and destruction of any one thing should always be subservient to the restitution of another” (Linnaeus 1762: 40). Perhaps not surprisingly, this view was often taken as implicit justification for activities by Europeans and their colonists that led to the eradication of native peoples, flora, and fauna during an era of imperialist expansion (Brantlinger 2003).

It was only during the second half of the twentieth century that the idea of mass extinctions became scientifically respectable, and consequently that the notion of a biodiversity “crisis” could emerge. This change in scientific consensus was preceded and accompanied by a series of dramatic cultural and political shifts that brought about a new climate of “threat” or anxiety in the West. Two world wars, Hiroshima and Auschwitz, the Doomsday Clock, Silent Spring and Three Mile Island, Vietnam and the student protests of the 1960s, and a host of other factors helped produce what historian Eric Hobsbawm has called “the Age of Catastrophe” (Hobsbawm 1994). In the mid-1980s, this heightened sense of cultural anxiety was a receptive context for the introduction of two important scientific developments. The first was the discovery in 1980 by Luis and Walter Alvarez that the dinosaurs had become extinct suddenly as the result of a catastrophic collision with an asteroid or comet. This received considerable media interest and led to further study of mass extinctions in the geological past, which elevated mass extinction to dramatic public attention (Sepkoski 2012: ch. 9). Parallels between the Alvarez impact hypothesis and the projected aftermath of a nuclear exchange were missed neither by the public nor scientists: in fact, the much-discussed “nuclear winter” scenario was developed on the basis of climate models first proposed for impact events (Badash 2009).

The second event was the official introduction of “biodiversity” into scientific and political vocabulary. In 1986, the botanist Walter G. Rosen and the entomologist and ecologist E. O. Wilson organized a “National Forum on BioDiversity” in Washington, DC. Sponsored by the National Academy of Sciences and the Smithsonian Institution, this conference brought together experts in biology, ecology, paleontology, economics, and public policy for a summit to consider broad threats to biological diversity caused by human action (or inaction). While this was not the first call to protect the environment or endangered species from the consequences of industrialization, pollution, overpopulation, and the like, it dramatically changed both the tone of the conversation and the political stakes involved. Not only did this event introduce the term “biodiversity” to common currency, it also made the link between extinction and biodiversity conservation clear from the very start. Writing in the introduction to the published conference proceedings, Wilson commented that “The current reduction of diversity seems destined to approach that of the great natural catastrophes at the end of the Paleozoic and Mesozoic eras – in other words, the most extreme in the past 65 million years” (Wilson 1988a: 11–12). From this point forward, our current biodiversity crisis became inextricably linked to our understanding of the major mass extinctions of the geological past – the “sixth extinction” trope was born (Leakey and Lewin 1995).

Victorian extinction

The phenomenon of extinction first received serious scientific attention through the work of the French naturalist Georges Cuvier (1769–1832) in the first decades of the nineteenth century. Prior to this point, European and American naturalists and savants had debated whether god would allow any species to be destroyed, as such an event was seen to potentially violate the divinely ordained balance of nature. Famously, when confronted with recently discovered fossils of the strange beast dubbed “mammoth,” Thomas Jefferson expressed confidence that living specimens would be found in the unexplored American continent, since, as he put it in his Notes on the State of Virginia, “such is the balance of nature, that no instance can be produced, of her having permitted any one race of her animals to become extinct; of her having formed any link in her great work so weak as to be broken” (Jefferson 1801: 77).

Mounting fossil evidence, however, quickly convinced naturalists that the former world had indeed been populated by creatures that no longer existed, but the question of extinction was not immediately settled. Jean-Baptiste Lamarck (1744–1829), for example, rejected the idea of extinction, favoring instead an evolutionary process that had molded organisms into their current forms. Lamarck’s position was directly challenged by Cuvier, who interpreted huge fossil deposits in the quarries outside of Paris as evidence of great “revolutions” or catastrophic mass extinctions that he believed punctuated episodes in Earth’s history (Rudwick 1997). One irony for our story, then, is that while the first major theory of extinction recognized mass extinctions as a regular feature of the history of life, Cuvier’s “catastrophism” was decisively rejected by most of the scientific community for the next 150 years or more (Rudwick 2005). The reasons for this are complex, but one major consideration was likely the fact that Cuvier’s theory of episodic catastrophes upset longstanding beliefs about the balance or economy of nature found in Judeo-Christian and even Classical teachings. 1 It is notable that, even when Darwin introduced his supposedly revolutionary notion of evolution via natural selection, he nonetheless preserved a fairly conservative view of the equilibrium of nature (as I will discuss below) (Cuddington and Ruse 2004).

In Britain, especially, it was taken for granted throughout most of the nineteenth century that when extinction did take place (and by the 1820s and 1830s there was mounting evidence for this fact) the finely tuned balance of nature was never upset (Parkinson 1804). This commitment to a stable natural equilibrium prevented most naturalists from granting the possibility of mass extinctions. Charles Lyell (1797–1875), the great Scottish pioneer of modern geology and close friend of Darwin’s, helped install the view that extinction was a natural and common occurrence, but also staunchly maintained that extinctions of individual species were always equally balanced by the appearance of new ones. In his famous Principles of Geology (1830–1833) he argued, on the one hand, that since “species are subject to incessant vicissitudes … it will follow that the successive destruction of species must now be part of the regular and constant order of nature,” while on the other that “the addition of any new species, or the permanent numerical increase of one previously established, must always be attended either by the local extermination or the numerical decrease of some other species” (Lyell 1830–1833, vol. 1: 141–142). In short, while Lyell envisioned an Earth that was subject to constant fluctuation and variation, he nonetheless held firm in the belief that “the successive extinction of terrestrial and aquatic species … [is] part of the economy of our system” (Lyell 1830–1833, vol. 2: 168).

It was this basic conception that informed Darwin’s own views on the role of extinction in natural selection and evolution. Throughout the Origin of Species, Darwin treated the relationship between extinction and speciation as a dynamic equilibrium, where extinction was understood simply as the failure of a species to adapt to its environment. Darwin believed that the total number of species had remained stable throughout Earth’s history, since the constant competition between organisms tended to average out between the winners and losers in the struggle for life. As he put it, “it inevitably follows, that as new species in the course of time are formed through natural selection, others will become rarer and rarer, and finally extinct” (Darwin 1859: 110), and that since a species is “maintained by having some advantage over those with which it comes into competition … the consequent extinction of less-favoured forms almost inevitably follows” (Darwin 1859: 320). In the Origin, Darwin envisioned the struggle for existence as a Malthusian zero-sum game that operated directly only on individuals, meaning that extinction would also tend to be a slow and gradual process, and that “the old notion of all the inhabitants of the earth having been swept away at successive periods by catastrophes, is very generally given up” (Darwin 1859: 317).

The Lyell/Darwin view of extinction as a gradual process that supported a stable equilibrium was, in general terms, the dominant view in Europe and America during the nineteenth century. It also both drew from and supported contemporary cultural and political beliefs about progress and European natural superiority that lent very little support to concerns about biological or cultural diversity. In Darwin’s scheme, extinction was the inevitable result of failure to compete in a “fair game”; extinct species were simply nature’s losers, and it was easy to transpose this perspective onto European political concerns. Even before Darwin, it was fairly common to invoke biological justifications for the consequences of European imperial expansion. According to Patrick Brantlinger, such expansion was often justified by the belief that the subjugation and extermination of so-called “savage” races – and their native floras and faunas – was the natural outcome of contact between superior and inferior civilizations, the latter of whom were “doomed” to inevitable extinction (Brantlinger 2003). It is hardly surprising that if extinction was seen to be an inevitable and natural occurrence, little concern was expressed for preserving cultural or biological diversity.

Lyell, for example, wrote in the Principles that “We must at once be convinced, that the annihilation of species has already been effected, and will continue to go on hereafter, in certain regions, in a still more rapid ratio, as the colonies of highly-civilized nations spread themselves over unoccupied lands” (Lyell 1830–1833, vol. 2: 156). This occasioned little regret, he argued, since “if we wield the sword of extermination as we advance, we have no reason to repine at the havoc committed, nor to fancy, with the Scottish poet, that ‘we violate the social union of nature,’” but rather merely should “reflect, that in thus obtaining possession of the earth by conquest … we exercise no exclusive prerogative. Every species which has spread itself from a small point over a wide area, must, in like manner, have marked its progress, by the diminution, or the entire extirpation, of some other” (Lyell 1830–1833, vol. 2: 156). Lyell emphasized that this explanation applied equally to “the extirpation of savage tribes of men by the advancing colony of some civilized nation.” While he did pause to express regret for this fact, he offered no apology, since, as he was quick to note, this was the natural and inevitable course of nature: “few future events are more certain than the speedy extermination of the Indians of North America and the savages of New Holland in the course of a few centuries, when these tribes will be remembered only in poetry and tradition” (Lyell 1830–1833, vol. 2: 175).

Such expressions were overwhelmingly common during the Victorian era. Darwin himself had remarked in his account of his voyage on the HMS Beagle that “wherever the European has trod, death seems to pursue the aboriginal,” and concluded that “the varieties of man seem to act on each other in the same way as different species of animals – the stronger always extirpating the weaker” (Darwin 1909: 459). Likewise, the physician and ethnographer James Cowles Prichard (1786–1848) wrote, in an 1840 essay in the Edinburgh Philosophical Journal titled “On the Extinction of the Human Races,” that “Wherever Europeans have settled, their arrival has been the harbinger of extermination to the native tribes … and it may happen that, in the course of another century, the aboriginal nations of most parts of the world will have ceased entirely to exist” (Prichard 1840: 168–170). And Darwin’s good friend and co-discoverer of natural selection, Alfred Russell Wallace (1823–1913), quite openly justified racial extinction as the result of natural selection applied to human beings. In an 1864 essay titled “The Origin of Human Races and the Antiquity of Man Deduced from the Theory of Natural Selection,” Wallace wrote that:

It is the same great law of “the preservation of favored races in the struggle for life,” which leads to the inevitable extinction of all those low and mentally undeveloped populations with which Europeans come in contact … [J]‌ust as the more favorable increase at the expense of the less favorable varieties in the animal and vegetable kingdoms, just as the weeds of Europe overrun North America and Australia, extinguishing native production by the inherent vigour of their organization, and by their greater capacity for existence and multiplication.

(Wallace 1864: clxiv–clxv) Darwin’s theory of evolution, then, merely reinforced an already well-established discourse of extinction that regarded the phenomenon to be part of the orderly balance of nature. It also showed remarkably little awareness of biological diversity as a phenomenon worthy of study or conservation – and why should it, if Darwin imagined that diversity was a property kept in intrinsic natural equilibrium? As he put it in the Origin:

Battle within battle must ever be recurring with varying success; and yet in the long-run the forces are so nicely balanced, that the face of nature remains uniform for long periods of time, though assuredly the merest trifle would often give victory to one organic being over another. Nevertheless so profound is our ignorance, and so high our presumption, that we marvel when we hear of the extinction of an organic being; and as we do not see the cause, we invoke cataclysms to desolate the world, or invent laws on the duration of the forms of life!

(Darwin 1859: 73)
While he understood the diversity of life to be in constant fluctuation, Darwin did not regard it to be affected or threatened by extinction: “Everyone has heard that when an American forest is cut down,” he remarked, “a very different vegetation springs up; but it has been observed that the trees now growing on the ancient Indian mounds, in the Southern United States, display the same beautiful diversity and proportion of kinds as in the surrounding virgin forests” (Darwin 1859: 112). In other words, nature’s inherent fecundity ensures that there will always be new forms standing by to replace the old ones, and that those new species will survive if they maintain a competitive advantage with their environments. He concluded ultimately that “Thus the appearance of new forms and the disappearance of old forms, both those naturally and those artificially produced, are bound together … we know that species have not gone on indefinitely increasing, at least during the later geological epochs, so that, looking to later times, we may believe that the production of new forms has caused the extinction of about the same number of old forms” (Darwin 1872: 296).

Ultimately, then, to the extent that Darwin recognized something like biological diversity in nature, he regarded it as an endlessly renewing resource. This attitude reflects both the older notion of “plentitude” in nature associated with Linnaeus and other theologically inspired naturalists, as well as Lyell’s interpretation of geological history as a dynamic equilibrium. What Darwin added was the regular cycle of extinction and speciation, which made Darwin’s view of nature considerably more transient than earlier conceptions of a static balance or economy. But beneath this constant change is a fundamental, underlying stability, provided thanks to nature’s capacity for endless self-generation of more diversity. The issue, then, isn’t whether Darwin recognized or thought natural variety was important – he certainly did – but rather whether he thought that diversity itself could be diminished by extinction, and whether the stability of nature could be threatened by a loss of diversity, which he did not. Competition and replacement were, for Darwin, the engine that drives the progressive improvement of the natural system, and which maintains the economy of nature. Far from seeing diversity as something to be conserved, he viewed it as essentially the fuel for that engine, the source of continued competition, selection, and extinction. The idea that nature exists in a harmonious, unchanging balance may have been upset, at the end of the eighteenth century, by authors such as Malthus and Cuvier, who suggested that competition and the specter of extinction are an inherent part of the natural order. But Darwin’s message was, essentially, that struggle and even extinction are positive forces – in the long view – thus soothing Victorian anxieties about their own impact on the world. The world may be subject to constant change, but faith in the ultimate constancy of nature was not shaken.

Extinction and biodiversity in the Age of Catastrophe

Viewed from an early twenty-first-century perspective, an extraordinary shift has taken place in the way we understand extinction and value biological diversity. It is now generally held that biodiversity is a precious “resource” for the health of our planet; mass extinctions are widely regarded to be events that have shaped evolutionary and ecological development of life at a number of points in the Earth’s history; and human diversity of all kinds – linguistic, ethnic, cultural – is considered a cherished asset. The transition from the nineteenth-century attitude to the one generally held today is an extremely complex story that can only be sketched in brief in this essay. Generally, however, the major factors responsible for this change encompass the narrowly scientific to the broadly cultural. In the first place, beginning in the 1950s, a new science of mass extinction developed – primarily in paleontology – which both conclusively established the reality of major mass extinctions in life’s past, as well as explicitly reoriented paleontology towards the quantitative analysis of patterns of biological diversity over time. Second, during roughly the same period, the discipline of ecology underwent a conceptual transformation that overturned earlier ideas about the intrinsic balance of nature. Ecosystems came to be seen as potentially much more vulnerable than had been previously suspected, and ecological diversity reconceptualized as a resource that could hedge against major environmental disruption (much as, slightly earlier, population geneticists advanced the notion that genetic diversity contributes to stability in populations). Third, awareness of the vulnerability of the environment was heightened by studies and popular accounts (such as Rachel Carson’s 1962 Silent Spring) that linked modernization with increased risk of extinction of plants, animals, and even humanity itself. And finally, the political and cultural climate changed quite dramatically, from Victorian optimism about limitless progress to a much more pessimistic tenor colored by experiences with world wars, political instability, nuclear proliferation, and rapid social change. This last feature contributed to a broadly foreboding atmosphere in much of the West, with threats of catastrophes of all kinds capturing the public (and scientific) imagination. These factors reached an apotheosis in the late 1970s and early 1980s, in what became the perfect storm of scientific and popular anxiety that produced the modern biodiversity consciousness.

Our current understanding of historical mass extinctions has roots in both immediate postwar paleontology and ecology. While Darwin’s explanation that most cases of extinction could be attributed to gradual competitive replacement appeared satisfactory to most subsequent observers, some paleontologists continued to be troubled by the more spectacular and apparently abrupt departures from the fossil record – the trilobites, for instance, or, especially, the dinosaurs (Packard 1886; Schuchert 1924). Nonetheless, for most of the scientific community, major events such as the extinction of the dinosaurs remained a mystery, and the subject of catastrophic mass extinctions was generally treated as acceptable for idle speculation, but not serious scientific study. This began to change only in the 1950s, and largely as the result of the efforts of a single paleontologist, the American invertebrate specialist Norman D. Newell. In a series of papers from the mid-1950s to the late 1960s, Newell helped to establish the legitimacy of mass extinction by taking a new approach: due to the rapid expansion of the marine invertebrate fossil record, thanks both to increased collecting efforts and new methods of fossil preparation, Newell realized he had an enormous quantity of data that could be mathematically analyzed to reveal broad evolutionary patterns (Sepkoski 2012: ch. 2). The results of these investigations were graphs that clearly showed major mass events as distinctive spikes that stood out against the background of “normal” extinction. Despite skepticism from many colleagues, Newell pushed forward with his work, and in 1967 produced a definitive study of mass extinction that concluded that “modern paleontology must incorporate certain aspects of both catastrophism and uniformitarianism while rejecting others” (Newell 1967: 64).

While Newell declined to characterize these mass extinctions as true “catastrophes” (in the sense of a sudden event – he rather favored gradual changes in sea level as the culprit), his work set the stage for further study by legitimating the topic. Importantly, his research also helped draw a closer connection between the study of mass extinctions and the study of diversification. In Newell’s quantitative approach (which was refined over the next several decades by students and admirers), extinctions were detected as major drops in standing biological diversity. Absent other kinds of physical evidence about their causes, paleontologists began to see extinctions as, literally, spikes (or troughs) in diversity graphs. As biology increasingly turned to computers and a “data-driven” approach, such statistical estimates of diversity and extinction became valuable tools both for historical studies and for modern conservation efforts. Ultimately, mass extinction came to be defined as a statistical aberration in diversity data.

The study of biological diversification and extinction at this time was also significantly influenced by new ecological approaches, many of which originated in the circle of the Yale ecologist G. Evelyn Hutchinson. Some of this impact was methodological: Hutchinson and his students (especially Robert A. MacArthur) developed heuristic mathematical models for studying phenomena such as species abundance, migration, and population limits as fluctuations in ecological diversity (Kingsland 1985, Dritschilo 2008). Some of these techniques, such as MacArthur and E. O. Wilson’s “species-area effect” and their theory of island biogeography had a major impact on paleontology by providing models that could be applied to diversification and extinction over geological time (Sepkoski 2012: ch. 4). But Hutchinson himself also helped spark a new conceptual orientation towards ecological diversity by closely identifying niche diversity with ecological stability. As he put it in a landmark 1959 paper “Homage to Santa Rosalia; or Why Are There So Many Kinds of Animals?,” “Modern ecological theory appears to answer our initial question at least partially by saying that there is a great diversity of organisms because communities of many diversified organisms are better able to persist than are communities of fewer less diversified organisms” (Hutchinson 1959: 150). In other words, diverse communities are more resistant to unexpected environmental change because they have a greater number of “options” to cope with that change.

This idea essentially reflects the wisdom of ‘‘not putting all of one’s eggs in one basket,’’ and follows closely the logic of the population geneticist Theodosius Dobzhansky, who in 1937 had argued that high genetic diversity in a population constitutes “a store of concealed, potential, variability,” and warned that “A species perfectly adapted to its environment may be completely destroyed by a change in the latter [its environment] if no hereditary variability is available in the hour of need” (Dobzhansky 1937: 127). This ecological/genetic argument for the importance of diversity as a “storehouse” against unforeseen change is, I argue, a vital component of modern biodiversity discourse. It emerged largely in the post-World War II context, and influenced both emerging environmental movements as well as debates about race and cultural diversity. This moment also reveals quite clearly how scientific debates became entwined with cultural and political problems around diversity. For Dobzhansky and his students (especially the geneticist Richard Lewontin), studies of genetic variability and diversity became the basis for political stances against racism and in favor of protecting cultural diversity (Dobzhansky 1962, Lewontin et al. 1984). For Hutchinson, it was a call to arms that would reverberate across the decades to the modern biodiversity conservation movement. At the end of “Homage to Santa Rosalia” Hutchinson described the “indiscriminate” reduction of diversity caused by human actions, and opined that “we may hope for a limited reversal of this process when man becomes aware of the value of diversity no less in an economic than in an esthetic and scientific sense” (Hutchinson 1959: 156).

The political and cultural sources of change in the postwar period are harder to quantify, though seemingly ubiquitous. The ways in which anxieties about nuclear annihilation seeped into popular consciousness in the West in the 1950s and beyond have been well documented, producing, in the words of historian Spencer R. Weart, “a world of fear, suspicion, and almost inevitable catastrophe” (Weart 1988: 115). Above all, threat of nuclear Armageddon signaled a shift in thinking about human progress and permanence towards a much darker and more pessimistic direction. The images of the Trinity test site or the mushroom clouds over Hiroshima and Nagasaki also focused attention on the spectacular, or catastrophic. This was reflected in popular culture (movies such as Planet of the Apes and On the Beach) that dramatized the onset or aftermath of nuclear conflagration; in politics, where events such as the Cuban Missile Crisis paralyzed the American public; and in emerging environmental awareness, where works such as Rachel Carson’s Silent Spring warned that “Along with the possibility of the extinction of mankind by nuclear war, the central problem of our age has therefore become the contamination of man’s total environment” (Carson 1962: 8). As Weart broadly summarizes,

Nuclear weapons gave the twentieth century’s nihilism a dismal solution. Immediately upon hearing the news from Hiroshima, sensitive thinkers had realized that doomsday – an idea that until then had seemed like a religious or science-fiction myth, something outside worldly time – would become as real a part of the possible future as tomorrow’s breakfast.

(Weart 1988: 392) This general climate of anxiety also contributed to public and scientific interest in mass extinctions. While it was pilloried by virtually all experts, Immanuel Velikovsky’s account of celestial catastrophe Worlds in Collision (1950) was a worldwide bestseller and lodged itself in the popular imagination for decades. Although it may have done more harm than good to the scientific acceptance of catastrophic mass extinctions (by further associating “catastrophism” with pseudo-science), it has recently been described by a historian as “one of postwar America’s most culturally significant works about the natural world” (Gordin 2012: 135). Even as he dismissed it as “a pathetic, ominous, and superstitious piece of work,” New Yorker reviewer Alfred Kazin nonetheless acknowledged that Worlds in Collision “fits only too well into the intellectual melodrama of this period” (Kazin 1950: 103). That “melodrama” had, by the early 1970s, joined a nearly omnipresent threat of political breakdown and nuclear war with a host of additional existential threats and morbid fascinations: catastrophic environmental pollution, dire warnings of an immanent population explosion, political radicalism and terrorism in Europe and the US, and daily scenes of body bags being loaded onto planes in Southeast Asia. For many observers, the end of the world did indeed appear nigh.

When, in 1980, the father-and-son team of Luis and Walter Alvarez published a paper claiming to have discovered evidence of a massive bolide impact some 65 million years ago that triggered a worldwide catastrophe, they did more than just provide a potential answer to a longstanding scientific mystery (Alvarez et al. 1980). The particular scenario they envisioned – a cataclysmic impact, followed by worldwide firestorms, deadly acid rains, months of near-total darkness, a massive greenhouse effect that lasted for thousands of years, and extinction of the dinosaurs – spoke directly to the public’s consciousness of our own species’ tenuous grip on the planet. Indeed, the very scenario adopted for the Alvarez impact hypothesis was borrowed by the astronomer Carl Sagan and others to provide the basis for models of the so-called nuclear winter that would follow a global thermonuclear exchange (Badash 2009). The impact of the theory on popular consciousness is probably best exemplified in a contemporary newspaper column written in 1984, whose author, Ellen Goodman, asked “I wonder whether every era gets the dinosaur story it deserves,” noting that “the scientists of the 19th century – a time full of belief in progress – saw evolution as part of the planet’s plan of self-improvement … Those who lived in a competitive economy valued the ‘natural’ competition of species. The best man won.” But, she continued, “surely we are now more sensitive to cosmic catastrophe, to accident,” adding “in that sense, the latest dinosaur theory fits us uncomfortably well. ‘Our’ dinosaurs died together in some meteoric winter, the victims of a global catastrophe. As humans, we fear a similar shared fate.” However, as Goodman observed in closing her column, “the difference is that their world was hit by a giant asteroid while we – the large-brained, adaptable creatures who inherited the earth – may produce our own extinction” (Goodman 1984).

Along with the spectacular publicity the Alvarez theory attracted, the extinction research initiated by Newell reached maturity during the late 1970s and early 1980s. Building on the equilibrial models of ecological theorists like MacArthur and Wilson, a small group of paleontologists – including David M. Raup, J. John Sepkoski, Jr., and David Jablonski – began producing more refined quantitative studies of the history of diversification and extinction over the past 500 million years. What this research showed was that while there has been (contrary to Darwin’s expectation) a general trend towards increased diversity over the history of life, the pattern of diversification has been perturbed a number of times in what paleontologists determined were major mass extinctions (Sepkoski 1984). Those extinctions – Raup and Sepkoski had detected five such major events – had a profound impact on subsequent evolution by producing massive evolutionary “bottlenecks” (steep reductions in remaining genetic diversity) and also by opening up new ecological space – and creating new ecological conditions – for natural selection to work in (Raup and Sepkoski 1982). One implication of this pattern of extinction and diversification was that while the taxonomic groups that survived mass extinctions eventually did recover and diversify, the total amount of what Stephen Jay Gould has called “disparity” (i.e. major morphological or genetic differentiation between higher taxa) was permanently reduced. In other words, what are left after mass extinctions are a greater number of species and genera (and fewer families and orders) that are more similar to one another. Another implication explored by Raup and Jablonski is that in the aftermath of catastrophic mass extinctions “normal” evolutionary rules do not apply: while normal “background” extinction is probably as gradual and selective as Darwin had envisioned, mass extinctions may target taxonomic groups that had been perfectly well-adapted to previous conditions and who become extinct through no “fault” of their own (Jablonski 1986). As Raup put it in a popular book some years later, many cases of extinction may simply be the result of “bad luck” (Raup 1991).

This was the setting out of which the biodiversity conservation movement emerged. While conservation biologists and ecologists had been warning for years that human activity was putting many species at risk (Myers 1979), paleontological study of extinction and diversification provided a quantitative metric for assessing the present crisis and the future consequences. As Wilson put it in his 1992 The Diversity of Life, “the laws of biological diversity are written in the equations of speciation and extinction” (Wilson 1992: 220). In fact, Wilson and other biodiversity activists immediately began using Raup’s calculation of the normal or “background” rate of extinction for the past 500 million years – two to three species per year, in Raup’s estimate – as the figure against which to compare current rates of species loss. The direct source, then, for considering the modern biodiversity crisis to be a potential “mass extinction” are paleontological studies of mass extinctions and diversification from the 1970s and 1980s. It is in those terms that the crisis is sometimes called a “sixth extinction” (number five being the one that eliminated the dinosaurs), and predictions about the evolutionary, ecological, and environmental consequences of a current mass extinction are explicitly informed by paleontology (Leakey and Lewin 1995).

While biodiversity activists like Wilson certainly actively sought out the participation of paleontologists – Raup was a featured presenter at the first BioDiversity conference in 1986 – paleontologists have also actively sought to contribute their expertise to the discussion. Raup warned at the initial meeting that “without consideration of the time perspective available from the geological record, a full evaluation of the contemporary extinction problem may prove as difficult as would be the case … if an epidemiologist were to treat an infectious disease without medical records” (Raup 1988: 57). This statement echoed Wilson’s own contribution, which compared the current crisis to “the great natural catastrophes at the end of the Paleozoic and Mesozoic eras,” cautioning that “the modern episode exceeds anything in the geologic past” (Wilson 1988b: 11–12). Many of the paleontologists most directly responsible for uncovering the ecological dynamics of mass extinctions would subsequently comment on the contemporary crisis as well. For example, Sepkoski argued in 1997 that “it may indeed be possible that we are on the brink of the greatest of all mass extinctions,” and encouraged activism among his colleagues by noting that “we are the only scientists who have ever seen biodiversity crises to their end … and have some idea of what happens in their aftermath” (Sepkoski 1997: 536). Likewise, Michael Benton has concluded that “extinction events in the fossil record … can give indications of what might, or might not, happen in the future,” and pointed out that “comparison of present crises with documented ancient examples at least allows scientists and policy makers to work with real facts and figures” (Benton 2003: 8 and 16). As Jablonski has put it, “in order to understand the dynamics of biodiversity … we need to understand extinctions and their complex aftermath” (Jablonski 2004: 174), reminding us that “whatever the exact magnitude of present-day diversity losses, rebounds in the fossil record suggest that they will not be recouped in the next thousand years” (Jablonski 1991: 755).


I have tried to emphasize two related points in this chapter. First, valuations of biodiversity are closely tied to biological understanding of extinction. Much of the urgency surrounding discussions of the current state of biodiversity are dependent on a particular conception of mass extinction that has emerged only in the past few decades. Second, these values have shifted over time, partly due to changing biological views of extinction, and in part because of broader cultural transformations. It is undoubtedly the case that science has an important role in shaping public perceptions of the natural world, but scientists are also participants in their cultures and to some degree are influenced by broader social and political values. Victorian naturalists like Lyell and Darwin – though politically liberal for their day – shared the same easy optimism about limitless future progress that their contemporary statesmen and captains of industry held. They would have been as unlikely to credit the possibility that humanity might extinguish itself in a few short generations as they would to acknowledge that the spread of European culture might have a harmful effect. The evidence of mass extinction had already been presented – thanks to Cuvier – but it was rejected in favor of another, equally plausible explanation (for its time) that fit more comfortably with middle-class European values.

Likewise, mid-twentieth-century biologists and paleontologists were quite explicitly conditioned by the same Cold War climate of fear and anxiety that affected their non-scientist contemporaries. Paleontologists like Raup and Sepkoski did, to be sure, have access to data and tools (such as computers) that their predecessors lacked. But even so, they faced an uphill battle to convince their colleagues that major mass extinctions had taken place, and the ultimate acceptance of their ideas was attributable, at least in part, to living in a society where the threat of catastrophe had become culturally ingrained. It is certainly the case that the modern biodiversity movement has capitalized on the convergence of science and culture around extinction, as evidenced by the fact that the notion that we are living through a potential “sixth extinction” has earned widespread cultural currency. This is not to say that without the input of paleontologists there would be no biodiversity movement, but rather that the particular discourse that exists around biodiversity conservation has been shaped very directly by recent reconceptualizations of extinction.

Ultimately, this suggests that even some of our culture’s deepest values and assumptions – the idea of the “balance of nature,” for example – are subject to revision. Little more than a hundred years ago most biologists would have described the natural world as an endlessly renewing resource incapable of being destabilized by mere human actions. Today, we think quite otherwise. In response to “some apologists for development [who] have argued that extinction at any scale … poses no biological worry but, on the contrary, must be viewed as part of an inevitable natural order,” Stephen Jay Gould has commented that “capacity for recovery at geological scales has no bearing whatever upon the meaning of extinction today” (Gould 1990). Nor does Wilson believe that current data on biodiversity loss should comfort “anyone who believes that what Homo sapiens destroys, Nature will redeem,” at least “within any length of time that has meaning for contemporary humanity” (Wilson 1992: 31). Diversity – whether biological or cultural – is now seen as a resource that must be actively preserved, since once lost it is not easily recovered. On geological scales, the Earth may indeed be self-sustaining, but that may come as little comfort to us human beings. After all, as Gould reminds us, “our planet will take good care of itself and let time clear the impact of any human malfeasance” (Gould 1990).


A longstanding historical chestnut holds that Cuvier’s theory of catastrophic upheaval was aligned with a biblical chronology of the Earth. As Martin Rudwick has shown, this interpretation was promoted mostly by nineteenth-century British geologists who mixed Cuvier’s decidedly naturalistic theory with their own scriptural geology (Rudwick 2005).


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