Meeting the United Nations’ sustainable development goals, mitigating and adapting to climate change, preventing biodiversity loss and addressing the myriad other environmental issues confronting us this century will require scholars, policy makers, activists and citizens to jointly tackle a series of social, political, economic and environmental challenges. To succeed, these efforts must be informed by social theories capable of conceptualizing the interactions between social structures, human agency and biophysical environments.Environmental sociologists have grappled with two questions at the heart of these efforts: First, what accounts for the historic inability of the social sciences to integrate the biophysical environment into social theory? And, second, how can such integration be achieved both in principle and in practice? These questions can be answered by tracing the parallels between the Darwinian revolution--which faced a similar challenge of theoretically integrating the environment--and recent shifts in our way of looking at the environment and sociology. These parallels suggest that the social sciences are undergoing a second Darwinian revolution.[1] Understanding this intellectual convergence is the key to constructing new theories of cultural evolution to better inform the decisions we make about the environment.Ernst Mayr argues that the first Darwinian revolution was “perhaps the most fundamental of all intellectual revolutions.”[2] Moreover, in this case, the term revolution is a misnomer. The publication of The Origin of the Species marked the midpoint of a complex process spanning 250 years and requiring the rejection of six assumptions. Analogues to each of these shifts can be found in the social sciences.Revising the Age of the EarthDarwin realized that establishing the fact of evolution and his specific mechanism of natural selection required a timescale exceeding that provided by conservative biblical exegesis. However, by 1859 accumulating evidence had eliminated the age of the earth as a significant objection to his theory. Nevertheless, with respect to time, Darwin faced a greater challenge--how to persuade fellow naturalists to replace a static with a dynamic worldview. Here Darwin confronted not only religious conservatism but Plato and Aristotle’s conviction that reliable knowledge can only be obtained by searching for the invariances beneath the flux of reality. This belief persisted in pre-Darwinian theories of progressive evolution, such as Lamarck’s, which treated time-and-place events--including the effects of environmental forces--as surface phenomena which could cause deviations from but not fundamentally alter the postulated teleological trend toward complexity. Darwin overcame the resulting false dichotomy between science and history by abandoning the search for invariances in favor of a detailed analysis of time-and-place events. His historical and probabilistic theory was a radical departure from Newton’s ideal of timeless, universal laws, leading the astronomer John F.W. Herschel to deride natural selection as “the law of higgledy-piggledy.”[3]The social sciences are undergoing a parallel shift from a teleological to an eventful temporality.[4] Lamarck’s theory of biological progress is directly analogous to the idea of social development or progress. The latter originated with Aristotle’s Politics, was assimilated into Christianity by St. Augustine, re-secularized during the Enlightenment, elaborated by Spencer, Tylor, Morgan, Durkheim and Marx in the 19th-century and persists today in the guise of assorted theories of modernization--e.g., ecological modernization theory.[5] These theories share Plato and Aristotle’s commitment to identifying the invariances beneath the flux of history and a concomitant discounting of time-and-place events. In the past half century, ecological anthropologists from Julian Steward to Stephen Lansing have demonstrated that environmental variations in space and time are not merely surface phenomena; these events are the fundamental determinants of the multiple, context-dependent paths taken by social evolution. An identical shift toward an “event ecology” is occurring in sociology.[6] For instance, environmental sociologists have argued that a detailed understanding time-and-place events is critical to reducing vulnerabilities to climate change and other natural hazards.[7] Rudel, likewise, has criticized recent work on deforestation for its “disembodied, ahistorical quality,” and its failure to identify “the agents of change and the timing of transformative events.”[8]Refuting a Steady-State World and CatastrophismTwo schools of geology emerged prior to 1859. Uniformitarians, like Charles Lyell, were liberal deists who rejected any role for religion in science. Lyell envisioned the earth as a balanced, homeostatic system. He insisted that the type and intensity of geological forces were relatively constant. Lyell also agreed with James Hutton that geology revealed “no vestige of a beginning--no prospect of an end.”[9] In contrast, Catastrophists were conservative theists and reluctant to extend the biblical timescale. Cuvier, who founded this school, saw the earth as inherently dynamic. He treated each geological stratum as an integrated system and argued that the discontinuities between strata implied the lawlike operation of forces of greater magnitude than any observed at the time. However, other catastrophists translated Cuvier’s caution into a belief in recurrent supernatural cataclysms followed by the miraculous recreation of progressively more advanced life-forms. Evidence soon compelled uniformitarians to accept more powerful geological forces and catastrophists to abandon large-scale supernatural cataclysms. Darwin eventually combined the uniformitarians’ commitment to natural law with the catastrophists’ belief in a dynamic--though not progressive--world.The sociological equivalent to the uniformitarian/catastrophist dichotomy is the order/conflict dichotomy. Emile Durkheim’s conservative image of society as a tightly integrated, homeostatic system provides a counterpart to Lyell’s uniformitarianism, while Marx’s portrayal of capitalist societies as riven with class conflicts and economic crises, culminating in revolution, is an exemplar of social catastrophism. These overly systematic images of earth and society are derived from Aristotle’s essentialism (see below). However, as in geology, accumulating evidence has eroded the order/conflict dichotomy. Ecological anthropologists and environmental sociologists have criticized Durkheim’s image of self-equilibrating social systems for obscuring the causes of resource depletion and environmental degradation. And, they have embraced the dynamic, non-equilibrium assumptions of the new ecology to explore the adaptation of social units below the level of whole societies. The Marxian revolutionary metanarrative has undergone a parallel decomposition as neo-Marxian political economists have been obliged, like geological catastrophists, to acknowledge an increasing number and diminishing scale of “revolutionary” events. Indeed, the political economy perspective is giving way to a new political ecology which has “increasingly turned attention to local-level studies…of power, knowledge and practice” while simultaneously acknowledging an independent causal role for the environment.[10]Refuting an Automatic Upward EvolutionThe concept of an automatic upward evolution emerged from the temporalization of Plato’s Chain of Being. Plato’s realm of Ideas began as a static hierarchy of complexity, with the Idea of the Good--Plato’s God --at the apex. For Plato, “The essence of ‘good’…lay in self-containment, freedom from all dependence upon that which is external.” Plato’s equation of the Good with self-sufficiency is an unexplored root of human exemptionalism. Since a lack of envy was also constitutive of the Good, Plato’s God could not begrudge existence to less perfect beings. The resulting principle of plenitude required the actualization of Plato’s entire hierarchy, translating “The concept of Self-Sufficing Perfection…into the concept of a Self-Transcending Fecundity.”[11] In the 18th century, the static Chain collapsed. The dissonance between Plato’s God, who acted from necessity, and a Christian God with free will could no longer be suppressed. Likewise, the principle of plenitude implied that the existing world was the best of possible worlds. In Candide, Voltaire ridiculed such Panglossian optimism for precluding any hope of alleviating human suffering. The static Chain also succumbed to disconfirming paleontological evidence. Lamarck, Geoffroy Saint-Hilaire, and Robert Chambers tried to resolve these evidential difficulties by reinterpreting the Scala Natura as an historical process. However, discrepancies between this temporalized Chain and the fossil record mounted. Ultimately, theories of progressive evolution failed to explain both observed patterns of temporal and spatial diversity and the origins and dynamics of adaptation. By redefining evolution as a mechanism--natural selection--rather than a direction, Darwin explained both phenomena as a consequence of descent with modification.Theories of social development or progress have demonstrated a corresponding inability to account for structural diversity and environmental adaptation. They have experienced additional difficulties theorizing human agency. Like the temporalized Chain of Being, developmental theories are collapsing under the weight of their own political and empirical deficiencies. As a political frame, the idea of progress has been criticized for legitimating environmentally destructive technologies and practices. Both the collectivization of Soviet agriculture and the green revolution illustrate the social and environmental tragedies that result when context-independent ideals are translated into public policy. Theories of progress have also been denounced for promoting a Panglossian belief that development is inherently beneficial, while marginalizing people and projects that challenge the dominant discourse. And they have been undermined empirically. Attempts to explain “deviations” from hypothesized natural trends by elaborating theories of obstacles and interfering forces have consistently failed.[12] Finally, theorists of development have not explained adaptation. Like Lamarck, they see adaptation as a universal necessity but not a serious problem because progress entails adaptive upgrading which ensures adjustment to and/or independence from the environment. In the face of climate change and other global threats, such progressive human exemptionalism is no longer tenable. And, as in biology, the above failures are prompting a shift from linear grand narratives to local multilinear histories.Replacing Essentialism and Nominalism with Population ThinkingDarwin’s rejection of essentialism and nominalism in favor of population thinking is the cornerstone of the Darwinian revolution. Essentialism includes Plato’s ideas and Aristotle’s Natural State Model (NSM). The latter, materialist version of essentialism, provided the foundation for modern science. Application of the NSM involves: (1) defining categories so that every member shares a unique set of common properties or functional relationships, (2) identifying the natural state or path of change characteristic of members of that category, and (3) distinguishing natural tendencies from deviations caused by obstacles or interfering forces.[13] The NSM succeeded in chemistry and physics because researchers were able to systematically theorize deviations. However, in historical sciences like biology, the sheer number of secondary forces and the resulting complexity of events undermined this metatheoretical strategy. As noted, the NSM likewise proved incapable of explaining adaptation. The NSM is a frame-invariant approach to theory construction; its goal is to analytically strip away the effects of external forces to uncover context-independent patterns. Adaptation is an inherently contextual phenomena and cannot be explained in this manner.The breakdown of essentialism in biology was facilitated by the reemergence of nominalism, a medieval metatheory, which holds that “All groupings, all classes, are artifacts of the human mind” and, thus, only individuals are “real.”[14] Nominalism undermined the essentialist conviction that species are discrete and immutable and provided Darwin with an alternative theoretical starting point. Rather than common properties or functional relationships, Darwin took the individual differences, dismissed by essentialists and highlighted by nominalists, and reconceptualized evolution as a continuous process of interaction between the inherited variability within a population and its environment. The environment filters the less from the more fit individuals, increasing the latter’s prevalence in future generations. Rather than seeking “a reality that underlies diversity” populationists attempt to theorize “a reality sustained by diversity.”[15] Population thinking represents a frame-relative approach to theory construction; it looks for patterns in the relationships between diversity and context.Recent developments in environmental sociology parallel these shifts. Although populational theories are still marginal in the field, the increasing recognition of essentialism’s limitations is laying the groundwork for their wider acceptance. In recent decades, ecological anthropologists and environmental sociologists have implicitly rejected essentialism by shifting from a teleological to an eventful temporality and by rejecting the order/conflict dichotomy and linear grand narratives. The number and complexity of so-called interfering forces has, likewise, undermined essentialists’ attempts to explain structural diversity and rendered attempts to incorporate human agency intractable. And, as in biology, it has proven impossible to theorize the inherently contextual process of social adaptation using a frame-invariant metatheory.The recent emergence of radical or nominalist forms of constructionism has accelerated the collapse of essentialism in the social sciences. As in the Darwinian revolution, constructionism has destabilized essentialism by reconceptualizing social categories as arbitrary divisions of continua of individual differences. Treating categories as cultural conventions contested by actors situated within particular historical contexts has allowed constructionists to better address question of human agency and culture.[16] However, they have been criticized for subsuming nature into history and for failing to conceptualize the environment as an independent causal force. Moreover, constructionists lack a conceptual mechanism linking social structures, human agency and biophysical environments. They are still struggling to explain “how narrative and text matter and how categories and the apprehension of knowledge is linked to ecological change.”[17]Despite its deficiencies, radical constructionism is facilitating the emergence of populational theories of change in environmental sociology by undermining essentialism and highlighting diversity. For instance, McLaughlin, building on Dietz and Burn’s earlier work,[18] is using the concept of a socially constructed adaptive landscape to integrate organizational sociologists’ insights into structure-environment interaction, constructionists’ attention to agency, language, culture, and values, and political ecologists’ concerns with power, inequality, and processes of marginalization. The concept of a socially constructed adaptive landscape represents a negotiated and contested fitness terrain that describes the relationship between a population of social structures--e.g., social roles, routines, or organizations--and specific biophysical, social, economic, political and discursive environments. It graphically represents the probability of a social form persisting or propagating in a given environment relative to forms with different characteristics. Individual and corporate actors adapt to this terrain through homeostatic, developmental, calculative, and populational mechanisms. They simultaneously deploy human agency to actively alter the landscape by using collective action frames to mobilize resources and create or exploit political opportunities in order to legitimate or delegitimate social structures and their associated technologies at various levels of analysis. Legitimation (delegitimation) involves the creation (collapse) of a new peak or fold on the landscape. It also requires the construction (deconstruction) of social boundaries. The focus on boundary dynamics represents a moderate form of constructionism that, following biology, avoids the essentialist/ nominalist dichotomy by conceptualizing categories in historical yet realist terms.Rejecting CreationismDarwin’s rejection of creationism culminated a trend, beginning with Descartes’ mechanical philosophy and reinforced by Enlightenment materialism, toward a temporal and causal estrangement of the deity. It also drove a wedge between the natural and the good. Judeo-Christian creation myths assumed that the moral order was grounded in the natural order. The Greeks likewise maintained that “The good for any being…lies in the realization of its specific ‘nature.’”[19] Darwin’s rejection of creationism and essentialism undermined this identity, because “Without fixed natural categories, without a fixed boundary between nature and culture, without a fixed ‘human nature,’ and without any overall direction in the life process, it is impossible to make nature into a source of ethical and political prescriptions.”[20]A corresponding rejection of ethical foundationalism is occurring in the social sciences. Classical theorists of progress, such as Marx and Durkheim, privileged certain historical trajectories as natural and therefore good. As Gilbert Rist notes, religiosity did not disappear with the Enlightenment; it simply “migrated elsewhere.” Indeed, development became our “modern religion.” It short-circuited political debate by placing certain values “beyond dispute.”[21] The technological domination of nature is a central tenet of this religion. Environmental sociologists have challenged the “naturalness” of this belief system and its associated environmental externalities by replacing linear grand narratives with local multilinear histories. This shift avoids the normative foreclosures associated with conservative and liberal ideologies of development that have been used to render “alternatives invisible and unthinkable” and thus deny agency to local groups fighting to protect their environments.[22] In contrast, multilinear theories of cultural evolution facilitate the theoretical incorporation and political deployment of agency. They are also consistent with emerging experimentalist approaches to environmental governance which seek to open rather than foreclose debate by putting neither the means nor the ends of environmental policy beyond dispute.[23]Abolishing AnthropocentrismThe Judeo-Christian and Greek traditions accorded humans a special place within nature. By rejecting creationism and the Chain of Being, Darwin completed the process of decentering humanity begun by Copernicus. While Copernicus displaced humans from the spatial focal point of medieval cosmology, Darwin repositioned them temporally. For Darwin, humans were neither part of creation nor the end point of history. Instead, he saw humanity as one small and transient branch on an indefinitely diverging evolutionary tree.The repudiation of anthropocentrism and the presumed exemption of humans from environmental limits is a central tenet of environmental sociology.[24] The ongoing rejection of frame-invariant, linear grand narratives, the elaboration of biocentric ethics as a counterpoise to the Greek ideal of self-sufficiency, the rise of animal studies, and feminist critiques of the patriarchal insistence on “man’s” domination of nature all reflect environmental sociologists’ commitment to purging the discipline of anthropocentric influences.ConclusionThe above comparisons substantiate Loren Eiseley’s claim that “almost every mistake and folly which was perpetuated in the creation of a satisfactory theory of organic evolution was duplicated or had its analogue in the social field.”[25] Such parallels are interesting solely in terms of the comparative history, philosophy and sociology of science. However, they can also resolve the current impasse in environmental sociology by demonstrating that Plato’s principle of self-sufficiency and Aristotle’s NSM are the root causes of the social sciences’ historic inability to theoretically integrate the environment. The persistence of a teleological temporality, the order/conflict dichotomy, linear grand narratives, foundationalism, and anthropocentrism have reinforced these anti-environmental commitments. Their ongoing rejection constitutes a second Darwinian revolution.A fuller appreciation of the metatheoretical parallels between the biological and social sciences can also clarify how the biophysical environment can be integrated into social theory both in principle and in practice. Social scientists should follow Darwin’s lead by rejecting both essentialism and nominalism in favor of population thinking. By treating social change as a frame-relative mechanism rather than a frame-invariant direction, population thinking can facilitate the construction of theories of societal-environmental interaction that “steer a narrow road between randomness and teleology.”[26] Although still a minority position, the advent of evolutionary theories in environmental sociology points in this direction, as does the emergence of comparable populational theories in anthropology, economics, history, linguistics, philosophy, political science and organizational sociology. Together these theories can provide a stronger framework for theorizing the transition to a more sustainable society.References[1] McLaughlin, P. (2012). The second Darwinian revolution: Steps toward a new evolutionary environmental sociology. Nature and Culture, 7(3), 231–258.[2] Mayr, E. (1972). The nature of the Darwinian revolution. Science, 176, 981-89.[3] Hull, D. L. (1973). 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