{
  "1": {
    "summary": "One science of feedback, control and communication for machines, organisms and societies.",
    "description": "Norbert Wiener, Arturo Rosenblueth and Julian Bigelow argued in “Behavior, Purpose and Teleology” (1943) that purposeful behaviour, in animals and anti-aircraft predictors alike, is feedback control. Wiener’s *Cybernetics* (1948) named the field, and the Macy conferences (1946–1953) brought Warren McCulloch, Gregory Bateson, Claude Shannon and John von Neumann into it. W. Ross Ashby built the homeostat (1948) and stated the law of requisite variety in *An Introduction to Cybernetics* (1956), and Stafford Beer applied cybernetics to management. By the 1970s the programme had dispersed into cognitive science and artificial intelligence, control engineering and second-order cybernetics."
  },
  "2": {
    "summary": "The mathematics of using feedback to hold a machine on target, and of proving that it stays stable.",
    "description": "James Clerk Maxwell’s “On Governors” (1868) treated the steam-engine regulator as a stability problem in differential equations. Between the wars Bell Labs engineers added frequency-domain tools: Harold Black’s negative-feedback amplifier (1927), Harry Nyquist’s stability criterion (1932) and Hendrik Bode’s plots. Rudolf Kálmán’s state-space methods and filter (1960) recast the field for computers and spaceflight. Control theory is still a core engineering discipline; cybernetics and system dynamics took their mathematics of feedback from it, and systems biology its account of robustness."
  },
  "3": {
    "summary": "Information measured as entropy, and the limits on how much of it a noisy channel can carry.",
    "description": "Claude Shannon’s “A Mathematical Theory of Communication” (1948) defined information as a quantity, entropy in bits, and proved that every channel has a capacity below which transmission can be made as reliable as desired. Shannon noted that his entropy has the form of Ludwig Boltzmann’s and Josiah Willard Gibbs’s entropy in statistical mechanics, and Edwin Jaynes later reversed the borrowing, rebuilding statistical mechanics as inference. Andrey Kolmogorov added a complexity measure for individual objects. Coding and telecommunications rest on the discipline, cognitive psychology measured the span of memory in its bits (Miller 1956), and complexity science takes its measures of order, surprise and mutual information from it."
  },
  "4": {
    "summary": "Organisms, machines and societies as open systems governed by common laws, to be studied by one science.",
    "description": "Ludwig von Bertalanffy, a Vienna-trained biologist, argued from the 1930s that organisms are open systems exchanging matter and energy with their surroundings, and that the same principles – wholeness, hierarchy, equifinality – recur across disciplines; he saw his organismic biology of the 1920s paralleled in Alfred North Whitehead. His programme for a general theory of systems, written in 1945, was first printed in 1949 as “Zu einer allgemeinen Systemlehre”. With Kenneth Boulding, Anatol Rapoport and Ralph Gerard he founded in 1954 the society that became the Society for General Systems Research, now the International Society for the Systems Sciences, and Boulding’s “General Systems Theory – The Skeleton of Science” (1956) took cybernetics in as the third level of its hierarchy of systems. Systems thinking, systems ecology and Niklas Luhmann’s sociology took up its ideas, and Mihajlo Mesarović’s symposium *Systems Theory and Biology* (1968) carried them towards what became systems biology."
  },
  "5": {
    "summary": "Practical systems methods for messy human problems, from soft systems to learning organisations.",
    "description": "C. West Churchman’s *The Systems Approach* (1968) took the systems idea out of operations research and into questions of purpose and values. Peter Checkland’s soft systems methodology (*Systems Thinking, Systems Practice*, 1981) and Russell Ackoff’s work on messes treated problems as negotiated between stakeholders. Donella Meadows, from Jay Forrester’s MIT group, was teaching system dynamics without the computer by 1980 (“Whole Earth Models and Systems”, 1982), and her leverage points made it a tool for intervention; Peter Senge’s *The Fifth Discipline* (1990) carried its feedback loops, as causal-loop diagrams, into a management bestseller. The programme continues in critical systems thinking and in sustainability practice."
  },
  "6": {
    "summary": "Stocks, flows and delayed feedback, simulated on a computer to show why policies misfire.",
    "description": "Jay Forrester, a servomechanism engineer at MIT, simulated by hand the hiring and inventory loops behind the employment cycles at General Electric’s Kentucky appliance plants in the mid-1950s, and called the result industrial dynamics (*Industrial Dynamics*, 1961). *Urban Dynamics* (1969) and *World Dynamics* (1971) scaled the method to cities and the planet. *The Limits to Growth* (1972), written by Donella Meadows, Dennis Meadows, Jørgen Randers and William Behrens for a project Dennis Meadows directed, made the World3 model a public argument. John Sterman’s *Business Dynamics* (2000) is the standard text. Climate simulators such as En-ROADS use the method today."
  },
  "7": {
    "summary": "Emergence, self-organisation and scaling across physics, biology and economics as one field, built around the Santa Fe Institute.",
    "description": "Warren Weaver named organised complexity in “Science and Complexity” (1948), and Jane Jacobs applied it to cities in *The Death and Life of Great American Cities* (1961). Philip Anderson’s “More Is Different” (1972) argued that each level of organisation has its own laws. In 1984 George Cowan, Murray Gell-Mann, David Pines and colleagues from Los Alamos set up the Santa Fe Institute to study such systems across physics, biology and economics. Its early work drew on Stuart Kauffman’s NK landscapes, autocatalytic sets and gene networks, the edge of chaos and Per Bak’s self-organised criticality; Geoffrey West, James Brown and Brian Enquist’s scaling of metabolism (1997) went on to cities. The 2021 Nobel Prize in Physics, half of it to Giorgio Parisi, was given for work on complex physical systems."
  },
  "8": {
    "summary": "Deterministic systems whose sensitivity to initial conditions makes long-range prediction impossible.",
    "description": "Edward Lorenz’s weather model in “Deterministic Nonperiodic Flow” (1963) showed that three simple equations can produce trajectories that never repeat and that diverge from any nearby start. David Ruelle and Floris Takens’s strange attractors (1971) followed, and Tien-Yien Li and James Yorke named the subject in “Period Three Implies Chaos” (1975); Michael Mackey and Leon Glass found it in models of physiological control (1977). Robert May’s review of the logistic map from population ecology, “Simple mathematical models with very complicated dynamics” (1976), Mitchell Feigenbaum’s universal period-doubling constant (1978) and Benoit Mandelbrot’s fractals built the theory, and James Gleick’s *Chaos* (1987) brought it to a general readership. The core results were in by 1990, the last of them chaos control and synchronisation, and the programme then merged into nonlinear dynamics and complexity science."
  },
  "9": {
    "summary": "Systems of many agents that learn and adapt, whose collective behaviour cannot be read off any one agent.",
    "description": "John Holland brought the genetic algorithm and the classifier systems of his Michigan work, evolutionary computation, to the Santa Fe Institute’s 1986 workshop and recast them as a theory of the field’s central object: agents with internal models that aggregate into hierarchies, use tags to interact, and evolve together. Murray Gell-Mann’s schemata, Simon Levin’s work on ecosystems and, later, John Miller and Scott Page’s *Complex Adaptive Systems* (2007) generalised the idea. Agent-based modelling and resilience thinking draw on it. Holland’s last book on the subject was *Signals and Boundaries* (2012)."
  },
  "10": {
    "summary": "The structure of real networks – small worlds, hubs, communities – and how it shapes what spreads on them.",
    "description": "Duncan Watts and Steven Strogatz’s small-world model (1998), named after Stanley Milgram’s experiments in social network analysis, and Albert-László Barabási and Réka Albert’s scale-free networks (1999) showed that social, biological and technological networks share a few structural signatures, and that these can be measured. Mark Newman’s community detection (with Michelle Girvan, 2002) and Alessandro Vespignani’s epidemic models built the toolkit; the statistical physics of percolation and scaling supplied the theory. The programme remains active in higher-order and temporal networks, and feeds complexity economics, epidemiology, the network biology of systems biology and network models of mental disorders and of physiology."
  },
  "11": {
    "summary": "Explaining social patterns by simulating the individuals and local rules that generate them.",
    "description": "Joshua Epstein and Robert Axtell’s Sugarscape (*Growing Artificial Societies*, 1996) turned Thomas Schelling’s checkerboard and John Conway’s Life into a method: specify agents and interactions, run the model, and treat the result as an explanation. Swarm (1996) from Christopher Langton’s group and Uri Wilensky’s NetLogo (1999) made the tools general; Leigh Tesfatsion applied them to economics, Nigel Gilbert to sociology, and Volker Grimm and colleagues brought pattern-oriented modelling from the individual-based models of ecology (2005). Timothy Kohler and George Gumerman’s *Dynamics in Human and Primate Societies* (2000) modelled social and spatial processes with it, a use cultural evolution took up. Epidemic and traffic models keep the method in daily use."
  },
  "12": {
    "summary": "Living systems that persist by minimising variational free energy, a bound on how surprising their sensations are.",
    "description": "Karl Friston proposed in 2005 that perception and learning both minimise a free-energy bound on the surprise of sensory input, a quantity borrowed from the variational methods of Geoffrey Hinton and Peter Dayan. In 2006, with Kilner and Harrison, he added action and named the idea the free-energy principle. “Life as we know it” (2013) extended it to any system with a Markov blanket, from cells to brains, and expected free energy added planning and curiosity. Thomas Parr, Giovanni Pezzulo and Friston’s *Active Inference* (2022) and the papers on Bayesian mechanics set out its current form."
  },
  "13": {
    "summary": "Cybernetics of observing systems, which counts the observer as part of the system being described.",
    "description": "Heinz von Foerster’s Biological Computer Laboratory at Illinois (1958–1976) applied cybernetics to itself, on the grounds that a science of feedback must account for the scientist doing the observing. Margaret Mead’s 1967 keynote to the American Society for Cybernetics, published under von Foerster’s title “Cybernetics of Cybernetics”, named the approach. Gordon Pask’s conversation theory, Ernst von Glasersfeld’s radical constructivism and Humberto Maturana’s biology of cognition developed within it. Von Foerster’s “Cybernetics of Cybernetics” (1979) defined second-order cybernetics as the cybernetics of observing systems, and Niklas Luhmann took the observer into his theory of social systems. From the 1990s the name spread retrospectively, through radical constructivism and the journal *Kybernetes*; after Pask’s death in 1996 and von Foerster’s in 2002 the tradition survives mainly through autopoiesis and enactivism."
  },
  "14": {
    "summary": "Society as systems of communication that reproduce themselves and differentiate by function.",
    "description": "Talcott Parsons’s *The Social System* (1951) made system and function the vocabulary of sociology, and Walter Buckley’s *Sociology and Modern Systems Theory* (1967) recast it with cybernetic feedback. Niklas Luhmann worked in this functionalist line until he took up Humberto Maturana and Francisco Varela’s autopoiesis (“Autopoiesis, Handlung und kommunikative Verständigung”, 1982). *Soziale Systeme* (1984) rebuilt the theory on it, together with Heinz von Foerster’s cybernetics of observing systems, and presents the change as a paradigm shift in systems theory, from open to self-referential systems. In this account social systems consist of communications, not people. They reproduce themselves from their own communications and observe one another, and modern society is differentiated into function systems such as law, economy and science. Maturana rejected the transfer of autopoiesis to communication. *Die Gesellschaft der Gesellschaft* (1997) completed the core theory. His students continue the school, and Elena Esposito took it to fashion, probability and financial futures before carrying its concept of communication into the social science of algorithms (*Artificial Communication*, 2022)."
  },
  "16": {
    "summary": "Perception and action as statistically optimal inference under uncertainty, tested against behaviour.",
    "description": "Helmholtz’s idea of perception as unconscious inference was made quantitative from the mid-1990s, first in the Helmholtz machine (Dayan, Hinton, Neal and Zemel 1995). Experiments (Ernst and Banks 2002; Körding and Wolpert 2004) showed that people weigh sensory cues, and priors against evidence, close to the Bayesian optimum. David Knill and Alexandre Pouget’s “The Bayesian brain” (2004) named the Bayesian coding hypothesis, that the brain represents sensory information as probability distributions, and Pouget and colleagues’ probabilistic population codes proposed how neurons might do so. Pouget and colleagues reviewed the programme in 2013, and it has continued beside predictive processing and active inference, which took up much of it."
  },
  "17": {
    "summary": "Order arising spontaneously in systems held far from equilibrium by a flow of energy.",
    "description": "Ilya Prigogine’s Brussels school showed from 1967 that systems driven far from thermodynamic equilibrium can form dissipative structures – convection cells, chemical clocks – that maintain order by exporting entropy; Prigogine received the 1977 Nobel Prize in Chemistry. Jean-Louis Deneubourg took order through fluctuations to termites’ nest building (1977) and Peter Allen to cities (1979). Hermann Haken’s synergetics (1977) derived the same patterns from order parameters and the slaving principle, and Scott Kelso applied it to coordinated movement. Prigogine and Isabelle Stengers’s *Order out of Chaos* (1984) brought the Brussels ideas, read with Henri Bergson and Alfred North Whitehead, to a general readership. Through Stengers, who turned to the philosophy of science and to Whitehead, the Brussels line also reached the humanities, where Bruno Latour, Manuel DeLanda and complexity sociology draw on it more than on Santa Fe."
  },
  "18": {
    "summary": "The brain as a hierarchy in which each level predicts the one below and passes only prediction errors upward.",
    "description": "In “Predictive coding in the visual cortex” (1999) Rajesh Rao and Dana Ballard explained extra-classical receptive-field effects with a model in which each level predicts the one below and sends only the residual error up. Karl Friston’s work made the hierarchy general, and Andy Clark’s target article “Whatever next?” (2013), which brought the situated and extended mind into it, and Jakob Hohwy’s *The Predictive Mind* (2013) turned it into a philosophy of mind. Anil Seth extended it to interoception and selfhood (2012–2013), and his *Being You* (2021) took it to a general readership. The programme remains active alongside active inference, its formal successor."
  },
  "20": {
    "summary": "The qualitative mathematics of change, studying attractors, stability and bifurcations in phase space.",
    "description": "Henri Poincaré, from his 1881 memoir on curves defined by differential equations to his prize memoir on the three-body problem (1890), replaced solving equations with studying the geometry of all their solutions in phase space, and Aleksandr Lyapunov defined stability in 1892. Mary Cartwright and J. E. Littlewood found chaotic solutions of a forced oscillator in 1945, a result that led through Norman Levinson to Stephen Smale’s horseshoe. George Birkhoff, Aleksandr Andronov and Lev Pontryagin, then Andrey Kolmogorov, Vladimir Arnold and Jürgen Moser (KAM theory) and Smale’s work on structural stability built the modern subject. It is a branch of mathematics; chaos theory, catastrophe theory and the theories of dissipative structures and synergetics take their concepts from it."
  },
  "21": {
    "summary": "Macroscopic laws of matter derived from the statistics of enormous numbers of microscopic parts.",
    "description": "James Clerk Maxwell’s velocity distribution (1859), Ludwig Boltzmann’s entropy formula and H-theorem, and Josiah Willard Gibbs’s ensembles (1902) explained thermodynamics as the statistics of molecules, with temperature, pressure and entropy as properties of large populations of them. Albert Einstein’s Brownian motion (1905) and Lars Onsager’s reciprocal relations (1931) extended it to fluctuations and to systems out of equilibrium. Information theory, phase transitions, dissipative structures and Hopfield networks draw on it, Nicholas Georgescu-Roegen made its entropy law a limit on economic growth (1971), and it is still an active branch of physics."
  },
  "22": {
    "summary": "How matter changes state, and why very different systems behave alike near the critical point.",
    "description": "Ernst Ising’s 1925 model of a magnet, Lev Landau’s theory of order parameters (1937) and Lars Onsager’s exact solution of the two-dimensional Ising model (1944) posed the problem. Leo Kadanoff’s block spins and Kenneth Wilson’s renormalisation group (1971) solved it, showing that near a critical point microscopic details cease to matter and systems fall into universality classes with the same exponents. Giorgio Parisi’s spin-glass theory (1979) extended it to disorder and went on into the statistical physics of optimisation and learning, recognised in Parisi’s share of the 2021 Nobel Prize in Physics. Self-organised criticality, network science, econophysics and complexity science take their ideas of scaling and universality from it, and the study of collective behaviour treats the onset of order in a flock as one of its transitions."
  },
  "24": {
    "summary": "Sudden jumps in behaviour classified as a handful of geometric forms, from folds to cusps.",
    "description": "René Thom’s *Stabilité structurelle et morphogenèse* (1972; English 1975), whose ideas circulated from the mid-1960s, proved that the ways a smoothly controlled system with up to four control factors can jump between states fall into seven elementary catastrophes. Christopher Zeeman applied the cusp widely, from dog aggression to stock markets and prison riots, and the resulting critique (Zahler and Sussmann 1977) discredited the applications. The mathematics survived as singularity and bifurcation theory; the modelling habit passed into chaos theory and ecological regime shifts."
  },
  "26": {
    "summary": "Grids of cells updating by local rules, showing how simple programs produce complex behaviour.",
    "description": "John von Neumann, prompted by Stanislaw Ulam, designed a self-reproducing automaton on a grid in the early 1950s to show that a machine following logical rules can reproduce itself. John Conway’s Game of Life (1970) became a popular pastime, and in *Winning Ways* (1982) Conway, with Berlekamp and Guy, sketched how its gliders could build a universal computer. Stephen Wolfram’s study of the elementary rules (1983), his four classes of behaviour (1984) and *A New Kind of Science* (2002) made cellular automata a research programme, and Matthew Cook’s proof that Rule 110 is universal (presented 1998, published 2004) was its last core result. Artificial life, agent-based modelling and models of urban growth took over its grids and local rules."
  },
  "27": {
    "summary": "Synthesising lifelike behaviour in software and hardware to study life as it could be.",
    "description": "Christopher Langton convened the first artificial life workshop at Los Alamos in 1987 and defined the field as the study of life as it could be, not only as it is. Craig Reynolds’s boids (1987), Thomas Ray’s Tierra (1991), Karl Sims’s virtual creatures evolved by genetic algorithm (1994) and the Avida experiments explored flocking, digital evolution and open-ended novelty, and boids passed into particle swarm optimisation and the study of collective behaviour. Most of the problems in Mark Bedau and colleagues’ “Open Problems in Artificial Life” (2000) are still unsolved, and work on evolved bodies continues in basal cognition and diverse intelligence."
  },
  "28": {
    "summary": "Driven systems that tune themselves to a critical state, where avalanches of every size follow a power law.",
    "description": "Per Bak, Chao Tang and Kurt Wiesenfeld’s 1987 sandpile model showed that a slowly driven system can arrive at criticality on its own, without an external parameter being tuned, and that power-law avalanches and 1/f noise follow. Bak and Kim Sneppen applied it to punctuated evolution. Forest fires, earthquakes and neuronal avalanches (Beggs and Plenz 2003) were proposed as instances. Bak’s *How Nature Works* (1996) claimed more than the evidence supported, and after his death in 2002 the programme merged into the wider study of criticality."
  },
  "29": {
    "summary": "Living systems as networks that produce their own components, and cognition as the sense-making of such a system in its world.",
    "description": "Humberto Maturana and Francisco Varela defined living systems in *De máquinas y seres vivos* (1972) as autopoietic: networks of processes that produce the components that produce the network, closed in organisation while coupled to their surroundings. *The Embodied Mind* (Varela, Thompson and Rosch 1991) extended this into enactivism, which rejects the representational view of cognition held by cognitive science and treats it as embodied action, drawing on phenomenology and Buddhist psychology. The programme also took up Susan Oyama’s developmental systems and Esther Thelen and Linda Smith’s dynamic systems. Hanne De Jaegher and Ezequiel Di Paolo’s participatory sense-making (2007) and Evan Thompson’s *Mind in Life* (2007) developed it, and artificial life and active inference borrowed from it; 4E cognition took it in as its enactive strand. Niklas Luhmann rebuilt the theory of social systems on autopoiesis, a transfer to communication that Maturana rejected."
  },
  "30": {
    "summary": "The mathematics of what rational players do when each one’s outcome depends on the others’ choices.",
    "description": "John von Neumann proved the minimax theorem for two-person zero-sum games in 1928, and with Oskar Morgenstern extended the framework to economics in *Theory of Games and Economic Behavior* (1944). John Nash’s equilibrium (1950) covered non-cooperative games in general. John Harsanyi added incomplete information, and Thomas Schelling focal points and credible commitment. Game theorists have received economics Nobel prizes since 1994, and evolutionary game theory and operations research drew on the field."
  },
  "31": {
    "summary": "Strategies treated as inherited traits, and what evolves when fitness depends on what others in the population do.",
    "description": "John Maynard Smith and George Price’s “The Logic of Animal Conflict” (1973), drawing on W. D. Hamilton’s unbeatable strategy (1967) and Price’s covariance mathematics of selection (1972), replaced rational players with populations of inherited strategies and defined the evolutionarily stable strategy, a Nash equilibrium that selection cannot invade. Peter Taylor and Leo Jonker’s replicator dynamics (1978) described how strategy frequencies change over time, and Josef Hofbauer related them to the Lotka–Volterra equations of population ecology (1981). Robert Axelrod’s computer tournaments (1980) and *The Evolution of Cooperation* (1984) showed how cooperation can evolve among egoists, and Martin Nowak and Robert May’s spatial games (1992) added spatial structure; Robert Boyd and Peter Richerson’s punishment model (1992) carried its stable strategies into cultural evolution. Nowak, Karl Sigmund and colleagues continue the work, mainly on the evolution of cooperation."
  },
  "32": {
    "summary": "Ecosystems and societies as adaptive cycles that can absorb shocks or flip into another regime.",
    "description": "C. S. Holling’s “Resilience and stability of ecological systems” (1973) distinguished resilience, the disturbance a system can absorb without changing state, from engineering stability. He read fishery collapses and spruce budworm outbreaks as shifts between domains of attraction, which later work modelled with catastrophe theory. Lance Gunderson and Holling’s *Panarchy* (2002) added the adaptive cycle and nested scales. Holling, Brian Walker and Carl Folke built the Resilience Alliance (1999), and Folke and Johan Rockström the Stockholm Resilience Centre (2007), around social-ecological systems. Marten Scheffer showed how regime shifts can be anticipated, in lakes and later in mood and migraine. The IPCC now uses its definition, and the planetary boundaries (2009) applied its idea of thresholds to the Earth as a whole."
  },
  "33": {
    "summary": "Economy as an evolving system of interacting agents, out of equilibrium, with increasing returns and lock-in.",
    "description": "W. Brian Arthur’s increasing-returns economics, worked out from 1979 and presented at the Santa Fe Institute’s 1987 economics workshop convened by Kenneth Arrow and Philip Anderson, argued that positive feedback makes outcomes path-dependent and lock-in common. Arthur’s El Farol bar problem (1994), the institute’s artificial stock market (1994), Doyne Farmer’s work on market dynamics, Alan Kirman’s heterogeneous agents and Eric Beinhocker’s synthesis, *The Origin of Wealth* (2006), followed. Econophysics, which physicists built beside it from the mid-1990s, turned the El Farol problem into the minority game; economists of the agent-based school answered with “Worrying trends in econophysics” (2006). After the 2008 crisis, network models of financial contagion and agent-based macroeconomics brought the programme into central-bank research."
  },
  "34": {
    "summary": "Learning as weight adjustment in networks of simple units, from the perceptron to transformers.",
    "description": "Frank Rosenblatt’s perceptron (1958) learned to classify by adjusting connections, building on the McCulloch–Pitts neuron. Marvin Minsky and Seymour Papert’s *Perceptrons* (1969) proved what networks without hidden layers cannot compute, and a long lull followed. John Hopfield’s 1982 network, a spin-glass model, and Geoffrey Hinton and Terry Sejnowski’s Boltzmann machines reconnected the field to statistical mechanics, and David Rumelhart, Hinton and Ronald Williams (1986) made backpropagation the way to train networks with hidden layers. The parallel distributed processing group around Rumelhart and James McClelland made such networks connectionism, a programme within cognitive science that did without explicit rules and symbols. AlexNet (2012) and the transformer (2017) made it the basis of the machine-learning industry, and the 2024 Nobel Prize in Physics to Hopfield and Hinton recognised its roots in physics."
  },
  "37": {
    "summary": "The discipline of modelling and optimising operations and decisions, from wartime radar to linear programming and systems analysis.",
    "description": "Begun at Bawdsey in 1937 as British scientists tuned radar defence, operational research grew under Patrick Blackett into a way of studying operations quantitatively, and Philip Morse’s group (1942) brought it to the US Navy. George Dantzig’s simplex method (1947) gave it linear programming, and RAND’s systems analysis, codified in Charles Hitch and Roland McKean’s *The Economics of Defense in the Nuclear Age* (1960), extended it to strategy and federal budgeting. Its critics came from inside it. C. West Churchman and Russell Ackoff, authors of an early textbook (1957), turned to systems thinking, and Ackoff’s “The Future of Operational Research Is Past” (1979) declared its paradigm exhausted, while Jay Forrester built system dynamics against the management science of his day. Its American societies (1952, 1953) merged as INFORMS in 1995."
  },
  "38": {
    "summary": "Ecosystems as energy circuits, with trophic flows measured, diagrammed and simulated for the whole system.",
    "description": "Eugene Odum’s *Fundamentals of Ecology* (1953) put energy flow at the centre of ecology, and his brother Howard T. Odum’s “Trophic structure and productivity of Silver Springs, Florida” (1957) produced the first full energy budget of an ecosystem. The International Biological Programme (1964–1974) funded ecosystem-scale modelling, and Bernard Patten’s four-volume *Systems Analysis and Simulation in Ecology* (1971–1976) made simulation standard. Howard Odum’s energy systems language, set out by 1971 in *Environment, Power and Society*, and his emergy accounting of the 1990s were the programme’s last major contributions. Resilience thinking took over its view of the ecosystem as a whole, and Robert Costanza, Howard Odum’s doctoral student, carried its accounting of energy and value into ecological economics (1989)."
  },
  "39": {
    "summary": "Cognition and agency as properties of cells and tissues, with bioelectric signals steering the body’s form.",
    "description": "Michael Levin’s Tufts group and the basal-cognition community argue that problem-solving is not confined to brains. In their account cells and tissues navigate anatomical and physiological spaces, and bioelectric patterns in tissues store a memory of the target form that growth and regeneration work towards. Founding statements appeared in 2015 (Pezzulo and Levin; Pamela Lyon’s “The cognitive cell”; Friston, Levin, Sengupta and Pezzulo), and Xenobots (2020, with Josh Bongard) supplied an engineered proof of concept. The programme is young and contested, and anthrobots (2023) and wide press coverage have made it known well beyond biology."
  },
  "40": {
    "summary": "Organisms as communities, from the cell as merged bacteria to the body as a host that develops with its microbes.",
    "description": "Lynn Margulis argued in 1967 that mitochondria and chloroplasts descend from free-living bacteria taken in by other cells. Konstantin Mereschkowski and Boris Kozo-Polyansky had proposed as much in Russia decades earlier. Margulis saw Khakhina’s *Concepts of Symbiogenesis* (1992) and Kozo-Polyansky’s *Symbiogenesis* (2010) into English, while Mereschkowski’s papers reached English in translation (Martin and Kowallik 1999). Ribosomal RNA sequences confirmed her account from 1975, and sequence phylogenies (Schwartz and Dayhoff 1978) added to the evidence. From 2007 the claim widened to holobionts, hosts such as corals, squid and mammals that develop with their microbes, a term Margulis coined in 1990–1991 independently of Adolf Meyer-Abich (1943). Margaret McFall-Ngai and colleagues’ “Animals in a bacterial world” (2013) set out the programme; Nancy Moran and others have criticised the hologenome concept."
  },
  "41": {
    "summary": "Life and its planet as one self-regulating system.",
    "description": "James Lovelock came to Gaia through the search for life on Mars. With Dian Hitchcock, in “Life detection by atmospheric analysis” (1967), he argued that a living planet shows itself in an atmosphere far from chemical equilibrium. He named the hypothesis in 1972 and, with Lynn Margulis, who supplied the microbial mechanisms, framed it in 1974 as homeostasis of the atmosphere by the biosphere. Lovelock read Gaia through cybernetics, Margulis increasingly through autopoiesis. Darwinian critics (Doolittle 1981; Dawkins 1982) asked how natural selection could produce regulation at the scale of a planet, and Andrew Watson and Lovelock’s Daisyworld model (1983) was the first answer. Timothy Lenton, Doolittle himself and Bruno Latour have since returned to the question."
  },
  "42": {
    "summary": "The Earth studied as one coupled system of atmosphere, oceans, ice, rock and life.",
    "description": "NASA’s Earth System Sciences Committee under Francis Bretherton drew its diagram of the coupled Earth in 1986, and the International Geosphere-Biosphere Programme (1987–2015) built an international field around it. Its physical core is climate modelling, from Syukuro Manabe’s general circulation models to Klaus Hasselmann’s stochastic climate models, which built on Edward Lorenz; Manabe and Hasselmann shared the 2021 Nobel Prize in Physics with Giorgio Parisi. The Amsterdam Declaration of 2001 described the Earth as a single self-regulating system. Whether the field descends from Gaia is disputed. Leading Earth system scientists name Gaia as one inspiration (Steffen and colleagues 2020), while an archival study (Barton 2023) finds no trace of it in NASA’s committee papers."
  },
  "43": {
    "summary": "Thresholds at which the Earth system can tip, and the safe operating space for human activity inside them.",
    "description": "Paul Crutzen and Eugene Stoermer proposed in 2000 that humanity had entered the Anthropocene. Timothy Lenton’s team named the tipping elements of the climate system in 2008, and in 2009 Johan Rockström, Will Steffen and colleagues set out nine planetary boundaries, building on ecological economics’ question of the economy’s scale, Earth system science, C. S. Holling’s resilience and the limits to growth. Many tipping elements are modelled as bifurcations, and critical slowing down gives early warning of them. Updates led by Steffen (2015) and Katherine Richardson (2023) found more boundaries crossed, six of nine by 2023, and the 2025 check found seven. Work on positive tipping points towards sustainability draws on transitions research (Lenton and colleagues, 2022)."
  },
  "44": {
    "summary": "Human groups as parts of ecosystems, with ritual as a regulator.",
    "description": "Clifford Geertz’s *Agricultural Involution* (1963) compared Indonesian farming systems as ecosystems. Roy Rappaport’s *Pigs for the Ancestors* (1968), drawing on Odum’s ecology, read the ritual cycle of the Maring of New Guinea as a homeostat that kept pigs, people and gardens in balance, and his essay “Ritual, sanctity, and cybernetics” (1971) made the model explicit. Andrew Vayda treated human populations as one ecological population among others. In “New directions in ecology and ecological anthropology” (1975) Vayda and Bonnie McCay criticised the approach’s assumption of equilibrium, and symbolic, historical and political ecologies replaced it in the 1980s. Tim Ingold’s relational anthropology grew partly out of that critique."
  },
  "45": {
    "summary": "Society traced as networks of human and non-human actors, without an overarching system.",
    "description": "Michel Callon, Bruno Latour and Madeleine Akrich built actor-network theory at the Centre de Sociologie de l’Innovation of the Paris École des Mines in the 1980s, with John Law in Britain, first to explain how scientific facts and technologies are made. Scallops, microbes and instruments count as actors alongside people, and a society is held together by networks of translation, which Latour held to be more supple than a system. In 2012 Latour and colleagues turned the approach against agent-based models, arguing that there is more complexity in the elements than in the aggregates. Latour took up Alfred North Whitehead’s critique of the bifurcation of nature (2004) and carried the approach into the Anthropocene, with Isabelle Stengers’s cosmopolitics and his Gaia work with Timothy Lenton, until his death in 2022. Annemarie Mol’s studies of medicine continue it."
  },
  "46": {
    "summary": "Ethnography of how humans, fungi, forests and microbes make worlds together.",
    "description": "Tim Ingold’s *The Perception of the Environment* (2000) joined Gregory Bateson’s ecology of mind, Gibson’s ecological psychology and Susan Oyama’s developmental systems into an anthropology of organisms in their environments. Multispecies ethnography followed with Eduardo Kohn’s *How Forests Think* (2013), built on the semiotics of Peirce and of the biosemiotician Terrence Deacon, Anna Tsing’s *The Mushroom at the End of the World* (2015) and Marisol de la Cadena’s *Earth Beings* (2015). Donna Haraway’s *Staying with the Trouble* (2016) set sympoiesis, making-with, against the self-making of autopoiesis and joined it to Lynn Margulis’s symbiogenesis. She took the term from Beth Dempster, who had coined it within systems theory in 1998. Tsing’s *Feral Atlas* (2020) maps the patchy Anthropocene."
  },
  "47": {
    "summary": "Matter, societies and bodies as assemblages whose parts keep capacities of their own.",
    "description": "Manuel DeLanda’s *A Thousand Years of Nonlinear History* (1997) read cities, economies and languages as dissipative structures, a materialist history in the line of Gilles Deleuze and Félix Guattari. *Intensive Science and Virtual Philosophy* (2002) rebuilt Deleuze’s process ontology – the virtual, intensity, multiplicity – in the analytic terms of state spaces, attractors and bifurcations. *A New Philosophy of Society* (2006) built on it a theory of Deleuze and Guattari’s assemblage (*agencement*), in which wholes emerge from parts that remain detachable. Karen Barad’s agential realism (*Meeting the Universe Halfway*, 2007) and Jane Bennett’s *Vibrant Matter* (2010) widened it into the new materialisms, a name DeLanda and Rosi Braidotti, a Deleuzian too, each coined independently in the late 1990s. Dave Snowden draws on DeLanda for Cynefin."
  },
  "48": {
    "summary": "Complexity as a way of thinking across disciplines, set against its reduction to models.",
    "description": "Edgar Morin, who died in May 2026, came to cybernetics in 1968, to Gregory Bateson and general systems theory at the Salk Institute (1969–1970) and, back in France, through Henri Atlan to John von Neumann’s automata and Heinz von Foerster’s order from noise. From them he built *La Méthode* (1977–2004) and the complex thought of *Introduction à la pensée complexe* (1990). In 2005 he called the Santa Fe programme restricted complexity, still inside the epistemology of classical science, and set general complexity against it. Paul Cilliers’s *Complexity and Postmodernism* (1998) read complex systems through connectionism and Derrida, and his Stellenbosch students Rika Preiser and Minka Woermann joined his critical complexity to Morin’s. Alicia Juarrero’s *Dynamics in Action* (1999) grounded intentional action in dissipative structures and context-sensitive constraints."
  },
  "49": {
    "summary": "Societies as open, dissipative systems, studied case by case more than by simulation.",
    "description": "Michael Reed and David Harvey’s “The new science and the old” (1992) and their dissipative social systems (1994) joined complexity to Bhaskar’s critical realism, and David Byrne carried this complex realism into case-based social science. John Urry’s *Global Complexity* (2003) and “The complexity turn” (2005) brought complexity into sociology and cultural theory, and Sylvia Walby used it to rethink how systems of inequality intersect (2007), against Niklas Luhmann’s closed systems. Byrne and Gill Callaghan’s *Complexity Theory and the Social Sciences: The State of the Art* (2014) set this European line against Santa Fe’s micro-emergence by simulation. Brian Castellani’s map of the complexity sciences and the CECAN evaluation centre (from 2016) continue it."
  },
  "50": {
    "summary": "Organisations, health care and policy understood as complex adaptive systems.",
    "description": "Ralph Stacey’s *The Chaos Frontier* (1991) and “The science of complexity” (1995) brought chaos, self-organisation and complex adaptive systems into strategy. At Hertfordshire he, Patricia Shaw and Douglas Griffin then moved to complex responsive processes of relating, and in *Complexity and Management* (2000) asked whether complexity was a fad or a radical challenge to systems thinking. Brenda Zimmerman’s *Edgeware* (1998, with Curt Lindberg and Paul Plsek) and her simple, complicated and complex problems (2002, with Sholom Glouberman) took complexity into health care, as did Plsek and Trish Greenhalgh’s *BMJ* series, opened by “The challenge of complexity in health care” (2001). Mary Uhl-Bien’s complexity leadership theory (2007) and the Overseas Development Institute’s *Exploring the Science of Complexity* (2008) carried it into leadership and aid."
  },
  "51": {
    "summary": "A sense-making framework that tells ordered, complex and chaotic situations apart.",
    "description": "Dave Snowden began Cynefin at IBM in 1999, and Cynthia Kurtz co-created its 2003 form (Kurtz and Snowden 2003), with the domains known, knowable, complex and chaotic. In the complex domain one probes first, with parallel safe-to-fail experiments, then senses and responds. Its account of constraints comes from Alicia Juarrero, and its view of complexity draws on Paul Cilliers and Manuel DeLanda. Snowden set it against systems thinking, which he placed in the knowable domain, and against agent-based simulation of people, who carry identity and intent; the name anthro-complexity comes from this. The Harvard Business Review article with Mary Boone, “A leader’s framework for decision making” (2007), spread it, and the EU’s field guide *Managing complexity (and chaos) in times of crisis* (2021) applied it."
  },
  "52": {
    "summary": "How communities govern shared resources without a state or a market, at many scales at once.",
    "description": "Vincent Ostrom, Charles Tiebout and Robert Warren introduced polycentricity in “The Organization of Government in Metropolitan Areas: A Theoretical Inquiry” (1961). Elinor Ostrom’s *Governing the Commons* (1990) showed with fisheries, forests and irrigation systems that users often manage common-pool resources better than the tragedy of the commons predicts, and distilled design principles for institutions that last. With Vincent Ostrom at their Bloomington Workshop she built the Institutional Analysis and Development framework, tested it with game-theoretic experiments, and in 2009 published a framework for social-ecological systems in *Science*. Her Nobel lecture that year was titled “Beyond Markets and States: Polycentric Governance of Complex Economic Systems”. Marco Janssen’s agent-based models and the resilience community carry the work on."
  },
  "53": {
    "summary": "Development as the self-organisation of body, brain and world over nested timescales.",
    "description": "In “Self-organizing systems and infant motor development” (1987) Esther Thelen, Scott Kelso and Alan Fogel treated infant kicking and stepping as patterns that self-organise from body, task and environment, not as motor programmes unfolding in the brain. Thelen and Linda Smith’s *A Dynamic Systems Approach to the Development of Cognition and Action* (1994) made the case for all of development, and Gregor Schöner’s dynamic field theory gave it models, such as that of the A-not-B error (2001). Tim van Gelder and Randall Beer argued in the 1990s that cognition itself is dynamical, not the computation over symbols that cognitive science took it to be. After Thelen’s death in 2004 the approach passed into enactivism, where Evan Thompson built on it."
  },
  "54": {
    "summary": "The mathematics of how populations grow, compete, prey on one another and coexist in communities.",
    "description": "Alfred Lotka’s *Elements of Physical Biology* (1925) and Vito Volterra (1926) wrote predator and prey as coupled equations whose numbers cycle, and in the 1930s Georgy Gause showed in the laboratory that two competing species cannot share one niche for long. G. Evelyn Hutchinson defined the niche as a hypervolume of conditions (1957), and Robert MacArthur and E. O. Wilson’s *The Theory of Island Biogeography* (1967) made an island’s species a balance of immigration and extinction. Robert May found that random communities lose stability past a threshold of size, connectance and interaction strength (1972), and chaos in the simplest population model (1974). C. S. Holling defined resilience on its predator–prey and outbreak dynamics (1973), and Peter Turchin carried its population dynamics into the rise and fall of states (2003). Chaos theory and evolutionary game theory took dynamics from the field, and agent-based modelling its individual-based models."
  },
  "55": {
    "summary": "The mathematical theory of evolution as changing gene frequencies under selection, drift, mutation and migration.",
    "description": "Ronald Fisher’s paper of 1918 on the correlation between relatives reconciled Mendel’s genes with the continuous variation the biometricians measured. Fisher’s *The Genetical Theory of Natural Selection* (1930), Sewall Wright’s “Evolution in Mendelian populations” (1931) and J. B. S. Haldane’s *The Causes of Evolution* (1932) made selection, drift, mutation and migration a mathematics of gene frequencies. It became the core of the modern synthesis, which Theodosius Dobzhansky, Ernst Mayr and Julian Huxley, who named it (1942), carried to species. W. D. Hamilton’s inclusive fitness (1964), Motoo Kimura’s neutral theory (1968) and George Price’s covariance equation (1970) extended it. Evolutionary game theory, the genetic algorithm and the models of cultural evolution were built on it, and the extended evolutionary synthesis defines itself against its gene-centred framework."
  },
  "56": {
    "summary": "How changes in embryonic development make evolutionary change, and why distant animals build their bodies with the same genes.",
    "description": "Stephen Jay Gould’s *Ontogeny and Phylogeny* (1977) revived the study of changes in the timing of development, which the modern synthesis had left out of evolutionary theory, and a Dahlem workshop in Berlin in 1981 set the agenda of a new field. The homeobox, found in 1984 in the fruit fly’s homeotic genes by Walter Gehring’s group in Basel, showed that distant animals lay out their bodies with one family of Hox genes. Brian Hall’s *Evolutionary Developmental Biology* (1992) gave the field a textbook under its name, and Neil Shubin, Cliff Tabin and Sean Carroll’s deep homology (1997) traced new organs to an ancient genetic toolkit. Gerd Müller and others carried its questions of developmental bias, modularity and evolvability into the extended evolutionary synthesis."
  },
  "57": {
    "summary": "Cells and organisms as networks of interacting molecules, measured at scale and modelled as dynamical systems.",
    "description": "Mihajlo Mesarović’s symposium *Systems Theory and Biology* (1968) and Stuart Kauffman’s random genetic nets (1969) treated the cell as a system decades before the data existed. Genome sequencing supplied them: in 2000 Leroy Hood and colleagues founded the Institute for Systems Biology in Seattle and Hiroaki Kitano convened the first International Conference on Systems Biology in Tokyo. Kitano’s overview in *Science* (2002), whose first reference is Norbert Wiener’s *Cybernetics* and which cites John Tyson’s bifurcation analyses of the cell cycle, put robustness at the centre, and Uri Alon’s network motifs (2002) came from network science. Maureen O’Malley and John Dupré distinguished (2005) a pragmatic, data-driven stream from a systems-theoretic one, which Denis Noble carried into the debate on evolution; Michael Levin’s group found kinds of memory in its gene-regulatory network models (2021), a strand of basal cognition. Much of the field is omics and parameter fitting rather than complexity research."
  },
  "58": {
    "summary": "Social structure studied as patterns of ties between people and groups, with its own measures of position and connection.",
    "description": "Jacob Moreno’s sociometry (*Who Shall Survive?*, 1934) drew the attractions and rejections within a group as sociograms. Stanley Milgram’s small-world experiments (1967) traced chains of acquaintance across the United States, and Mark Granovetter’s “The strength of weak ties” (1973) argued that acquaintances carry news that close friends do not. Harrison White’s group at Harvard made networks a structural sociology of roles and positions (1976), and Linton Freeman clarified the measures of centrality (1978) and founded the journal *Social Networks*. Stanley Wasserman and Katherine Faust’s *Social Network Analysis* (1994) became the standard text. Both founding papers of network science cite this literature, and Freeman pointed out (2008) that the centrality measures the physicists used had come from it."
  },
  "59": {
    "summary": "The mind as an information-processing system that computes over symbols, studied by psychology, linguistics, philosophy and artificial intelligence.",
    "description": "The summer research project at Dartmouth that John McCarthy, Marvin Minsky, Nathaniel Rochester and Claude Shannon proposed in 1955 named artificial intelligence, and in 1956 Allen Newell and Herbert Simon’s Logic Theory Machine proved theorems by manipulating symbols while George Miller measured the limits of short-term memory in bits. The field took cognition to be computation over representations. Jerry Fodor’s *The Language of Thought* (1975), Newell and Simon’s physical symbol system hypothesis (1976) and David Marr’s levels of analysis (*Vision*, 1982) set out this view, and the journal *Cognitive Science* (1977) and its society (1979) gave it institutions. Minsky and Seymour Papert’s *Perceptrons* (1969) turned symbolic AI against neural networks. Connectionism, enactivism, the dynamical approach and embodied and extended cognition defined themselves against its cognitivism."
  },
  "60": {
    "summary": "Optimisation, design and learning by simulated evolution, and by the collective rules of insect colonies and flocks.",
    "description": "Three schools began in the 1960s: Lawrence Fogel’s evolutionary programming, Ingo Rechenberg and Hans-Paul Schwefel’s evolution strategies in Berlin, and John Holland’s genetic algorithm at Michigan, whose theory of adaptive systems drew on Ronald Fisher’s population genetics from 1962 and which *Adaptation in Natural and Artificial Systems* (1975) set out. David Goldberg’s textbook (1989) and John Koza’s *Genetic Programming* (1992) spread the methods, and journals of the 1990s joined the schools under one name. Swarm intelligence came from insect colonies and flocks: Marco Dorigo’s ant system (1991–1996) from the Brussels models of trail-laying ants, and James Kennedy and Russell Eberhart’s particle swarm optimisation (1995) from simulated birds. The field is judged on benchmarks; Holland carried its mechanisms into complex adaptive systems."
  },
  "61": {
    "summary": "Evolution in which development, plasticity, inheritance beyond genes and niche construction are causes of selection, not only its products.",
    "description": "Massimo Pigliucci asked in 2007 whether evolutionary theory needed an extended synthesis; a workshop he and Gerd Müller held in Altenberg in 2008 led to *Evolution – the Extended Synthesis* (2010). Its themes come from evo-devo and ecology: developmental bias, plasticity that leads while genes follow, the inheritance of epigenetic states (Eva Jablonka and Marion Lamb), and niche construction (John Odling-Smee, Kevin Laland and Marcus Feldman, 2003), whose authors came to it from models of cultural evolution. Laland and colleagues argued the case in *Nature* (2014) and set out its structure in 2015, in which organisms shape the selection that shapes them. Denis Noble’s biological relativity (2012), in which no level of a living system has privileged causal power, is its radical wing. Critics such as Douglas Futuyma answer that the standard theory already accounts for them."
  },
  "62": {
    "summary": "Life as a web of sign relations between organisms and their worlds, from the genetic code to animal communication.",
    "description": "Jakob von Uexküll’s Umwelt (1909), the world an animal’s senses and actions make, and Thomas Sebeok’s zoosemiotics of the 1960s were its precursors. Sebeok and Jean Umiker-Sebeok’s *Biosemiotics* (1992) gathered the field, and in Copenhagen and Tartu Jesper Hoffmeyer, Claus Emmeche and Kalevi Kull built it on Peirce’s signs, which are relations, and read life as a web of them, from the code duality of a genome and the body that reads it to an animal in its Umwelt. “Theses on biosemiotics” (2009), by Kull, Terrence Deacon and others, set out its programme. Hoffmeyer claimed Gregory Bateson as an ancestor (2008), Denis Noble’s critique of the modern synthesis appeared in its journal *Biosemiotics* (2021), and Eduardo Kohn’s *How Forests Think* (2013) builds on Deacon."
  },
  "63": {
    "summary": "The economy as a part of the biosphere, bounded by thermodynamics and by what ecosystems can supply and absorb.",
    "description": "Kenneth Boulding’s spaceship Earth (1966), Nicholas Georgescu-Roegen’s *The Entropy Law and the Economic Process* (1971) and Herman Daly’s *Steady-State Economics* (1977) argued that the economy runs on low-entropy matter and energy from a finite biosphere and cannot grow without limit. In 1989 Robert Costanza, a doctoral student of Howard T. Odum, opened the journal *Ecological Economics*, beside a new international society. Its questions are the scale of the economy against the biosphere’s capacity, a fair distribution and the value of natural capital; Costanza and colleagues’ estimate of the value of the world’s ecosystem services (1997) made the last an instrument of policy. The degrowth debate carries it on, and the planetary boundaries (2009) took its question of scale to the Earth as a whole."
  },
  "64": {
    "summary": "Cities as self-organising systems whose form is fractal and whose wealth, innovation and infrastructure scale with their size.",
    "description": "Alan Wilson’s entropy-maximising models of flows in cities (1970) and Peter Allen’s self-organising central places (1979) were its precursors. Michael Batty and Paul Longley’s *Fractal Cities* (1994) read urban form as growth from the bottom up, and Batty joined cellular automata and agent-based models into simulations of cities, while Juval Portugali built on Hermann Haken’s synergetics and Denise Pumain’s Paris school modelled systems of cities. At the Santa Fe Institute Luís Bettencourt, Geoffrey West and colleagues found (2007) power laws by which wealth and patents grow faster than population with city size, and infrastructure slower. Elsa Arcaute, Batty and colleagues found (2015) that the laws depend on where a city’s boundary is drawn; the two schools debate it in one literature."
  },
  "65": {
    "summary": "How flocks, schools and swarms move as one body, ordered by local rules among neighbours.",
    "description": "Tamás Vicsek and colleagues (1995) let each of many self-driven particles turn towards the average heading of its neighbours and found that, below a critical noise, a disordered crowd begins to move together; John Toner and Yuhai Tu showed the same year why such a flock can hold long-range order in two dimensions. Biologists brought the models to animals: Camazine, Deneubourg and colleagues’ *Self-Organization in Biological Systems* (2001), Iain Couzin and colleagues’ models of animal groups (2002) and David Sumpter’s principles of collective animal behaviour (2006). Andrea Cavagna, Irene Giardina, Giorgio Parisi and colleagues found that each starling in a flock attends to six or seven neighbours whatever their distance (2008). Active matter, the physics of self-propelled units, grew out of the same work."
  },
  "66": {
    "summary": "The statistical physics of markets and societies, from scaling in prices, correlations and wealth to models of opinion and consensus.",
    "description": "Rosario Mantegna and H. Eugene Stanley found in 1995 that the fluctuations of a stock index scale like a physical system near a critical point; the field was named econophysics at the second Statphys-Kolkata conference that year, and Stanley and colleagues put the name in print in 1996. Jean-Philippe Bouchaud, Marc Potters and colleagues read the correlations between stocks through random-matrix theory (1999), Damien Challet and Yi-Cheng Zhang turned W. Brian Arthur’s El Farol problem into the minority game (1997), and Adrian Drăgulescu and Victor Yakovenko modelled money as energy in a gas of exchanges (2000). Sociophysics, which Serge Galam began with a mean-field model of a strike (1982), is its social branch: voter, Sznajd and bounded-confidence models of opinion, reviewed by Claudio Castellano, Santo Fortunato and Vittorio Loreto (2009)."
  },
  "67": {
    "summary": "Cognition as spread across brain, body, tools and other people, rather than computed inside the head.",
    "description": "Rodney Brooks’s robots, which acted without central representations (“Intelligence without representation”, 1991), Edwin Hutchins’s account of ship navigation as cognition distributed across a crew and its instruments (*Cognition in the Wild*, 1995) and Andy Clark and David Chalmers’s extended mind (1998), in which a notebook can hold part of a memory, set three camps against the cognitivism of cognitive science. Lawrence Barsalou’s perceptual symbols (1999) and Margaret Wilson’s six views of embodied cognition (2002) carried the programme into psychology, where most of its literature lies. Meetings in 2006 and 2007 brought the embodied, embedded, extended and enactive strands under one name, 4E cognition (Richard Menary’s special issue, 2010; *The Oxford Handbook of 4E Cognition*, 2018), and Clark went on to predictive processing."
  },
  "68": {
    "summary": "Culture as a second system of inheritance, explained by the summed effects of individuals learning from one another, with the models of population genetics and evolutionary games.",
    "description": "Luigi Luca Cavalli-Sforza and Marcus Feldman’s *Cultural Transmission and Evolution* (1981) and Robert Boyd and Peter Richerson’s *Culture and the Evolutionary Process* (1985) brought the population thinking of genetics to culture: individuals learn from parents, teachers and peers under biases such as conformity, and the models sum their learning into the change of a population. Boyd and Richerson’s punishment model (1992) made evolutionary game theory an account of cooperation in large groups, Joseph Henrich tied the loss of skills in Tasmania to the number of people learning from one another (2004), and Peter Turchin’s cliodynamics (*Historical Dynamics*, 2003) took population dynamics to the rise and fall of states. Alex Mesoudi, Andrew Whiten and Kevin Laland set out a unified science of cultural evolution (2006). Laland, John Odling-Smee and Feldman joined gene–culture models to niche construction (2000), which the extended evolutionary synthesis took up. Critics such as Tim Ingold answer that culture is not a population of traits but grows in people’s relations with one another and with their surroundings."
  },
  "69": {
    "summary": "Reality as made of processes and events rather than of enduring substances.",
    "description": "Henri Bergson’s *Creative Evolution* (1907) set duration and creative becoming against the timeless world of mechanics, and Alfred North Whitehead’s *Process and Reality* (1929) built a “philosophy of organism” of actual occasions that come to be by taking up, or prehending, those before them. Charles Hartshorne carried it into theology and Nicholas Rescher into analytic philosophy (*Process Metaphysics*, 1996). Gilles Deleuze built a process ontology of difference and becoming on Bergson (*Le Bergsonisme*, 1966; *Différence et répétition*, 1968) and Whitehead’s event (*Le Pli*, 1988); Manuel DeLanda’s reconstruction of it grounds assemblage theory. Ilya Prigogine and Isabelle Stengers read irreversibility through Whitehead (*Order out of Chaos*, 1984); Stengers and Bruno Latour carried him into science studies, Donna Haraway into multispecies anthropology, and Daniel Nicholson and John Dupré’s *Everything Flows* (2018) took process into biology."
  },
  "70": {
    "summary": "Mental disorders as networks of symptoms that cause one another and can tip into states that sustain themselves.",
    "description": "Denny Borsboom proposed in 2008 that a mental disorder may be a causal network of symptoms rather than a hidden condition that produces them, and Angélique Cramer, Lourens Waldorp, Han van der Maas and Borsboom set out the network perspective in “Comorbidity: A network perspective” (2010): disorders occur together through the symptoms they share. The Amsterdam group found the small-world structure of network science among the symptoms of DSM-IV (2011) and estimates symptom networks from data with the Ising model of physics. With Marten Scheffer, Ingrid van de Leemput and Marieke Wichers found critical slowing down before shifts into and out of depression (2014). Borsboom’s “A network theory of mental disorders” (2017) treats disorders as alternative stable states of strongly connected networks, held in place by hysteresis. Richard McNally carried the approach to post-traumatic stress; the programme’s own reviews note that networks estimated from cross-sectional data do not show which way the causes run."
  },
  "71": {
    "summary": "Disease as a change in the dynamics of physiological control, and health as a complex, fractal variability that ageing and illness erode.",
    "description": "Michael Mackey and Leon Glass showed in 1977 that delay equations for breathing and blood-cell production can oscillate or behave chaotically, and read respiratory and blood disorders as dynamical diseases, illnesses marked by striking changes in the dynamics of a bodily function. Glass, Michael Guevara and Alvin Shrier found period-doubling bifurcations in stimulated heart cells (1981), and Glass and Mackey’s *From Clocks to Chaos* (1988) surveyed the rhythms of life. At Harvard Medical School, Ary Goldberger’s group turned the question round: a healthy heartbeat fluctuates in a complex, fractal way, contrary to the classical idea of homeostasis, and loses that complexity with age and disease (Lipsitz and Goldberger 1992). With H. Eugene Stanley’s physicists they measured it with scaling methods from statistical physics, such as detrended fluctuation analysis (1995), and PhysioNet (2000) made physiological recordings freely available. Plamen Ivanov’s network physiology (2012) maps how organ systems interact, and critical slowing down has been proposed as a warning of attacks in chronic disease (2016)."
  },
  "72": {
    "summary": "How energy, mobility and food systems shift to sustainable configurations, through niches, regimes and landscape, and how such transitions can be governed.",
    "description": "Frank Geels’s multi-level perspective (2002) explains a transition, such as the shift from sailing ships to steamships, as innovations growing in protected niches until pressure from the wider landscape opens the dominant socio-technical regime; it draws on evolutionary economics and on science and technology studies, Bruno Latour’s and Michel Callon’s among them. René Kemp, Johan Schot and Remco Hoogma had proposed strategic niche management (1998), and Jan Rotmans, Kemp and Marjolein van Asselt transition management (2001), which Derk Loorbach set out as a “complexity-based governance framework” (2010), drawing on the theory of complex adaptive systems and on Holling’s panarchy. With technological innovation systems these are the field’s founding frameworks (Markard, Raven and Truffer 2012). Its research network was inaugurated in 2009 and its journal, *Environmental Innovation and Societal Transitions*, first appeared in 2011; it also informs the study of positive tipping points. Elizabeth Shove and Gordon Walker proposed replacing the multi-level perspective with social practice theory (2010), one of the criticisms Geels answered in 2011."
  }
}