NEWS IN FOCUS CYCLES OF VIOLENCE The motivating issues vary, but episodes of violent political upheaval in the United States are surprisingly regular. NUMBER OF 80 VIOLENT EVENTS ~920 PER 5 YEARS Racial tensions, unrest among workers and anticommunist feeling surged in the aftermath ~870 of the First World War. 60 Racial, class and political tensions peaked during and after the Civil War. ~970 40 The civil-rights movement, social change and opposition to the Vietnam War marked the tumultuous 1960s. 20 POLITICAL LABOUR OR ECONOMIC RACIALLY MOTIVATED 0 VIGILANTE 780 800 820 840 860 880 900 920 940 960 980 2000 HISTORY AS SCIENCE Advocates of ‘cliodynamics’ say that they can use scientific methods to illuminate the past. But historians are not so sure. BY LAURA SPINNEY trends and outbursts of violence in the United States, and has come to the conclusion that ometimes, history really does seem to a new wave of internal strife is already on its 1 repeat itself. After the US Civil War, for way . The peak should occur in about 2020, 1 SOURCE: REF. example, a wave of urban violence fuelled he says, and will probably be at least as high as Sby ethnic and class resentment swept across the one in around 1970. “I hope it won’t be as the country, peaking in about 1870. Internal bad as 1870,” he adds. strife spiked again in around 1920, when race Turchin’s approach — which he calls clio­ riots, workers’ strikes and a surge of anti- dynamics after Clio, the ancient Greek muse of Communist feeling led many people to think history — is part of a groundswell of efforts to that revolution was imminent. And in around apply scientific methods to history by identify- 1970, unrest crested once more, with violent stu- ing and modelling the broad social forces that dent demonstrations, political assassinations, Turchin and his colleagues say shape all human riots and terrorism (see ‘Cycles of violence’). societies. It is an attempt to show that “history To Peter Turchin, who studies population is not ‘just one damn thing after another’”, says dynamics at the University of Connecticut in Turchin, paraphrasing a saying often attributed Storrs, the appearance of three peaks of politi- to the late British historian Arnold Toynbee. cal instability at roughly 50-year intervals is not Cliodynamics is viewed with deep scepti- a coincidence. For the past 15 years, Turchin cism by most academic historians, who tend has been taking the mathematical techniques to see history as a complex stew of chance, that once allowed him to track predator–prey individual foibles and one-of-a-kind situa- cycles in forest ecosystems, and applying them tions that no broad-brush ‘science of history’ to human history. He has analysed historical will ever capture. “After a century of grand records on economic activity, demographic theory, from Marxism and social Darwinism to 24 | NATURE | VOL 488 | 2 AUGUST 2012 | CORRECTED 8 AUGUST 2012 © 2012 Macmillan Publishers Limited. All rights reserved FEATURE NEWS structuralism and postmodernism, Periods of rioting and upheaval most historians have abandoned have recurred roughly every 50 the belief in general laws,” said Rob- years in US history. ert Darnton, a cultural historian at BETTMANN/CORBIS Harvard University in Cambridge, expectancies — and wealth ine- Massachusetts, in a column written quality, measured by the ratio of in 1999. the largest fortune to the median Most think that phenomena wage. Choosing appropriate prox- such as political instability should 1871 ies can be a challenge, because rel- be understood by constructing evant data are often hard to find. detailed narratives of what actu- No proxy is perfect, the researchers ally happened — always looking concede. But they try to minimize for patterns and regularities, but the problem by choosing at least never forgetting that each out- two proxies for each variable. break emerged from a particular Then, drawing on all the sources time and place. “We’re doing what they can find — historical data- can be done, as opposed to aspiring bases, newspaper archives, ethno- after what can’t,” says Daniel Szechi, graphic studies — Turchin and his who studies early-modern history colleagues plot these proxies over at the University of Manchester, time and look for trends, hop- UK. “We’re just too ignorant” to ing to identify historical patterns identify meaningful cycles, he adds. and markers of future events. For But Turchin and his allies con- example, it seems that indicators TOPICAL PRESS AGENCY/GETTY PRESS TOPICAL tend that the time is ripe to revisit of corruption increase and politi- general laws, thanks to tools such 1926 cal cooperation unravels when a as nonlinear mathematics, simu- period of instability or violence lations that can model the inter­ is imminent. Such analysis also actions of thousands or millions of allows the researchers to track the individuals at once, and informat- order in which the changes occur, ics technologies for gathering and so that they can tease out useful analysing huge databases of his- correlations that might lead to torical information. And for some cause–effect explanations. academics, at least, cliodynamics can’t come a moment too soon. ENDLESS CYCLES “Historians need to abandon the When Turchin refined the con- habit of thinking that it’s enough cept of cliodynamics with two col- to informally point to a sample of leagues — Sergey Nefedov of the cases and to claim that observations Institute of History and Archaeol- generalize,” says Joseph Bulbulia, ogy in Yekaterinburg, Russia, and who studies the evolution of reli- 1967 Andrey Korotayev of the Russian N. BOENZI/NEW YORK TIMES CO./GETTY TIMES N. BOENZI/NEW YORK gion at Victoria University of Wel- State University for the Humani- lington in New Zealand. ties in Moscow — the researchers found that two trends dominate FROM ECOLOGY TO HISTORY the data on political instability. Turchin conceived cliodynamics The first, which they call the secu- during what he jokingly calls a lar cycle, extends over two to three midlife crisis: it was 1997, he was centuries. It starts with a relatively 40 years old, and he had come to egalitarian society, in which supply feel that all the major ecological questions about population dynamics and demand for labour roughly balance out. In time, the population had been answered. History seemed to be the next frontier — perhaps grows, labour supply outstrips demand, elites form and the living stand- because his father, the Russian computer scientist Valentin Turchin, had ards of the poorest fall. At a certain point, the society becomes top-heavy also wondered about the existence of general laws governing societies. with elites, who start fighting for power. Political instability ensues and (The elder Turchin’s dissident writings about the origins of totalitarian- leads to collapse, and the cycle begins again. ism were among the reasons that the Soviet Union exiled him in 1977, Superimposed on that secular trend, the researchers observe a shorter after which he moved his family to the United States.) cycle that spans 50 years — roughly two generations. Turchin calls this What is new about cliodynamics isn’t the search for patterns, Turchin the fathers-and-sons cycle: the father responds violently to a perceived explains. Historians have done valuable work correlating phenomena social injustice; the son lives with the miserable legacy of the resulting such as political instability with political, economic and demographic conflict and abstains; the third generation begins again. Turchin likens variables. What is different is the scale — Turchin and his colleagues this cycle to a forest fire that ignites and burns out, until a sufficient are systematically collecting historical data that span centuries or even amount of underbrush accumulates and the cycle recommences. millennia — and the mathematical analysis of how the variables interact. These two interacting cycles, he says, fit patterns of instability across In their analysis of long-term social trends, advocates of cliodynam- Europe and Asia from the fifth century bc onwards. Together, they ics focus on four main variables: population numbers, social structure, describe the bumpy transition of the Roman Republic to the Roman state strength and political instability. Each variable is measured in sev- Empire in the first century bc. He sees the same patterns in ancient eral ways. Social structure, for example, relies on factors such as health Egypt, China and Russia, and says that they explain the timing of last inequality — measured using proxies including quantitative data on life year’s Egyptian uprising, which took the regime of then-president 2 AUGUST 2012 | VOL 488 | NATURE | 25 © 2012 Macmillan Publishers Limited. All rights reserved NEWS FEATURE Hosni Mubarak by surprise. At the time, the Egyptian economy was scepticism among historians in general. The essential weakness of any growing and poverty levels were among the lowest in the developing attempt to make predictions based on trends, says Szechi, is the appall- world, so the regime could reasonably have expected stability. In the ing patchiness of historical information. Records can be preserved or decade leading up to the revolution, however, the country saw a quadru- destroyed by chance: in 1922, for example, fighting in the Four Courts pling of graduates with no prospects — a marker of elite overproduction area of Dublin during the Irish Civil War led to a fire that destroyed the and hence, Turchin argues, trouble. country’s entire medieval archive. More generally, says Szechi, knowl- Turchin has also applied this approach to other historical puzzles, edge tends to pool around narrow subject areas. “We can tell you in great such as how religions grow. Several models have been proposed. One is detail what the grain prices were in a few towns in southern England that they grow in a linear fashion as nonbelievers spontaneously ‘see the in the Middle Ages,” he says.