What’s the magic ingredient to make your civilization grow? If you thought agriculture, good guess but wrong. Same with religion, trade, or a big population. No, the really necessary item to turn large groups of individuals into a culture just may be ... war. Preferably intense warfare, with cavalry.
That’s sort of the Twitter version of a new paper that uses evolutionary biology to predict where complex societies will arise and then compares its results to where they did. Lead author Peter Turchin of the University of Connecticut-Storrs and three co-authors experimented with a computer model trying to explain quantitatively how “human societies evolve from small groups, integrated by face-to-face cooperation, to huge anonymous societies of today.” As they explain in the Proceedings of the National Academies of Science, the variable in their simulation that best explained what made people band together and create the relatively costly impedimenta of empire was warfare.
Backward testing their model on the Europe-Asia-Africa landmass between 1500 B.C.E. and 1500 C.E., the spread of big societies was accurately predicted 65 percent of the time, while a model that omitted the diffusion of military technology was accurate only 16 percent of the time. Of course, identifying what leads to the rise (and fall) of civilizations has been an academic parlor game for centuries (and a computer game for decades). It’s even a public fascination—witness bestselling authors ranging from Gibbon to Diamond—while a look at any library’s history shelves will suggests that military exploits have an outsize fascination for those playing along. What makes this latest effort at explanation somewhat unique is that it’s based on math:
Social scientists have proposed a number of theories to explain the emergence of large-scale societies, emphasizing such factors as population growth, warfare, information management, economic specialization, and long-distance trade. However, because existing theories are usually formulated as verbal models, the causal mechanisms underlying these theories are not always made explicit.
Their “conceptual core” relied on the following domino effect: the spread of military technology leads to more intense warfare, which spawns “ultrasocial” traits to evolve, which is the precursor to large-scale societies. Another key variable was geography, in particular broad plains that allow big armies range to run and, perhaps more importantly, to control subjugated areas. Mountainous areas are too easy to defend.
By running the numbers looking specifically at warfare, the team has been able to tease out just how important at least that theoretical agent is. Like many military simulation games, the researchers broke the known world into 100 x 100 kilometer squares, and coded those squares for the existence of agriculture, its elevation, and what sort of land cover it had. They then “seeded” military technology in promising looking cells—i.e. those along the steppes (which, vitally, also had horses ready to be weaponized). And voilà:
As in the real data, the ﬁrst imperiogenesis hotspots appear in Mesopotamia, Egypt, and North China because these areas are situated near the steppe frontier, and that is where [military technology] diffuse ﬁrst, tipping the selection in favor of ultrasocial traits.
The later rise of empires that aren’t mainly upon the plain arises, they theorize, from that diffusion of war-making know-how. I'm sure the ancient Egyptians were in a tizzy over the "chariot gap" in their days.
If this seems a little too pat, know that the authors tend to agree with you. Their primary goal was to show how a data-driven approach can join with the precepts of evolutionary biology to answer, or at least narrow, big historical questions.
While that approach—Turchin has dubbed it “clioldynamics”—may seem fairly uncontroversial, it’s often not a welcome weapon in the modern historian’s arsenal, as this fine piece from Nature demonstrates: “Most think that phenomena such as political instability should be understood by constructing detailed narratives of what actually happened — always looking for patterns and regularities, but never forgetting that each outbreak emerged from a particular time and place.”
In this latest paper, Turchin doesn’t deny the power of the unique, but neither is he seduced by it:
Undoubtedly, the rise and fall of individual states and empires will be complex, involving idiosyncratic and contingent events. Our analyses, however, also provide support for the idea that the story of the past is not just a case of “one damned thing after another,” but that there are general mechanisms at play in shaping the broad patterns of history.