How did complex human society develop? It's a question that will be familiar to players of the computer game Civilisation – in which lowly tribes can become mighty empires. Now, a simulation similar to the game is shedding some light. It models 3000 years of human history, the first to do so on such a scale.
In order for small, roving bands of nomadic humans to evolve into the organised societies we see today, social behaviours, such as trust between ethnic groups, and social institutions such a government, a justice system, formal education and a unifying religion, needed to develop.
But how did they arise? To find out if warfare played a role, Peter Turchin of the University of Connecticut and his colleagues built a civilisation simulator to predict where and when complex societies arose.
Like Civilisation, the model breaks the world into squares – or in this case, the Eurasian continent – and characterises them according to the type of land present, how mountainous it was, and if it was farmed. Every farmed square was inhabited by an independent group of humans, which could either be organised or not. Military technologies were seeded in squares close to the Eurasian steppe – where horses were first harnessed by humans – and gradually diffused outwards as the simulation ran.
The researchers ran the model between the years 1500 BC, when organised groups were few and far between, and AD 1500. When compared with historical records, it predicted where and when large empires would form and persist with 65 per cent accuracy. When they removed the influence of military technologies from the picture, this fell to 16 per cent.
Removing the effects of elevation from the model only reduced the accuracy to 48 per cent, suggesting that warfare played a more important role than geography in determining which groups stabilised into societies. Turchin says warfare exerted a selection pressure on early groups of people, forcing them to work together to form a society – or be wiped from the map.
That's because, although many measures were of little benefit to the individual – paying taxes, for example – they helped forge more coordinated, and therefore stronger societies that were able to outcompete less organised groups.
While the idea that warfare drives social evolution isn't new, Turchin is the first to test it. William Thompson, a political scientist who researches conflict and international relations at Indiana University in Bloomington, says Turchin's model offers insights into the dynamics of societal change. "There has been very little of this model testing done over long time periods. Instead, we argue back and forth over what was influential without any hope of resolving the debates."
"If we can figure out what influences what over the long term, we can do a better job of modelling processes that are ongoing," says Thompson.
Turchin is now planning to model the rise of complex societies in the Americas, as well as extending his model of Eurasian history beyond AD 1500.
However, running a similar model for the modern world will be much more complicated, says Dirk Helbing of the Swiss Federal Institute of Technology in Zurich, who is working on such a model. This is because war and violent conquest are no longer the primary ways in which social institutions and culture spread. Mass media, migration and globalisation would all have to be taken into account, he says.
Journal reference: PNAS, doi.org/nxj
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