Societies come together slowly, but can fall apart quickly, say researchers who applied the tools of evolutionary biologists to an anthropological debate.

Using archaeological records and linguistic analyses rather than fossils and genes, they created an evolutionary tree of political forms once found in Pacific islands.

The study, published October 13 in Nature, was intended to illuminate an issue of contention among archaeologists, anthropologists and historians: whether societies become more complex in incremental steps or sudden bursts, and whether they dissolve in similar fashion.

"The evolution of complex societies since the end of the last ice age has long been a major topic of investigation and debate," wrote researchers led by anthropologists Thomas Currie and Ruth Mace of University College, London. "These debates have continued largely in the absence of rigorous, quantitative tests."

According to the classic academic narrative of political evolution, post-ice age complexity – defined as increasing levels of social hierarchy – evolved slowly but surely, with mechanical predictability. First came egalitarian bands of closely-related people; then came larger but still-egalitarian tribes, with only informal leadership; these clustered into chiefdoms, with hereditary leaders; chiefdoms united into states, with bureaucracies and administrative offices.

To some scholars, however, this narrative is deterministic. They say that political evolution doesn't proceed neatly from lower to higher complexity, but proceeds in bursts. To them, tribes, chiefdoms and states all represent distinct evolutionary trajectories rather than stages of a single progression. The critics also say that the tendency of societies to move from higher to lower complexity has been underestimated.

Making it all the more difficult to settle the debate is its basis in an incomplete archaeological record. But "just as evolutionary biologists use phylogenetic trees constructed using genetic data to test evolutionary hypotheses, anthropologists have recently begun to use cultural phylogenetics to test hypotheses about human social and cultural evolution," wrote Currie and Mace.

The researchers focused their attention on Austronesia, a general name for Pacific islands inhabited by the descendants of people who left Taiwan 5,200 years ago and eventually settled much of southeast Asia and Oceania, from Madagascar in the west to Easter Island in the east.

As Austronesian settlers moved from island to island, their language bifurcated again and again, taking unique local forms that in many cases persist to this day. By comparing the languages, other researchers had been able to reconstruct a chronological narrative of the islands' settlement.

Over 84 societies in this tree, Currie and Mace overlaid what's known from archaeological records of their social structure, which underwent "spectacular political differentiation to give rise to examples of the entire range of political organization," wrote Collapse author Jared Diamond in an accompanying commentary.

When they compared the resulting tree to trees generated by computational models of different anthropological narratives – linear and stepwise, varied and lurching – the researchers found a close match to the linear. Political complexity indeed grew slowly, bit by bit, with no sudden jumps from bands to chiefdoms or tribes to states.

"Political evolution, like biological evolution, tends to proceed through small steps rather than through major jumps in ‘design space,'" wrote Mace and Currie.

However, purely forward-marching models didn't fit the data. There was evidence of societies marching backwards as well, and this didn't follow the same step-by-step path. Societies could collapse.

The study will undoubtedly be criticized, especially for its rough categorization of subtle political differences into four hierarchical categories, wrote Diamond. But what's most important is that the techniques of evolutionary biologists can be applied to anthropology.

Most anthropologists interpret the past "by narrative accounts of individual cases, less often by narrative comparisons of selected cases, and infrequently by comprehensive narrative surveys," Diamond wrote. "My first reaction to Currie and colleagues' paper was one of surprise: why hadn't we used their method before, because it is so obviously superior?"

According to Diamond, cultural phylogenies might be devised for societies in southern and central Africa, which have highly diverse languages and rich political histories.

Analyzing political evolution in Europe and central Asia, where most languages have gone extinct and cultures have long intermingled, is "the grand challenge," he said.

Image: 1) Easter Island moai, 13th-16th century./Flickr, Robert Nyman. 2) Gateway to the royal compound of the 11th Paramount Chief of Tonga, circa 13th century./Thomas Currie.

See Also:

Citations: "Rise and fall of political complexity in island South-East Asia and the Pacific." By Thomas E. Currie,, Simon J. Greenhill, Russell D. Gray, Toshikazu Hasegawa & Ruth Mace. Nature, Nature, Vol. 467 No. 7317, September 9, 2010.

"Political evolution." By Jared Diamond. Nature, Nature, Vol. 467 No. 7318, September 9, 2010.

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