The best revolutions end in topplings—of statues, regimes, and Weinsteins. Others prove to be more smoke than flame. While heady days of Occupy Wall Street are long over, the national conversation they ignited about economic inequality still smolders. Since protesters decamped from Zuccotti Park, Thomas Piketty has become a household name, a populist has claimed the presidency, and universal basic income has gone from fantastical subreddit to serious policy proposal.
Among developed countries, the United States has the most dramatic—which is to say, the worst—income inequality of any democracy in the world. Today, the top 1 percent of American earners take home 24 percent of the income. The nation's wealth gap is even more startling, with One Percenters controlling more wealth than the bottom 90 percent.
But just how deep do the roots of inequality go? Is economic disparity of a hallmark of modernity—or a persistent feature of human civilization? A recent study, led by Washington State University archaeologist Timothy Kohler and published in Nature, offers some new insights on inequality across human history, in both the New and Old Worlds.
Inequality is typically measured using a Gini coefficient—named for Italian statistician Corrado Gini, who introduced the metric in 1912—and ranges from zero to one. (A society where everyone earns the same income has a Gini coefficient of zero, while a society where one person earns every dollar and everyone else takes home nothing has a coefficient of one.) But indicators are only as good as the numbers behind them. Clean economic data is notoriously hard to come by, even in the year 2017, and Hellenistic societies weren't as diligent of record keepers as, say, the United States Census Bureau.
Kohler's team needed a universal proxy for wealth. Burial sites were problematic (maybe only rich people were buried), as were abandoned artifacts (anyone fleeing a settlement probably took their most valuable possessions). Instead, the researchers hit on the idea of house size. In antiquity, as today, homes were an indicator both of status and income.
By measuring the difference in house sizes at various archaeological sites, Kohler and his colleagues were able to calculate Gini coefficients for those societies. Settlements where every domicile had nearly the same footprint had Gini indexes closer to zero, or less economic disparity. Sites with marked differences between the largest homes and the smallest had higher Gini coefficients, or more disparity.
In the end, Kohler's team looked at 63 different settlements, spanning four continents and 11,000 years, from hunter-gatherer societies to ancient cities.
"One of the things it showed, which was no surprise, was that even small-scale societies had some degree of inequality," he says. Hunter-gatherer societies revealed the least disparity, while agricultural sites showed the most. "As people become more reliant on agriculture, they begin to settle down. As they settle down, they transmit resources from one generation to the next." Soon, wealth accrues to particular families and lineages.
But Kohler and colleagues also discovered an unexpected trend in the data. At sites in both the Americas and Eurasia, the disparity of wealth grew in parallel fashion for the first 2,500 years after the advent of agriculture in the area. "But then, in the New World, the increase in wealth differences flattened out, whereas it kept increasing in the Old World."
The researchers hypothesize that the menagerie of large, domesticable animals available in Europe—but not in the Americas—was responsible for the societies' divergent trajectories. Europe had cattle, pigs, horses, sheep, and goats. The Americas had llamas and, well, dogs. An early European with a team of oxen could easily "extensify"—that is, expand geographically—the amount of land he was cultivating, Kohler explained, whereas pre-Columbian tribes had to till every inch of soil by hand, often with digging sticks. Plow animals weren't just sources of milk, meat, and manure—they were force multipliers.
Agricultural extensification in Europe "probably did a couple things simultaneously," Kohler says. "First, it raised the amount of surplus in a society. Imagine everyone is a subsistence farmer, just scraping by. You can't have much in the way of wealth difference. You need a surplus that can be seized or redistributed by the elites. Second, not all households could afford a team of oxen. You had to be relatively well off, and then you could rent your animals out to those that didn't have them."
As oxen-owning European landowners increased their holdings, they slowly squeezed out their livestock-less neighbors. "By medieval times, a class of landless peasants develops in the Old World," Kohler says. "Agricultural extensification increased wealth disparities at both ends: the rich got richer and the poor got poorer."
As compelling as the question of where economic inequality comes from is the question of where it leads.
"Understanding inequality is a difficult business," Kohler says. "In many ways, [inequality] can represent a creative, entrepreneurial society. On the other hand, Joseph Stiglitz and others have written about the ills of inequality. In the U.S., social mobility has decreased quite a bit since the 1950s, probably related to wealth inequality." The essential paradox of disparity is that it's an indicator both of economic strength and of social fragility.
"Well functioning societies tend to increase their wealth disparities over time," Kohler says. "What's disturbing is that it's not easy to see how a country like the United States backs off levels of high inequality without a major cataclysm."