Researchers at Washington State University and 13 other institutions have found that the arc of prehistory bends towards economic inequality.

In the largest study of its kind, the researchers saw disparities in wealth mount with the rise of agriculture, specifically the domestication of plants and large animals, and increased social organization.

Their findings, published last month in the journal Nature, have profound implications for contemporary society, as inequality repeatedly leads to social disruption, even collapse, said Tim Kohler, lead author and WSU Regents professor of archaeology and evolutionary anthropology at WSU. The United States, he noted, currently has one of the highest levels of inequality in the history of the world.

“Inequality has a lot of subtle and potentially pernicious effects on societies,” Kohler said.

The study gathered data from 63 archaeological sites or groups of sites. Comparing house sizes within each site, researchers assigned Gini coefficients, common measures of inequality developed more than a century ago by the Italian statistician and sociologist Corrado Gini. In theory, a country with complete wealth equality would have a Gini coefficient of 0, while a country with all the wealth concentrated in one household would get a 1.

The researchers found that hunter-gatherer societies typically had low wealth disparities, with a median Gini of .17. Their mobility would make it hard to accumulate wealth, let alone pass it on to subsequent generations. Horticulturalists — small-scale, low-intensity farmers — had a median Gini of .27. Larger scale agricultural societies had a media Gini of .35.

To the researchers’ surprise, inequality kept rising in the Old World, while it hit a plateau in the New World, said Kohler. The researchers attribute this to the ability of Old World societies “to literally harness big domesticated mammals like cattle and eventually horses and water buffalo,” Kohler said.

Draft animals, which were not available in the New World, let richer farmers till more land and expand into new areas. This increased their wealth while ultimately creating a class of landless peasants.

“These processes increased inequality by operating on both ends of the wealth distribution, increasing the holdings of the rich while decreasing the holdings of the poor,” the researchers write.

The Old World also saw the arrival of bronze metallurgy and a mounted warrior elite that increased Ginis through large houses and territorial conquests. [Continue reading…]