Now, a provocative new study suggests the fates of societies hinged on a subtler problem with these plants. And if it’s right, it could dramatically complicate the popular theory of the agriculture-driven dawn of civilization that has appeared in textbooks for generations.
The study, published last year by economists at the United Kingdom and Israel doing novel work on archaeological and anthropological evidence, attempts to explain a strange pattern in agricultural practices. The most advanced civilizations all tended to cultivate grain crops, like wheat and barley and corn. Less advanced societies tended to rely on root crops like potatoes, taro and manioc.
It’s not that grains crops were much easier to grow than tubers, or that they provided more food, the economists say. Instead, the economists believe that grains crops transformed the politics of the societies that grew them, while tubers held them back.
“Since the grain has to be harvested within a short period and then stored for use until the next harvest, a visiting tax collector could readily confiscate part of the stored produce,” the authors write. In ancient China, for instance, the famously bureaucratic government depended on a seasonal tax on grain harvests.
Using an anthropological database, the economists gathered information about the political sophistication of societies before the 1500s. They knew whether regions were organized by tribes, by chiefdoms, or by large, elaborate states. They also knew what the major crop in each society was.
In ancient Africa, Asia and Europe, for instance, societies had access to a large catalog of different grains, including barley, sorghum, wheat and rice. They also had access to one root crop, the yam. And in the ancient Americas, societies had access to one kind of grain, corn and three different kinds of root crops — white potatoes, sweet potatoes and cassava.
These maps show a clear correlation between crop choice and political complexity. Societies that grew grain tended to have more hierarchical political systems — empires, even — like the rice- and wheat-cultivating kingdoms of ancient India. Tuber crops were associated with smaller, more local political units.