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.
The argument depends on the differences between how grains and tubers are grown. Crops like wheat are harvested once or twice a year, yielding piles of small, dry grains. These can be stored for long periods of time and are easily transported — or stolen.
Root crops, on the other hand, don’t store well at all. They’re heavy, full of water, and rot quickly once taken out of the ground. Yuca, for instance, grows year-round and in ancient times, people only dug it up right before it was eaten. This provided some protection against theft in ancient times. It’s hard for bandits to make off with your harvest when most of it is in the ground, instead of stockpiled in a granary somewhere. More fertile regions did not necessarily yield more complex societies.
But the fact that grains posed a security risk may have been a blessing in disguise. The economists believe that societies cultivating crops like wheat and barley may have experienced extra pressure to protect their harvests, galvanizing the creation of warrior classes and the development of complex hierarchies and taxation schemes.
“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.
Societies that grew grain tended to have more hierarchical political systems — empires, even.
Low productivity leads to low agricultural surpluses leads to less complex societies.
The Incas developed a way of freeze-drying potatoes by leaving them out at high elevations. This technology allowed them to treat potatoes like a grain: non-perishable, transportable and taxable.
Increasingly, anthropologists say that the key to understanding the rise of civilization is to study political and religious institutions. Many now believe that societies took up farming not out of necessity but for cultural reasons — to please a king or to satisfy their religion.