In his 1997 bestseller “Guns, Germs and Steel,” historian Jared Diamond argued that the availability of nutritious and easily domesticated plants and animals gave some societies a head start. In the Middle East there was barley and wheat; in Asia there was millet and rice. “People around the world who had access to the most productive crops became the most productive farmers,” Diamond later said on his PBS show. And more productivity led to more advanced civilizations.
Going against the generally accepted theory are those societies that depended on tubers (such as potato, tapioca and sweet potato) as their main cultivated food source. These societies had an abundance of food, tubers are generally more productive and nutritious than grains, but never developed the technical and political complexity of societies that depended on grains.
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.So grains can easily be stolen or taxed. There for they more easily support an infrastructure to defend them, on built on the gains from taxing them.
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.
How crops changed the world
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.