Tracking the Lost Crops of the Ancient World
More than 10,000 varieties of plant foods have bolstered the diets of modern humans at various times and places. During the last 10 millennia, 16 types of grasses, comprising more than 40 species, have been used in various locales around the globe, says Xinyi Liu, an assistant professor of archaeology. But today’s food web, in calorific terms, is dominated by just three grasses: wheat, rice, and maize. Why did we lose the broad-spectrum food strategy that sustained the ancient world?
Why some crops became globally important in the last 400 years, while others were ‘lost’ in our modern food-webs, remains a bit of a mystery, says Liu, but “changes in ecological, culinary, and cultural importance all played roles.”
Elucidating such shifts – how humans caused some crops to spread across or disappear from various regions – is one focus of Liu’s Laboratory for the Analysis of Early Food-Webs. Recently, Liu and his colleagues have been increasingly drawn to the ‘missing’ half of the ancient cereals, particularly around 30 taxa originating from several continents and collectively known as millets. These include the Chinese millets, Indian millets, and African millets, which share some common features, such as a short growing season, modest water requirements, and C4 photosynthesis. In a project funded by the International Center for Advanced Renewable Energy and Sustainability (I-CARES) at Washington University, Liu and his team apply archaeology, stable isotope analysis, paleoethnobotany, and archaeogenetics to explore the ancient world with C4 photosynthesis.
Our modern food webs were shaped by two episodes of ‘food globalization’ in the past, Liu explains. One was over the oceans, and the other was over the lands. Over the last 400 years, in the context of ‘Columbian Exchange,’ plants and animals originating from the Americas were brought to Eurasia, and Eurasian foods and diseases expanded to the New World. Earlier still, between c. 7,000 and 4,000 years ago, the Eurasian landmass underwent a tremendous exchange of cereal crops. For example, wheat and barley from southwest Asia expanded to East Asia, and Chinese millets also spread to Europe in those millennia. Liu’s research has focused on the timing, pathways and driving forces of those exchanges.
Liu has partnered on this project with Fiona Marshall, who directs archaeological fieldwork in East Africa. Researchers in both groups will work together to explore dietary history by looking into archaeological bones and the stable isotopic signatures on those bones. The ultimate question is the roots of African millet consumption.
Rachel Reid, a postdoctoral researcher from Liu’s group, is currently studying millet specimens housed at the University of Illinois to gather carbon and nitrogen isotopic baselines. These millet landraces were collected from Africa by legendary American botanist Jack Harlan in the 1960s. Such data will help the researchers piece together when and how these cereal crops contributed to Eastern African diet and cuisine.
Liu’s research in other areas of the world has shed light on the patterns, pathways, and driving forces behind cereal crop movements. Evidence of millet consumption in the northern Tibetan Plateau and Kazakhstan, for example, shows swaps between the two locales. Evidence from Kazakhstan shows that people first ate founder crops such as wheat and barley before switching to millets around 4,000 years ago. On the Tibetan Plateau, in western China, the pattern is reversed: data indicate that humans first relied on millets before incorporating wheat and barley roughly four millennia ago.
Although researchers debate what drives swaps such as these, Liu says that a region’s culinary system likely becomes fixed first, then cultures choose to domesticate crops that fit their palates.
Although globalization and capitalism have tended to blur early ecological, culinary, and cultural signatures, some ancient preferences are still in place today, Liu notes. Eastern cultures have long relied on grains that can be boiled and steamed, and thus sticky starches tend to dominate their cuisines. European cultures had an early preference for grains that could be ground and used in baking, so flour has long played an important role in that continent’s cuisine.