A sorghum field, with houses and hills behind, in Mandara Mountains, Cameroon

In the eighteenth century, the British New World colony of South Carolina prospered from the raising and exporting of rice. What does this have to do with linguistics, agriculture and development in the modern day? The answer is a salutary warning against unexamined assumptions: African agricultural technology created the prosperity of colonial Carolina.

Many centuries before, peoples of the Guinea Coast of Africa evolved a sophisticated and highly efficient technology for growing abundant crops of African rice, Oryza glaberima. Taking advantage of the tidal estuaries of rivers flowing into the Atlantic, they built levees and channels to redirect the ebb and flow of the tides onto their fields. Before the planting season, African farmers channeled to their fields salty seawater flowing into the estuaries at high tide. Some days or weeks later, they let fresh water flow onto the plots: the salty water had killed the weeds and seeds, and then the fresh water washed away the salty water and leached the salt from the soil. At the same time, it deposited a fresh layer of silt, enriching the soil for the rice crop to be planted.

Carolina planters gained access to this technology in the eighteenth century by importing experts from the Guinea Coast. But unlike modern-day expatriate advisers, these experts crossed the Atlantic not as a privileged group but as slaves, and so their seminal role in colonial Carolina agriculture long remained unnoticed. Only in the past twenty years, through the work of scholars, such as Professor Judith Carney and Dr. Edda Fields, has their contribution finally begun to gain the recognition it has long deserved.

The story of the Guinea Coast rice farmers is simply one example of the immense diversity of African agricultural inventiveness over the long course of history-and a relatively late example at that. We now know that the history of cultivation and livestock-raising in Africa extends almost 11,000 years ago. By 8500 BCE, at about the same time as peoples in the Middle East began for the first time to cultivate wheat and barley, African communities living more than 1,000 kilometres to the south separately and independently became the earliest known raisers of cattle in the world. By around 7000-6000 BCE, the descendants of these first cattle keepers started also to cultivate crops. The early staple of their "Sudanic" agriculture was sorghum, now a crop of almost worldwide importance (see photos, courtesy of the author).

Still another independent invention of agriculture took place in West Africa among early inhabitants speaking languages of the Niger-Congo family. The West African cultivation ideas are also very old, possibly dating as long ago as 9000-7000 BCE. The early staple of this agriculture was probably the Guinea yam, but West African farmers also domesticated a number of other crops, now well known outside Africa, including okra and black-eyed peas (cow-peas). Over the past 4,000 years in the more western parts of West Africa, another crop, African rice, replaced yams in importance.

Archaeology provides part of our knowledge of this history, but a great many areas of Africa remain still poorly known to archaeologists. So, in African historical studies, scholars have turned increasingly to linguistic reconstruction of the past.

How does language evidence reveal history? Every language, by its very nature, is a historical archive. The documents in this archive are the words that make up the vocabulary of the language and each word has a history of its own. A particular word may have been in use through many ancestral stages in the language's history, or it may have come into use only at some intermediate stage. In that case, it might derive from an existing older word in the language: for example, in English, "worker" was coined by adding a suffix to the much older verb, "work". Alternatively, a word might first have come into use as a word borrowed (adopted) from another language.

Every language has a huge vocabulary capable of expressing the full range of the knowledge and culture of its speakers. If, for example, we can show that a word meaning "cow" goes far back in a language's history, we then know that the people have known about cows for all that time. Conversely, when a word is borrowed from one language to another, the reason may be that the item named by the word is also new. For instance, the English term banana was borrowed from Portuguese, which in turned came from one of several African languages of the Guinea Coast that have this word. The history of the word banana reveals the route of the spread of the fruit: from West Africa via the Portuguese to the English and other Europeans. The job of the linguistically-trained historian is to uncover large numbers of such individual word histories and then meld their testimony into a coherent story about the past.

Let us turn back to African rice. Botanists tell us that the cultivated kinds of Oryza glaberima originated in the regions of the Inland Delta of the Niger River, in modern-day Mali. On the linguistic side, the oldest root words for rice cultivation in West Africa go back to the proto-Mande language. "Proto-Mande" is our name for the common ancestor language of the widespread Mande branch of the Niger-Congo family. Modern-day Mande languages include Kpelle in Liberia, Mende in Sierra Leone, and Bamana, Malinke and Soninke in Mali. Scholars believe that the proto-Mande language was spoken by a society that lived somewhere in or close to the Inland Delta, just where rice cultivation originated.

Sorghum is a major African contribution to world agriculture.

The overall history of rice in West Africa went something like this. In around the third millennium BCE, the proto-Mande people greatly enhanced their agricultural productivity by domesticating African rice, indigenous to the wetland environments of the Inland Delta. With this economic advantage, the proto-Mande society grew in numbers and territory. Gradually, after 2000 BCE, the society broke apart into a number of daughter societies, as the descendants of the proto-Mande spread wider and wider southward, bringing rice cultivation into new areas. In the hinterland of the Guinea Coast, local peoples who were not of the Mande group adopted rice growing from their Mande neighbours. But because they lived in a much different kind of wetland environment along the estuaries, they set about inventing a new technology to make cultivation possible. Much later, in the seventeenth and eighteenth centuries, their de-scendants took that technology with them to North America.

African agricultural history offers salutary insights to those interested in agricultural development in any part of the world, not just in Africa. It reminds us that people everywhere possess thousands of years of accumulated expertise on domestic animals, crops, soils and climate, and on appropriate technologies. Expanding the productivity of agriculture will work best if the full body of local knowledge informs the application of outside expertise. The most successful projects are likely to be those that begin with a component that elicits local bodies of knowledge. For Africa, the growing literature on agricultural history written by linguistic-historical scholars provides a valuable deep-time perspective. Equally important, learning from local people is likely to better engage those people themselves in the project and enlist their interest in its solutions.