Shea trees - which produce nuts used to make the prime soap, moisturizer and lotion ingredient shea butter - were harvested by humans in West Africa more than 1,000 years earlier than previously thought, says a new study.
The wild trees were used as early as A.D. 100, found the researchers in the course of excavating an archaeological site at Kirikongo, which is in western Burkina Faso. In Africa, there is only a narrow belt of well-drained savannah in which shea trees grow, from West Africa to East Africa.
The trees, Vitellaria paradoxa, also have termite-resistant wood that is used in construction and to make implements.
In the study, University of Oregon archaeologists looked at carbonized nutshell fragments - thousands of them - that were located in layers that signified households built atop one another for about 1,600 years.
"Our findings demonstrate the antiquity of the use of this particular resource," noted Daphne E. Gallagher in the UO Department of Anthropology. "It demonstrates the importance of wild foods in early agricultural diets, and that its importance has continued through time."
The trees were nurtured for potential harvest even during climate-change periods, Gallagher said. Other now-common crops, like millet and sorghum, were managed around the wild shea trees.
"In the layers, we've found exterior shells that have been knocked off the nuts," Gallagher said. "When a household first starts using shea, nutshells are all over the place. Some are thick. Some are thin. There is a huge range of variability. As households become established, the shells become more consistent and thinner. This is reflecting that trees are being brought into these cultivation systems."
Processing these nuts to produce oil is a lot of work, said Gallagher. "The nuts on trees in Burkina Faso produce a Crisco-like fat," she said. "Those in eastern Africa have a different chemical composition that produces more of a liquid that has to be stored in something like a milk jug. It's not as widely used."
Previous reports had pointed to shea tree use as early as A.D. 1100. Pushing back the time period of this practice shows how little is yet known about Western Africa, Gallagher said.
The findings were published in the Journal of Ethnobiography.
Follow Catherine Arnold on Twitter at @TreesWhales.
