A new study published on July 10 in the Proceedings of the Royal Society B by archaeologists from Washington University in St. Louis, the University of Pittsburgh, and their colleagues presents the most extensive archaeobotanical record from interior east Africa.
Previously, scientists struggled to gather ancient plant remains from east Africa, leaving gaps in understanding where and how early plant farming began in Kenya, Tanzania, and Uganda.
"There are many narratives about how agriculture began in east Africa, but there's not a lot of direct evidence of the plants themselves," explained Natalie Mueller, an assistant professor of archaeology at Washington University in St. Louis and co-first author of the study. The research took place at the Kakapel Rockshelter in the Lake Victoria region of Kenya.
"We found a huge assemblage of plants, including a lot of crop remains," Mueller said. "The past shows a rich history of diverse and flexible farming systems in the region, in opposition to modern stereotypes about Africa."
The research indicates a pattern of gradual introduction of various crops from different parts of Africa.
Notably, cowpea remnants found at Kakapel Rockshelter, directly dated to 2,300 years ago, represent the earliest documented arrival of a domesticated crop in eastern Africa. Cowpea, believed to have originated in west Africa, likely arrived in the Lake Victoria basin with Bantu-speaking peoples migrating from central Africa, the study authors noted.
"Our findings at Kakapel reveal the earliest evidence of domesticated crops in east Africa, reflecting the dynamic interactions between local herders and incoming Bantu-speaking farmers," said Emmanuel Ndiema from the National Museums of Kenya, a project partner. "This study exemplifies National Museums of Kenya's commitment to uncovering the deep historical roots of Kenya's agricultural heritage and fostering an appreciation of how past human adaptations can inform future food security and environmental sustainability."
Situated north of Lake Victoria, near the Kenya-Uganda border, Kakapel is recognized as a rock art site with archaeological artifacts reflecting over 9,000 years of human occupation. It has been a Kenyan national monument since 2004.
"Kakapel Rockshelter is one of the only sites in the region where we can see such a long sequence of occupation by so many diverse communities," said Steven T. Goldstein, an anthropological archaeologist at the University of Pittsburgh (WashU PhD '17), the other first author of the study. "Using our innovative approaches to excavation, we have been uniquely able to detect the arrival of domesticated plants and animals into Kenya and study the impacts of these introductions on local environments, human technology, and sociocultural systems."
Mueller joined Goldstein and the National Museums of Kenya for excavations at the Kakapel Rockshelter site in 2018, and their work continues. Mueller leads plant investigations at Kakapel with the Max Planck Institute of Geoanthropology as another project partner.
Mueller used a flotation technique to separate remnants of wild and domesticated plant species from ashes and debris in a hearth excavated at Kakapel. Although this technique is used in many parts of the world, it can be challenging in water-scarce locations, limiting its use in east Africa.
The scientists used direct radiocarbon dating on carbonized seeds to document the arrival of cowpea around 2,300 years ago, concurrent with the use of domesticated cattle in the area. They also found evidence of sorghum arriving from the northeast at least 1,000 years ago and hundreds of finger millet seeds dating back at least 1,000 years. Finger millet, indigenous to eastern Africa, remains an important heritage crop for communities near Kakapel today.
An unusual find was field pea (Pisum), burnt but intact, marking the first evidence of peas in Iron Age eastern Africa. "To our knowledge, this is the only evidence of peas in Iron Age eastern Africa," Mueller said.
The exceptional pea, pictured in the paper, represents a mystery. "The standard peas that we eat in North America were domesticated in the near east," Mueller said. "They were grown in Egypt and probably ended up in east Africa by traveling down the Nile through Sudan, which is also likely how sorghum ended up in east Africa. But there is another kind of pea that was domesticated independently in Ethiopia called the Abyssinian pea, and our sample could be either one!"
Many plant remnants at Kakapel remain unidentified due to a lack of a comprehensive reference collection of east African plants. Mueller is currently working on building such a collection for Tanzania's plants.
"Our work shows that African farming was constantly changing as people migrated, adopted new crops, and abandoned others at a local level," Mueller said. "Prior to European colonialism, community-scale flexibility and decision-making was critical for food security - and it still is in many places."
The study's findings may have implications for various fields, including historical linguistics, plant science, genetics, African history, and domestication studies.
Mueller continues to identify wild plants from the oldest parts of the site, predating agriculture. "This is where human evolution occurred," Mueller said. "This is where hunting and gathering was invented by people at the dawn of time. But there has been no archaeological evidence about which plants hunter-gatherers were eating from this region. If we can get that kind of information from this assemblage, then that is a great contribution."
Research Report:Early agriculture and crop transitions at Kakapel Rockshelter in the Lake Victoria region of eastern Africa
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