A new study published in the Proceedings of the National Academy of Sciences debunks the widely-held conservative notion that early human herders, moving from northern Africa to southern Africa, could not have traveled just east of Lake Victoria in Kenya some 2,000 years ago because the area was bushy, moist and filled with tsetse flies that cause deadly sleeping sickness in livestock and humans.
Young Maasai cattle herder in Kenya, 1979. Image credit: John Atherton / CC BY-SA 2.0.
Once green, the Sahara expanded 5,500 years ago, leading ancient herders to follow the rain and grasslands south to eastern Africa.
But 2,000 years ago, their southward migration stalled out, stopped in its tracks, archaeologists presumed, by tsetse-infested bush and disease.
As the theory goes, the tiny tsetse fly altered the course of history, stopping the spread of domesticated animal herding with a bite that carries sleeping sickness.
Now, the new study on animal remains from a 2,000-year-old settlement near Gogo Falls in Kenya has cast doubt on this idea.
“We studied the chemical signature of teeth in wild antelopes and domestic plant-eating animals – cows and sheep or goats – and found they all were eating a lot of grass in the Lake Victoria Basin. That means Lake Victoria could have been an area through which people passed while migrating southward to southern Africa,” said study lead author Kendra Chritz from the University of Utah.
“The route people took on this southward migration has been a mystery, but recent genetic evidence supports that people moved from east Africa to southern Africa about 2,000 years ago. The specific route out of Kenya has been debated.”
“It was thought that Lake Victoria wasn’t part of the route because of a natural barrier – namely, a cool, moist, bushy environment filled with tsetse flies that would have infected humans and livestock with African sleeping sickness, which can be fatal.”
The people who traveled through western Kenya were known as Elmenteitan herders. They still got some food from hunting, particularly antelope, but they relied 90 percent on their domestic animals for food beginning some 3,000 years ago.
Human genetic evidence indicates they traveled through Kenya’s Great Rift Valley on their way south to the Lake Victoria Basin, which today includes parts of Kenya, Uganda and Tanzania.
Ms Chritz and her colleagues studied fossil teeth of various animals that had been collected at a site on the east side of Lake Victoria known as Gogo Falls, on the Kuja River. Earlier research indicates herders were there less than 2,000 years ago.
They analyzed 86 fossil teeth excavated from the ancient ash of cooking fires at the Gogo Falls site in 1986 and stored at the National Museum of Kenya. The teeth came from caprines, which are sheep or goats and from cows, various species of large and small antelopes, zebras, hippos, warthogs and bushpigs.
To avoid damaging the teeth, they removed only 1-mg samples of tooth enamel from already broken tooth edges.
They then determined the ratios of heavier, rarer carbon-13 to lighter, common carbon-12. Those carbon-isotope ratios indicate whether an animal ate what are called C3 plants, which include leafy trees, shrubs, forbs and herbs, or C4 plants, which include grasses and sedges. Higher carbon-13-to-carbon-12 ratios indicate a C4 grassy diet.
The results indicate that at Gogo Falls, the cows and sheep or goats – as well as the majority of wild animals – ate a grassy diet.
“That is consistent with studies of old pollen and leaf wax from lake sediments that also suggested the Lake Victoria Basin had a grassy landscape,” Ms Chritz said.
The team found that 10 of the 13 species of wild and domestic animals ate a diet of more than 80 percent grass – cows and caprines ate almost a pure grass diet – while bush pigs and large and small forest antelopes ate less than 80 percent grass, but still far more than in a modern environment.
“It isn’t necessarily true that grasslands near Lake Victoria developed naturally and attracted herders, but that it may have been the other way around.”
“They may have maintained the environment to keep it grassy by using grazing – as the Maasai people do today in southwest Kenya and northern Tanzania – and/or with fire.”
“The area around Lake Victoria is much different today than it was 2,000 years ago, largely due to overgrazing of grasses by livestock and to increasing bushiness as humans kill or relocate giraffes and elephants in the area.”
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Kendra L. Chritz et al. Environments and trypanosomiasis risks for early herders in the later Holocene of the Lake Victoria basin, Kenya. PNAS, published online March 9, 2015; doi: 10.1073/pnas.1423953112
