Scientists widely believe that Saharan history was altered by the disease-carrying tsetse fly, but new research suggests this might not be the case after all.
The Sahara desert expanded in about 5,500, causing herders to move south in search of wetter land, but about 2,000 years ago this expansion suddenly stopped. Researchers believed the migration subsided because herds of cattle and their handlers were being killed off by the tsetse fly, which carries fatal diseases such as carries sleeping sickness and nagana, Washington University in St. Louis reported. New isotopic research conducted on animal remains from a nearly 2,000-year-old settlement in Kenya's Gogo Falls suggests otherwise.
"This study overturns previous assumptions about environmental constraints on livestock management in a key area for southward movement of early herders," said study co-author Fiona Marshall, professor of anthropology at Washington University. "It reveals that the vegetation east of Lake Victoria was then much different than it is today and that ancient grassy environments may have provided an important corridor for herders moving into southern Africa."
The isotopic analysis on tooth enamel of both domestic and wild herbivores from this region revealed they feasted on lush vegetation, making it unlikely the tsetse fly was prevalent. The evidence of fertile land in the region also suggests the use of both domestic and wild food sources was likely a choice, rather than a necessity.
"Our findings challenge existing models that explain the settlement's diverse diet as a consequence of depressed livestock production related to tsetse flies," Marshall said. "Instead of this ecological explanation, our isotopic findings support the notion that herders may simply have interacted with hunter-gatherer groups already living in these areas, adapting to their foraging styles. This suggests that social factors may have played a greater role than previously thought in subsistence diversity during the spread of pastoralism in Eastern Africa."
Scientists have had trouble finding physical archaeological evidence of these early pastoral migrations, but recent genetic analyses of descendants of southern African peoples revealed the prevalence of an early mutation for lactase persistence. This genetic trait makes one more likely to be able to stomach non-human milk, and those without the mutation are more likely to be lactose intolerant. This trait is believed to have developed in southern Africa thousands of years ago, suggesting herders had arrived in these regions earlier than was previously estimated.
"Herding was the earliest form of African food production and it transformed the lives of local populations of people and animals," Marshall said. "The research offers new insight into the role that tsetse flies and bushy environments played in depressing livestock production and human disease, suggesting that grassland distributions in the Lake Victoria basin were not similar those of today and that barriers to the southward spread of pastoralism fluctuated more than previously thought."
The findings provide insights into key factors that influenced the modern distribution of populations of both people and animals.
The study was published in a recent edition of the journal Proceedings of the National Academy of Sciences.
