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Marcella Alsan on the tsetse fly’s lasting impacts on African development

Barefoot teenagers on a rough stony road cart a heavy load of bananas to the market

Two boys are transporting a hefty load — approximately 265 pounds of bananas  — on a wooden bicycle from the small village of Kibati into the town of Goma in Congo.

Oct 29 2015

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Featured Scholars

Marcella Alsan, Assistant Professor of Medicine at Stanford and a SCID Faculty Affiliate, has found her vocation as a physician/economist working at the intersection of global economics and health. Her research on the tsetse fly and development, published in 2015 in the American Economic Review, has drawn wide attention, including an article in The Economist that carried the subhead “How an insect held back a continent.”

Like mosquitoes that carry malaria and fleas that spread plague and typhus, the tsetse fly has changed the course of history. The tsetse is the carrier of the disease trypanosomiasis, better known as sleeping sickness, which every year kills thousands of people. But the fly’s most deadly effects have been on livestock. The animal form of sleeping sickness, called nagana, is more widespread and lethal than the human form, and has kept domesticated species such as horses and cattle from thriving in vast parts of Africa. It’s long been speculated that the tsetse explains the absence of draft animals and plows in large parts of Africa, which forced many populations to use far less productive technologies, like the hoe.

To investigate the role of tsetse, Alsan designed a “tsetse suitability index” measuring how favorable an area’s climate is for the fly, and assessing the tsetse’s historical prevalence in the homelands of hundreds of African ethnic groups. She found that the higher an area’s index reading, the less likely it was that the people who lived there kept large domesticated animals, practiced intensive agriculture, used plows, or densely settled the territory. “The tsetse fly had an important impact on the diffusion of agricultural technologies and the generation of agricultural surplus in many parts of Africa,” she explains. In addition, groups in territories with high scores were more likely to keep slaves, perhaps because, in the absence of animal power, they needed human labor. Such patterns didn’t occur in regions outside Africa that had similar climates, suggesting that it was the presence of the tsetse that helps explain underdevelopment in the fly’s territory.

Alsan finds evidence that the suitability of an area to the tsetse fly is associated not only with economic impacts, but also political ones. High index readings corresponded to areas that were less likely to have centralized political institutions, such as kingdoms. In the absence of a strong central authority commanding resources, economic development may have been further hindered.

The impacts of the tsetse fly on economic and political development are likely to persist over time, Alsan concludes. Using data collected by satellites, she observed that artificial light is sparse in regions suitable for the tsetse, indicating lower levels of economic development. She interprets this relative backwardness as a legacy of political systems kept decentralized by the tsetse fly. She also found fewer cattle in these regions, evidence that the fly remains an obstacle to economic progress today.

Alsan remains committed to investigating the social and political forces that shape patterns of health and illness around the world. Her research ranges widely. In addition to the tsetse fly, she has studied water, sewerage and infant mortality in Boston; how vaccination campaigns in Turkey affect educational opportunities for girls; the reasons why some HIV-positive patients in Atlanta don’t stick with their treatment plans; and how improved educational opportunities for Ugandan women lowered AIDS risk. Economics, she says, is “a way to drill down into societal problems and come up with solutions, using math, using theory, using data.”