The tropics: What a great place for a vacation, what a terrible place to live. According to the United Nations and the International Monetary Fund, respectively, they’re home to 41 of the world’s “least developed countries” and only two of the world’s 34 “advanced economies.” The tropics, as they say, can’t win for losing.
What’s more, says the UN, the tropics are a sunny, sweaty playground for some 93 percent of the world’s vector-borne and parasitic diseases (VBPD). That disease and deprivation coexist in the tropics isn’t a coincidence. As suggested in a new study by researchers from Harvard, Princeton, and the University of Cergy-Pontoise in France, the abysmal disease situation in the tropics has a direct and persistent bearing on why income tends to decrease the closer you get to the equator.
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That may seem obvious at first blush. But the chicken-egg relationship between disease levels and economy has long been debated.
Ever since European civilizations first made it their business to kill, conquer and exploit their neighbors to the south, the link between latitude and a society’s ability to control its own economic destiny has seemed so obvious as to be taken for granted. Over the years, numerous reasons have been offered to explain that general pattern. Some were racist, others were colonialist, and others still were at least Orientalist, however unwittingly-intentioned.
More contemporary theories, the authors of the new study note, have begun to incorporate the constraining, inhibiting effects of biophysical factors like disease in their analyses of why the tropics struggle so much. Of course, disease exists everywhere. But disease may play a special, a priori role in the tropics, the authors note, because of the nature of the diseases themselves:
VBPDs continue to be among the leading causes of morbidity and mortality of poor populations. Unlike directly transmitted diseases, VBPDs spend much of their life cycle outside of the human host, in other host species or in free-living stages, and are thus especially dependent on external environmental conditions. There is now a consensus among many economists that at least some VBPDS, such as malaria and hookworm, have systematically influenced economic growth.
The extent and manner of the role VBPDs play in those economies is a matter of debate among economists and scientists. On one hand, the study notes, disease may work in tandem with agricultural conditions that are more inferior overall, both of which influence the health of a country and, hence, its human capital labor productivity.
The graph on the left shows how much less you can expect to live in the tropics (measured in disability-adjusted life years). The one on the right shows you how poor you’ll be while losing years off your life. Graph taken from the report, in the journal PLOS Biology
On the other hand, an historical perspective argues that the kinds of economic structures typically found in more prosperous countries (a system of individual property rights, for example) were never allowed to flourish in equatorial countries because the European colonizers settling there could never stay disease-free long enough to put down roots. They chose, instead, to simply pillage for all it was worth and get out, never reinvesting, handicapping those countries’ abilities to ever piece together a viable, post-colonial company.
The problem with this analysis, the new study’s authors note, is it neglects the continued detrimental effects of disease today.
In either case, it has been difficult to disentangle the direct effects of disease, since economic factors created by poor agriculture, poor government, or a lack of cohesive civil society can also have a direct influence on health: Put simply, if a society can’t feed its people, drain its swamps and administer the meds, it’s people will get sick.
This new study—published today in the open access journal PLOS Biology—manages, to some extent, to sort the chicken from the egg—an important task in practical terms, it’s authors note, because “If health is a fundamental ingredient of economic growth, then health care and nutrition would be essential components of macroeconomic strategies for poor countries, and would also be justified targets of foreign economic aid.”
After controlling for multiple social, economic and biophysical factors, the researchers were able to more or less isolate the effects of VBPDs to determine a “substantial and statistically significant impact” of such diseases on per capita income. “Infectious and parasitic diseases effectively ‘steal’ host resources for their own survival and transmission,” they note.
Among the more interesting variables the researchers found to be influencing what they call the “burden of VBPDs,” is biodiversity. Specifically, they found that the more biodiversity is attributed to a given area, the lower that area’s VBPD burden will be.
Causation there is still unclear, as the study’s authors admit more research will have to be done. But the implication is stark: As climate change and human expansion threatens and eradicates more and more species, these tropical areas — already increasingly threatened by droughts and, in many cases, rising sea levels — face another, indirect menace to their prosperity. Add it to the list of reasons to bike more and use a condom.
