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Disease, Biodiversity & the Wealth of Nations

One of the foundational books of modern economics is An Inquiry into the Nature and Causes of the Wealth of Nations by Adam Smith. Smith elaborates on topics ranging from currency to division of labor, and also discusses the oft quoted concept of the "invisible hand" which guides the marketplace to efficient outcomes. According to Smith and many economists, the wealth of nations is primarily derived from political and economic institutions.

But what if that is only part of the equation? It has long been observed that there is a correlation between geography and wealth, namely, countries close to the equator are poor, while countries far from the equator are rich. (See first figure.) 
Geography-GDP.jpg
Several explanations have been proposed, one of which is infectious disease. Countries near the equator must cope with diseases, such as malaria, that countries far from the equator do not. That's because malaria-carrying mosquitoes can survive year round in the tropics, but only thrive seasonally in more temperate climates. With this in mind, is it possible that basic biology is one of the driving forces behind economic growth?

The connection between biology and economics was explored in greater depth in a recent PLoS Biology paper.

One of the difficulties in investigating the cause of economic poverty is that multiple factors simultaneously influence each other. In this case, poverty causes an inability to deal with infectious disease, and a greater burden of disease causes more poverty. Yet, determining how and to what extent disease can directly affect economic outcomes is more than just an academic exercise. It may very well be that providing adequate health care to poor countries is a necessary part of any economic development plan. 

The authors attempted to determine the relationship between disease (specifically parasitic and vector-borne diseases, which are typically endemic) and per capita income. They also examined another crucial factor: The role biodiversity plays in disease burden. To do this, the authors constructed a statistical model which included data on disability due to vector-borne diseases, per capita income, biodiversity, the effectiveness of governing institutions, and various features of geography.

As expected, the authors found that a greater burden of disease correlates with lower per capita income. Perhaps unexpectedly, after controlling for other variables, the authors found that greater biodiversity correlates with a lower disease burden. (See second figure; y-axis represents disease burden.) Presumably, greater biodiversity causes problems for human pathogens. For example, if there are more types of birds around, more malaria-carrying mosquitoes will get eaten. 
Biodiversity-Disease.jpg
Combined, the above findings imply that increasing biodiversity could help increase per capita income.

Additionally, these results suggest that preserving biodiversity -- while a worthy goal in and of itself -- is incredibly relevant to the livelihoods of people. Indeed, a healthier ecosystem may allow for a wealthier planet.

Source: Bonds MH, Dobson AP, Keenan DC (2012). Disease Ecology, Biodiversity, and the Latitudinal Gradient in Income. PLoS Biol 10(12): e1001456. doi:10.1371/journal.pbio.1001456

Source: Disease Burden Links Ecology to Economic Growth (Press Release).

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