Ecological diversity has a complicated relationship to health and illness. On the one hand, those parts of the world that are rich in organisms are also rich in disease-causing organisms. On the other hand, as biodiversity declines, the burden of disease increases because organisms that hold pathogens and disease vectors in check are weakened. This is a serious concern because of both anthropogenic climate change and the effects of industrial agriculture.
Ecologies are most diverse near the equator. As you move North and South from the equator—that is, as your latitude increases—ecologies become simpler. As a consequence, the incidence of infectious and parasitic disease is greatest near the equator. This is referred to as a latitudinal gradient.
There’s also a latitudinal gradient in income. As you travel further from the equator, incomes are greater.
An obvious question is whether these three latitudinal gradients are related to one another. A subtler question is how our understanding of these gradients can help us improve our health.
A recent study in the Public Library of Science Biology found that there is a strong relationship between biodiversity, disease, and poverty. The most striking is that, if one accounts for actual regions, latitude ceases to be a factor in how income affects disease. It also ceases to be a factor in how disease affects income.
For example, looking at regions rather than latitudes, people in equatorial Africa have a dramatically higher rate of disease while people in Latin America have a modestly lower rate of disease after taking income and biodiversity into account.
Even more interesting, the degree of biodiversity has a small but significant positive effect in lowering disease rates—that is, areas with greater biodiversity and similar incomes have slightly better health. Not surprisingly, increased income decreases disease rates modestly, while decreased rates of disease increases incomes significantly. That is, eliminating poverty makes people healthier and protecting people’s health improves their income.
As I’m sure you know, former colonies are located close to the equator. As I’m sure you also know, the latitudinal gradients in disease and income have been used as evidence of inferiority—less explicitly now than in the late Nineteenth and early Twentieth Centuries, but still very much in the air. We didn’t need this study to tell us that such ideas are nonsense—as well as chauvinistic and frequently racist.
As so often happens, the latitudinal gradients are dramatic distractions. They look like something is going on, but it’s not.
Instead what we’re left with is the understanding that biodiversity has a positive effect on health and so does the elimination of poverty—wherever you live.