Chad is dirt poor because its dirt is poor. Germany is relatively rich because its soil is rich. That’s the provocative conclusion flowing from a new study, which suggests that just two fundamental factors—soil type and climate—can largely explain why humans have prospered in some places but not in others. The finding, drawn from a computer model originally used to predict the distribution of moths, also may help explain why some regions are more prone to violence than others.
Since at least the 1700s, scholars have argued that geographic differences such as rainfall, air temperature, and soil quality can have a major impact on economic development. They noted that many poor nations, for instance, are clustered in tropical regions characterized by poor soils for agriculture and lots of nasty diseases, such as malaria. More recently, scholars such as best-selling geographer Jared Diamond of the University of California, Los Angeles, have also suggested that regions that didn’t have easily domesticated animals, such as central Africa, ultimately became less wealthy than those that did. Critics of “biogeographical determinism,” however, have argued that other factors—such as a people’s history, culture, and educational and political institutions—better explain why nations in cooler regions have prospered.
Jan Beck, an insect ecologist at the University of Basel in Switzerland, found himself in the middle of this debate a few years ago while leading his students on a field trip in Ethiopia. One night, he pointed out that the nation’s population and wealth seemed to vary by rainfall and soil type, with prosperous settlements clumped in wetter, more fertile regions. Some of the students challenged that notion, arguing that history and culture had also played a role. Later, Beck and Andrea Sieber, one of the students, began to explore how far they could take the issue. “We wanted to see if you could use a very simple environmental model to predict how humans use the landscape,” says Beck, whose specialty is studying moths.
To tackle their simulation, the pair turned to computer models originally developed by ecologists to predict an animal’s geographic range. By looking at variables such as day and night temperatures and seasonal rainfall and vegetation types, for instance, researchers can identify the ecological niches best suited to certain insects. For their study, Beck and Sieber selected 19 climate and soil variables that could influence how humans use the land, including soil type and precipitation in the coldest and warmest seasons. Then, they calculated how well those variables predicted four common modes of human land use in Asia, Africa, Europe, and Australia: farming, sedentary animal husbandry, nomadic wandering, and hunting and gathering.
The resulting maps, which appear in PLoS ONE, “were pretty surprising,” says Beck. “Using just those two factors, climate and soils, we were able to predict human land use fairly reliably.” The maps confirmed, for instance, that areas fertile enough for crop farming are able to support much denser and richer populations than regions more suited to ranching or hunting. Much of Europe turned out to have a relatively farming-friendly climate and landscape, perhaps explaining why it has prospered. The model also identified how environmental factors might contribute to human conflicts by making land open to multiple uses. In large chunks of Africa, for instance, it suggested the landscape could support two competing uses: agriculture and nomadic pastoralism. Some of those same regions, Beck notes, are today rife with violence, sometimes related to conflicts over resources.
Beck is careful to note that his relatively simple model failed to correctly predict present land uses up to one-third of the time, suggesting history and culture do influence how humans use the land. The maps “help identify those places where environmental conditions alone don’t explain everything,” he says, and help focus attention on other factors—such as past political or economic developments—that may have shaped present practices.
Beck’s approach is “interesting and useful,” but it has some significant weaknesses, says economist John Bluedorn of the University of Southampton in the United Kingdom. One problem is that “there is no recognition that historic climate and soil types may be quite different from today's local climate and soil types.” And he cautions that policymakers shouldn’t read too much into the study. The idea that “if geography is destiny, then drives to reduce global poverty ... are doomed to fail” is not supported by experience, he says.
The model also fails to fully account for the dramatic technological, economic, and demographic trends that have swept the world over the past century, says economist Holger Strulik, a visiting professor at Brown University. Good agricultural soils and high population densities are no longer the best predictors “for economic power,” he says. Germany, for instance, has largely abandoned agriculture but remains an economic heavyweight. The new study would be on firmer ground, he believes, if it had looked at how soil and climate influenced development up to about the year 1500 and stopped there.
*This has article has been corrected. Due to an editing error, the image caption previously referred to (red, left) and (red, right).