AWARDEES: Joel E. Cohen & Christopher Small

SCIENCE: Hypsographic Demography

FEDERAL FUNDING AGENCY: National Science Foundation

What is a mathematical population biologist? What work might one do with a geophysicist? And why are cancer researchers, the public health sector, and companies like Frito-Lay, Procter & Gamble, and Intel happy they came together? Meet Joel E. Cohen, the mathematical population biologist, and Christopher Small, the geophysicist. Their obscure, curiosity-driven research on “hypsographic demography”—the study of how human populations are distributed with respect to altitude—has provided crucial insights in areas as diverse as food production and packaging, semiconductor manufacturing, and biomedical research and development.

Supported by funding from the National Science Foundation (NSF) and the University Corporation for Atmospheric Research (UCAR)—which receives the majority of its funding from NSF and other federal research agencies—Cohen and Small brought their disparate areas of expertise together to pursue a shared curiosity: how many people live at any given altitude on Earth and how are they distributed? At the time they were thinking particularly about people living near sea level, who could be at risk from flooding and other coastal disasters. The broader impact of their work has been a complete and gratifying surprise, not only for the researchers themselves, but also for the many unexpected beneficiaries.

Their path together began in New York in 1996, when Joel Cohen traveled across town from his home institution, Rockefeller University, to Columbia University. He was there to give a talk about his work on “chaotic non-linear population models,” but he had been bothered for some time by another thought. Then as now, much of Cohen’s work focused on what are called food webs, the more sophisticated cousin of the food chains most of us learned about in school. He had come to realize that in his decades of studying biological populations, he had, in his words, been studying “actors on a stage without knowing anything about the stage itself!"

Christopher Small was then a young researcher at Columbia’s Lamont-Doherty Earth Observatory (LDEO) who had finished his PhD a few years prior. That day in 1996, he made the fortuitous decision to take a break from his own research to attend Cohen’s seemingly unrelated talk on population models. The two talked afterwards, and within a few hours had found their curiosities covered a lot of common ground, so they decided to collaborate in their research. Small helped Cohen secure a visiting position at LDEO to facilitate their work. At this point, however, just what they would do together was unclear.

At the time, Small received support from NSF to study the structure of the sea floor and the formation of the world’s undersea volcanoes. He and his former PhD advisor had been working to combine new maps of the sea floor and Earth’s land surface into a fully global digital map, from the bottom of the sea floor to the top of Mount Everest. Over the course of a few summers, Small shared his growing insights about the Earth with Cohen as he learned about populations.

A year earlier, in 1995, Waldo Tobler, a geographer and cartographer, and his collaborators had produced the first gridded model of the human population with support from NSF and NASA. Whereas population maps prior to that time were “political”—based on the boundaries of nations, states, cities, and districts—this new global population map was on a standardized grid that ignored political boundaries.

Spurred by the Tobler team’s new population map, Cohen and Small began to wonder about many unanswered questions at the intersection of earth and population sciences, and about how different kinds of maps might be combined to address them. To this excellent example of interdisciplinary collaboration, Small brought his understanding of the Earth—the stage—and Cohen his knowledge of human and other biological populations—the actors. They narrowed in on one question in particular: how many people live at low elevations in coastal areas where they might be at risk due to flooding and other natural disasters?

In no small technical feat, they combined the new gridded population model with the new global digital map of Earth altitudes to produce their global model of hypsographic demography (“hypso” being the Greek word for height and “demos” Greek for people). With their model, Cohen and Small showed that, based on 1994 census estimates, over one-third of the world’s population lived within 300 feet of sea level. Unexpectedly, they found that most of those people lived not in familiar, large cities like New York, Miami, and Los Angeles, but in areas with lower population density—a discovery with important consequences for disaster preparedness and other policy issues.  

With crucial support from UCAR, Cohen and Small used a variety of tools to extend their analysis of challenges for populations at low altitude. But food giant Frito-Lay saw even further potential, giving Small “the biggest surprise of his scientific career” when the company contacted him to express interest in the research. Frito-Lay was trying to determine if there were significant markets for its products among populations at high altitudes. If so, it would need to develop packaging strong enough to withstand potentially big differences in air pressures between where products were manufactured and the high-altitude locations to which they would be shipped. Frito-Lay even provided Small with follow-on research funding to extend their original work to produce a more detailed view of populations living at high altitudes in mountain ranges worldwide.

Since then the pair have fielded inquiries about their work from a number of companies, including Proctor & Gamble, whose soaps form and mix bubbles differently at different altitudes, and Intel, whose microchips cool more or less efficiently at different altitudes. In fact, Cohen and Small’s hypsographic demography research informs standards important to the cooling of microchips in today’s personal computers.

An astoundingly broad range of research articles cite Cohen and Small’s groundbreaking 1998 paper debuting hypsographic demography. The topics of these papers range from issues in ecology and biodiversity to modern LED lighting systems, and they include a plethora of studies in the biomedical sciences. In fact, Cohen subsequently worked alongside cancer researchers studying a rare tumor that is more likely to form in humans living at high altitude due to mild oxygen deprivation. Cohen and Small’s work helps those researchers and public health professionals better identify and support at-risk populations and study the mechanisms of disease.

Some might wonder why the National Science Foundation and UCAR would have spent scarce research dollars to fund a mathematical population biologist to spend summers studying earth science or for an earth scientist to work on biological populations. But the far-reaching implications of this curiosity-driven research stand as a strong testament to an insight by Dr. Cohen himself: "Pursue something beautiful and true, and often it will prove useful." 


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