Dr. Cohen and his colleagues combine mathematical tools with observations of concrete problems in demography, epidemiology, and ecology to better understand populations. His research spans studies of human population growth, infectious diseases and food webs.

A major challenge in the coming decades is to understand how demographic, economic and cultural changes will interact with Earth’s physical, chemical and biological environments. Dr. Cohen’s laboratory has analyzed the spatial distribution of Earth’s human population in relation to geophysical factors such as elevation, distance from coasts or navigable rivers, temperature and precipitation. As neutral experts for federal courts, Dr. Cohen and his colleagues developed and used methods to predict future claimants of asbestos-related diseases and injuries. Their methods may provide models for future mass-tort litigation as well as for long-term assessments of the impact of other environmental contaminants.

Dr. Cohen also studies Chagas disease, an insect-borne infectious disease that is a New World relative of African sleeping sickness. Chronic Chagas disease afflicts millions of people in Latin America and has no cure. Dr. Cohen collaborates with Argentine colleagues in a field study of the control of Chagas disease in rural northwest Argentina. They have developed a mathematical model of the risk of household transmission to humans, which enables the indigenous population to improve disease control by better household management.

Because ecological communities strongly affect human well-being, Dr. Cohen’s research extends to nonhuman species as well. One approach focuses on a food web, a flowchart of who eats whom that describes the major pathways of food energy and of chemical and biological toxins. Dr. Cohen and colleagues developed a new food web graph, which plots species and feeding links in the plane spanned by species’ average body mass and numerical abundance. They analyzed unique data on soil food webs at 146 sites in the Netherlands to understand how environmental variables, human land uses and below-ground food webs interact.

Dr. Cohen’s laboratory also studies fundamental questions in the biology of aging. His colleagues quantitatively analyze age patterns of senescence-related variables, including total and cause-specific rates of mortality, morbidity and disability, as well as biomarkers of aging. They have found that variations in age trajectories reflect underlying mechanisms of senescence, evolutionary backgrounds of the mechanisms, senescence-disease relationships and environmental and genetic effects on senescence.

The laboratory also seeks to understand how stochasticity — random influences such as changes in weather or resources, or chance events of birth and death — creates novel patterns in non-linear dynamics of population change. Dr. Cohen and his colleagues studied contained populations of flour beetles, cannibalistic insects that have long been used to study population dynamics. From time series of counts of the numbers of larvae, pupae and adults in jars, the researchers derived “power spectra” to compare the accuracy of predictions about the beetle population generated by their model with the accuracy of predictions generated using the linearization methods from physics, a more traditional means of understanding randomly perturbed dynamical systems. In most cases, predictions of their model were far more successful in describing the experimental data.

CAREER

Dr. Cohen earned his B.A., summa cum laude, from Harvard University in 1965. He holds two doctoral degrees from Harvard, a Ph.D. in applied mathematics (1970) and a doctor of public health in population sciences and tropical public health (1973). He taught at Harvard from 1971 until his appointment as professor at The Rockefeller University in 1975.

Dr. Cohen was a MacArthur Foundation Fellow and is a member of the National Academy of Sciences, the board of directors of The Nature Conservancy and the board of trustees of the Population Reference Bureau. He shared the Tyler Prize for Environmental Achievement in 1999 and the Fred L. Soper Prize of the Pan American Health Organization, Washington, DC, in 1998 for work on Chagas disease.