Joel E. Cohen

Populations exhibit phenomena that are difficult to deduce from the characteristics of any member. A population's prevalence of disease is only indirectly connected to the course of disease in an individual; outcomes preferred by all individuals in a society may be attainable only when individuals cooperate or coordinate their behavior with the behavior of others. To develop concepts and theories helpful for understanding human and nonhuman populations, I have studied problems in demography, epidemiology, ecology, and social behavior using tools of mathematics, computation, and statistics. In demography, I studied the uncertainty of population projections theoretically and in practical applications ranging from striped bass in Chesapeake Bay to asbestos-related diseases of humans. I studied how many people the Earth can support. I found that population, economics, the environment, and culture all interact strongly to influence trade-offs in human well-being. In epidemiology, I developed mathematical models of malaria, schistosomiasis, and American trypanosomiasis to suggest improved interventions. In ecology, I studied food webs, which tell who eats whom in an ecological community. I proposed concepts and models to interpret food web structures and tested these models with observations from natural systems and agricultural rice fields. My mathematical studies, prompted by questions about populations, concerned eigenvalue inequalities, products of random matrices, random graphs, relative entropy, nonlinear mappings, queuing networks, and game theory.