Joel E. Cohen is the Abby Rockefeller Mauzé Professor of Populations at the Rockefeller University, New York. He heads the Laboratory of Populations at the Rockefeller and Columbia Universities. At Columbia University, New York, he is Professor of Populations in the Earth Institute, with appointments in the Departments of International and Public Affairs; Earth and Environmental Sciences; and Ecology, Evolution, and Environmental Biology. Martin B. Malin is the Executive Director of the Managing the Atom Project at the Kennedy School of Government of Harvard University. He is a former Program Director at the American Academy of Arts and Sciences.   About the American Academy of Arts & Sciences Founded in 1780, the American Academy of Arts and Sciences is an independent policy research center that conducts multidisciplinary studies of complex and emerging problems. Current Academy research focuses on: science and global security; social policy; the humanities and culture; and education. With headquarters in Cambridge, Massachusetts, the Academy’s work is advanced by its 4,600 elected members, who are leaders in the academic disciplines, the arts, business and public affairs from around the world.