For more than five decades, Paul R. Ehrlich has been alerting people to the importance of ecological threats, including overpopulation, natural resource depletion, loss of biodiversity, climate change, and nuclear winter. His frequent appearances in the news media, along with his many popular books, have made him a household name among environmentally minded Americans—and a lightning rod for attacks by conservatives who do not share his views on the environment or politics. Although he began his career as an entomologist, much of Ehrlich’s work now focuses on the interactions between one species—Homo sapiens—and the rest of the natural world. His latest project is an interdisciplinary proposal that marries the natural sciences with the social sciences in an attempt to understand human behavior—and how to change it for the better. In this interview, Ehrlich explains the vision for the Millennium Alliance for Humanity and the Biosphere and why he believes that the social sciences can make an essential contribution to addressing problems such as climate change. He argues that a vast “culture gap” prevents modern humans from grasping scientific concepts essential to our survival. He points out that even the news media has failed to understand the non-linearity of population impacts, in which each new increment of population growth does more environmental damage than the same increment added in an earlier time. And he warns that the risk of nuclear winter, even from a “small” nuclear war, is as real as ever.