In the twentieth century, scientists in the relatively new field of biology played an important role in exposing the threats of environmental degradation, loss of species diversity, habitat fragmentation, scarce energy resources, and human population growth. In the essays found in this volume, some of the world's most notable biologists consider how their discipline must evolve to address these problems in the twenty-first century. Contributors include: Gary W. Barrett, Daniel H. Janzen, W. John Kress, Gene Likens, Thomas E. Lovejoy, Lynn Margulis, Ernst Mayr, Gordon H. Orians, Ghillean T. Pearce, Marvalee Wake, and Edward O. Wilson.