In the 150 years since Darwin, the field of evolutionary biology has left a glaring gap in understanding how animals developed their astounding variety and complexity. The standard answer has been that small genetic mutations accumulate over time to produce wondrous innovations such as eyes and wings. Drawing on cutting-edge research across the spectrum of modern biology, Marc Kirschner and John Gerhart demonstrate how this stock answer is woefully inadequate. Rather they offer an original solution to the longstanding puzzle of how small random genetic change can be converted into complex, useful innovations. In a new theory they call "facilitated variation,” Kirschner and Gerhart elevate the individual organism from a passive target of natural selection to a central player in the 3-billion-year history of evolution. In clear, accessible language, the authors invite every reader to contemplate daring new ideas about evolution. By closing the major gap in Darwin’s theory Kirschner and Gerhart also provide a timely scientific rebuttal to modern critics of evolution who champion "intelligent design.”

These original contributions by symbiosis biologists and evolutionary theorists address the adequacy of the prevailing neo-Darwinian concept of evolution in the light of growing evidence that hereditary symbiosis, supplemented by the gradual accumulation of heritable mutation, results in the origin of new species and morphological novelty. A departure from mainstream biology, the idea of symbiosis—as in the genetic and metabolic interactions of the bacterial communities that became the earliest eukaryotes and eventually evolved into plants and animals—has attracted the attention of a growing number of scientists. These original contributions by symbiosis biologists and evolutionary theorists address the adequacy of the prevailing neo-Darwinian concept of evolution in the light of growing evidence that hereditary symbiosis, supplemented by the gradual accumulation of heritable mutation, results in the origin of new species and morphological novelty. They include reports of current research on the evolutionary consequences of symbiosis, the protracted physical association between organisms of different species. Among the issues considered are individuality and evolution, microbial symbioses, animal­bacterial symbioses, and the importance of symbiosis in cell evolution, ecology, and morphogenesis. Lynn Margulis, Distinguished Professor of Botany at the University of Massachusetts at Amherst, is the modern originator of the symbiotic theory of cell evolution. Once considered heresy, her ideas are now part of the microbiological revolution. Contributors Peter Atsatt, Richard C. Back, David Bermudes, Paola Bonfante-Fasolo, René Fester, Lynda J. Goff, Anne-Marie Grenier, Ricardo Guerrero, Robert H. Haynes, Rosmarie Honegger, Gregory Hinkle, Kwang W. Jeon, Bryce Kendrick, Richard Law, David Lewis, Lynn Margulis, John Maynard Smith, Margaret J. McFall-Ngai, Paul Nardon, Kenneth H. Nealson, Kris Pirozynski, Peter W. Price, Mary Beth Saffo, Jan Sapp, Silvano Scannerini, Werner Schwemmler, Sorin Sonea, Toomas H. Tiivel, Robert K. Trench, Russell Vetter