Natural selection can occur in any system whose members have the properties of variation, replication, and heredity. In the hierarchy of biological organization, which ranges from cells and gametes to populations and species, selection can and does operate simultaneously at more than one level and in more than one direction. As a result, the genetic response to selection can be quantitatively and qualitatively different at different levels because the levels differ in the nature of replication and hereditary material. The proposed work will synthesize more than thirty years of theoretical, experimental and field research conducted with students on levels of selection. The book will focus especially on genetic interactions and the effectiveness of different kinds of selection. The synthesis will be published as a professional monograph and, on the web, as materials for use in graduate and advanced undergraduate courses. Gene interactions play an important role in reproductive isolation between species, inbreeding depression, and in both complex adaptations and diseases. However, much of population genetic theory is based on models of single genes. This will be the first synthesis of this large body of research.
