In this book, noted biologist Eric Charnov uses ideas about symmetry, invariance, and scaling laws to explain many formerly puzzling regularities in population biology. Aspects of life history evolution and population dynamics are illuminated by his synthesis of symmetry and symmetry-breaking arguments. For example, he develops sex allocation evolution to reveal how symmetry-breaking leads to biased sex ratios, and also demonstrates how the process plays an important role in the evolution of alternative male life histories. A detailed evolutionary theory is developed and tested for the allometric structure of life histories in female mammals. The symmetry perspective is also applied to studies of aging as well as to the study of allometry in population dynamics. This work will attract interest among a wide range of students and researchers in ecology, evolution, behavior, and other fields within organismal biology.