This volume 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 the synthesis of symmetry and symmetry-breaking arguments. For example, sex allocation evolution is developed to reveal how symmetry-breaking leads to biased sex ratios, and demonstrates how symmetry-breaking plays an important role in the evolution of alternative male life histories. Symmetry appears in many other life history problems. Here it is discussed in terms of the phylogenetic invariance of certain dimensionless numbers derived from birth, death and growth rates. 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 ageing, where novel hypotheses are developed for determinate versus indeterminate growers, sex-changing fish and pollen grains. Finally, symmetry arguments are used to explore allometry in population dynamics. Eric Charnov is the author of "The Theory of Sex Allocation" and co-author of "Infant-Mother Attachment".