Economics as an Evolutionary Science integrates economics and evolution to produce a social science that is rigorous, internally coherent, testable, and consistent with the natural sciences. The authors suggest an expanded definition of "fitness," emphasizing not only the importance of reproduction and the quality of offspring, but also taking into account the unique ability of human beings to provide material wealth to their children. The book offers a coherent explanation for the recent decline in fertility, which is shown to be consistent with the evolutionary goal of maximizing genetic success. In addition the authors demonstrate the relevance to economics of several core concepts derived from biologists, including the genetics of parent-offspring conflict, inclusive fitness theory, and the phenomena of R-selection and K-selection. The keystone of their presentation is