BOOKS ET AL.

stag might fi ght to death over a ter-ritory or concede it uncontested to another. Neighboring trees invest varying amounts of energy into growth, with the tallest blocking sunlight to others. Viruses infecting a common cell can either make all proteins required for their reproduction or free ride on those made by others. How does evolution shape the strategic phenotype of organisms in life-and-death contests? Such questions fall within the domain of evolutionary game theory, a field that combines strategic concerns with the fun-damental principles of evolution. A game is a simple way to represent interactions. Players choose from a set of possible strategies; for exam-ple, fight or retreat, cooper-ate or defect. The results are recorded as payoffs received by each player. The basic idea of evolutionary game theory is to link payoff to reproductive success ( 1). Thus, a successful strategy will increase in abun-dance over generations as it is successively transmitted from parent to off-spring. Evolutionary game theory applies whenever fitness depends on the pheno-types or actions of others; the fi tness land-scape changes as the population explores it ( 2). The resulting evolutionary dynamics can lead to dominance of a single strategy, coexistence of multiple strategies, periodic cycling, or even chaos ( 3). In its first decades, evolutionary game theory focused primarily on notions of evo-lutionary stability and deterministic dynam-ics. Previous textbooks ( 3 – 6) concentrated on these early themes. However, the scope of evolutionary game theory is rapidly expand-ing—both in terms of the range of situations considered and the variety of underlying models of evolution. Mark Broom and Jan Rychtář’s Game-Theoretical Models in Biol-ogy provides a comprehensive, up-to-date introduction that uniquely blends mathemati-cal clarity and biological intuition