This chapter explores three more examples that all arise in the context of fundamental ecological and evolutionary questions to further illustrate the diversifying force of frequency-dependent interactions. The first example concerns the dynamics of spatially structured populations and serves as an excellent case study for illustrating the feedback between ecological and evolutionary dynamics. The second example concerns the evolution of asymmetry in gamete size between the sexes, which sets the stage for the “paradox of sex.” Finally, the third example concerns the fundamental question of the evolution of trophic levels in food webs, that is, the evolution of complexity in ecosystems.