This chapter examines the nature of farmer selection using material from research on wheat diversity in Turkey. It discusses how the application of Mendelian genetics to crop improvement, coupled with the rise of industrial processes, and markets for agricultural inputs, has radically changed the context and nature of crop evolution. Nevertheless, agricultural development, like other human patterns, involves both linear and nonlinear processes. Linear processes include the dispersal of human ideas and technology, and increasing specialization and integration, and have predictable effects on crop evolution and diversity. Non-linear processes include cultural resistance to dispersal, the balancing of tradeoffs between competing goals, and the obstacles arising in habitats that are spatially structured by environmental and social heterogeneity. The result is that breeder-based crop evolution has become an important but not an inevitably hegemonic force in the future of crop ecology in centers of diversity.