Theoretical perspectives on rapid evolutionary change

Rapid evolutionary change is a common outcome of strong phenotypic selection—from exposure to unusual temperatures to attack by unfamiliar parasites to growth on new food resources—organisms evolve rapidly under challenging circumstances as long as the requisite genetic variation is present. As recounted throughout this book, revolutionary changes in sequencing technology and bioinformatics have allowed biologists to develop a detailed understanding of the genetic basis of rapid evolutionary change from a variety of case studies, from antibiotic resistance to evolutionary responses to sexual conflict. This chapter explores the theoretical implications of strong selection. Much of basic evolutionary theory assumes weak selection acting on a gene; here we will ask when and to what extent strong selection would alter our theoretical predictions. To begin, we must address the issue that strong selection at the phenotypic level need not generate strong selection at the genic level. We then explore the implications of selection when it is strong at the genic level.