Rosemary and Peter Grant describe highlights from their 30 years of field research in the Galápagos, citing evidence for populations at different stages of allopatric speciation, including "bumps on the road" that are completely understandable and even expectable based on our growing understanding of the evolutionary process. The Grants' observations go far beyond simply noting that the birds are well-suited to their ecologies--that much does not require a prolonged study period.
Your task in writing on this topic will be to identify and delineate those parts of the Grants' results that document each of the following phenomena:
evolution by directional selection
evolution by genetic drift
pre-zygotic and post-zygotic reproductive isolation
breakdown of reproductive isolation (introgressive hybridization)
evolution involving non-genetic inheritance (cultural inheritance)
Sample Solution