Examine the following scenario: A population of small fish lives in a lake (Lake A).The dark-colored fish are the ancestral phenotype and represent the usual coloration of the species. The bright-colored fish, however, arose over time. There is a steady rise in the population of bright-colored fish. Both populations thrive. Suppose that a short land barrier separates Lake A from another small lake with a population of only the normal dark-colored fish (Lake B). After torrential rains lasting for days, the lakes overflow and a few of the bright-colored fish from Lake A are washed into Lake B. List the sequence of evolutionary mechanisms which have come into effect in each event.