In 2002. Peter and B. Rosemary Grant studied a population of Darwin’s finches on one of the Galápagos Islands that feed on seeds of various sizes. After a drought that caused only large seeds to be available to the birds, they found that natural selection favored those birds that had larger beaks and bodies. Once the rains returned and smaller seeds became much more abundant, however, natural selection favored those birds that had smaller beams and bodies. Which of the following processes is the BEST interpretation of this scenario?