Macroevolution is the evolution of species and larger groups. This requires genetic variation leading to phenotypes on which natural selection can operate. Gene flow can bring new versions of genes into a population, allowing new genetic combinations and new phenotypes to appear, while genetic drift can greatly change alleleic frequencies. This also can alter what phenotypes are present for natural selection to act on, leading to the appearance of new species.
Work Step by Step
Review the definitions of all of these concepts in earlier chapters, and think about how they can change genotypes/phenotypes. Remember that natural selection acts on phenotypes, but these are directed by the genes operating in an organism.