Final answer:
Genetic drift and natural selection are the evolutionary forces that can drive divergence after isolation has occurred in a population. Gene flow and mutation can introduce new genetic variation but do not specifically drive divergence.
Step-by-step explanation:
After isolation has occurred, genetic drift and natural selection are the evolutionary forces that can drive divergence in a population. Genetic drift refers to the random fluctuations in allele frequencies that occur in small populations. This can lead to the fixation of certain alleles and the loss of others, increasing genetic divergence. Natural selection, on the other hand, favors individuals with advantageous traits, leading to the accumulation of beneficial alleles and divergence between populations. Gene flow and mutation can also introduce new genetic variation, but they do not specifically drive divergence after isolation.