the exchange of genes among populations or species either by means of migration, or less directly by the diffusion of genes over many generations. Gene flow tends to limit the establishment of genetic distinctiveness. While it is relatively rare in isolated populations, when it happens it can be a highly significant event such that it can break adaptive gene complexes formed by genetic drift and alter allele frequencies
. See Allele, Founder effect, Genetic drift (or random walk), Phyletic gradualism and punctuated equilibrium, Speciation, Theory of natural selection