A population that has been isolated, especially a smaller one, could have a high level of homozygosity and therefore not a lot of genetic variation. Gene flow between such populations can increase the level of heterozygosity, and therefore up genetic variation.
B is the correct answer to your question
Increases genetic variation, which in and of itself has extreme benefits such as protection against disease, capability to evolve, etc
Astrology is not a main are of science
Region A, Hope this helps.
