Answer:
Option B, Gene flow theory
Step-by-step explanation:
Gene flow induces genetic pool in a particular species of organism. It also leads to speciation and therefore allows species belonging to a particular species to mate and produce fertile offspring with distinctive genetic trait as compared to their parents.
This new set of genes created by frequent mating leads to creation of genepool. Genepool allows the fittest genetic trait to grow further so that the fittest individuals are produced and in this way the weak behaviour traits are lost with time.
Hence, option B is correct.