Answer;
Gene flow
Gene flow is the most important factor that holds a gene pool of a species together and prevents speciation.
Step-by-step explanation;
-Evolution may occur as a result of genes being transferred from one population to another. This gene flow occurs when there is migration. The loss or addition of people can easily change gene pool frequencies even if there are no other evolutionary mechanisms operating.
-Gene flow may also occur without migration, for instance, when people travel to another area and successfully mate with people in the population there, a transfer of genes occurs between the populations even though the traveler returns home.
-Additionally, gene flow may flow between species. A good example is when segments of DNA are transferred from one species to another by viruses as they invade the cells of animals or plants.