This is due to various factors such as economics, upward mobility and educational opportunities.
When this occurs new communities develop, form and branch out spawning a growth in population and migration. As the various traits from one’s genetic makeup mixes with others of another makeup, this helps to further expand the world’s unique makeup among its various populations and cultures. As these factors come into play over and over again, this helps to ensure the possibility of cloning one’s self or someone else will never happen.