In the late 1800s, people in many parts of the world decided to leave their homes and immigrate to the United States. Fleeing crop failure, land and job shortages, rising taxes, and famine, many came to the U. S. because it was perceived as the land of economic opportunity.
It is the result of a mutated message in your chromosomes. Chromosomes do not just determine how you look but they control all the processes of the cells in any organism.