How many ethnic groups do they have ?
Ethnic groups differ from other social groups , such as subcultures , interest groups or social classes , because they emerge and change over historical periods ( centuries ) in a process known as ethnogenesis , a period of several generations of endogamy resulting in common ancestry ( which is then sometimes cast in terms of a mythological narrative of a founding figure ) ; ethnic identity is reinforced by reference to " boundary markers " - characteristics said to be unique to the group which set it apart from other groups .