Race and ethnicity in Colombia descend mainly from three racial groups—Europeans, Amerindians, and Africans—that have mixed throughout the last 500 years of the country's history. Some demographers describe Colombia as one of the most ethnically diverse countries in the Western Hemisphere and in the World, with 900 different ethnic groups. Most Colombians identify themselves and others according to ancestry, physical appearance, and sociocultural status. Social relations reflect the importance attached to certain characteristics associated with a given racial group. Although these characteristics no longer accurately differentiate social categories, they still contribute to one's rank in the social hierarchy. A study from Rojas et al. involving 15 departments determined that the average Colombian (of all races) has a mixture of 47% Amerindian, 42% European, and 11% African.[2] These proportions also vary widely among ethnicities.