the moreno category, but also almost half of the people who previously had identified as white, and half the people previously identified as pretos also choose the moreno category. According to a 2000 survey held in Rio de Janeiro, the entire self-reported preto population reported to have African ancestry. 86% of the self-reported pardo and 38% of the self-reported White population reported to have African ancestors. It is notable that 14% of the pardos (brown) from Rio de Janeiro said they have no African ancestors. This percentage may be even higher in Northern Brazil, where there was a greater ethnic contribution from Amerindian populations. Racial classifications in Brazil are based on skin color and on other physical characteristics such as facial features, hair texture, etc. This is a poor scientific indication of ancestry, because only a few genes are responsible for someone's skin color: a person who is considered White may have more African ancestry than a person who is considered Black, and vice versa. But, as race is a social construct, these classifications relate to how people are perceived and perceive themselves in society. In Brazil, class and economic status also affect how individuals are perceived. Conception of Black and prejudice In Brazil, a person's race is based primarily on physical appearance. In Brazil it is possible for two siblings of different colors to be classified as people of different races. Children who are born to a black mother and a European father would be classified as black if their features read as African, and classified as white if their features appeared more European. With no strict criteria for racial classifications, lighter-skinned mulattoes (who obviously were descendants of some Europeans) were easily integrated into the white population. Historically, Europeans took African women as concubines or sexual partners, resulting in mulatto children. Through years of integration and racial assimilation, a white Brazilian population has developed with more historic African ancestry, as well as a black population with European ancestry. In the United States, slavery became a racial caste, and children of slave mothers were considered born into slavery. The efforts to enforce white supremacy after the Civil War and Reconstruction resulted in southern states adopting a one drop rule at the turn of the 20th century, so that people with any known African ancestry were automatically classified as Black, regardless of skin color. At the same time, the United States