Race is a social construction, an idea that has been created and accepted by a society. The idea of race is based on physical traits. However, different cultures have different understandings of race. For example, many individuals who would be considered black in the United States would be considered white in Brazil. Over time, these cultural definitions can change. In the 19th and early 20th centuries immigrants from Greece, Italy, and Slavic countries were not considered white. By the late 20th century people of Greek, Italian, and Slavic descent came to be seen as white.
Historically, racial categories have been defined, in part, by the region of the world in which a race originated. People whose ancestors hailed from different parts of the world do differ in some ways. Thousands of years ago, populations developed physical characteristics that helped them survive in their various environments. For instance, consider the skin pigment melanin, which helps protect against sunburn but also inhibits the production of vitamin D. Populations closer to the equator, where the sun is intense throughout the year, evolved skin that contained more melanin. Populations in northern climates, where the sun is less intense and winter days are very short, developed skin containing less melanin. In modern society, people can wear sunblock and take vitamin D supplements, and variations in skin pigment have little effect on survival.
There is no fixed set of physical characteristics that can adequately define a race. The physical variation among members of the same race is greater than the variations between races as a whole. People who identify as white can have blond, red, brown, or black hair. People within any perceived race can have light or dark skin. Some people who identify as black have lighter skin than others identified as white. Recent advances in DNA sequencing have shown that genetically, human beings, regardless of race, are 99.9 percent the same. Tiny variations in DNA are responsible for superficial physical characteristics such as skin color. At the genetic level, race does not exist: there is not a gene, or a set of genes, that defines any race. It is important to note, however, that although race is a set of socially constructed categories, the idea of race and how it is used in social life has very real consequences. In the United States, having white skin confers numerous privileges. These privileges impact social behavior and social experience. Studies show that these discrepancies occur in a wide range of situations. Ideas about race mean that when people of color walk through a neighborhood, their presence is not interpreted in the same ways that a white person's presence is. Residents are much more likely to call the police or make informal reports on social media when they see unknown people of color in a neighborhood. Black drivers are much more likely to be pulled over by police than white drivers. Job applicants with names perceived as sounding African American are less likely to be contacted for interviews than are applicants whose names are perceived as sounding white. Thus, while race has no biological or genetic meaning, it has enormous social meaning.
Racialization is the process of imposing racial distinctions on individuals or groups. In the past, scientists tried to define races. Some identified three races, others identified five, and others many more. Concepts and definitions of race have changed over time, but serious investigation has proved that humans' physical variations do not fit into rigid racial categories. For instance, in the United States, people who have a black parent or grandparent have historically been classified as black, even if their other ancestors are white. This reflects the one-drop rule used in the South before the American Civil War. The one-drop rule was a social and legal principle in the United States that proclaimed that anyone with even one drop of so-called "black blood"—any known African ancestry—was considered black. In the 19th and early 20th centuries, many European immigrants in the United States, including Irish, Italians, Slavs, and Jews, were not considered white. Definitions of race also vary from place to place. Today, a person with mixed-race ancestry who might be considered black in the United States, based on physical characteristics, might be considered white in many Latin American countries.
Sociologists analyze the social construction of race––how a society defines race, and what race and racial identities mean in a society. Although definitions of race change over time and vary across societies, race and racial identity are important factors in social structure and in the lived experiences of individuals. Racial classifications, ideas about race, and the history of racial discrimination play significant roles in societies across the world.