The study of race and race relations has long been a central concern of sociologists. The assignment of individuals to racial categories profoundly affects the quality and even the length of their lives. These assignments are ostensibly made on the basis of biological criteria, such as skin color, hair texture, and facial features. Yet the biological meaning of race is so unclear that many social and natural scientists argue that race, as a biological phenomenon, does not exist. Others take the position that while different races exist, extensive interbreeding in many societies has produced large numbers of people of mixed ancestry. The assignment of these people to racial categories depends on social, rather than on biological, criteria. Thus the social consequences of biologically inherited traits is the fundamental issue of the sociological study of race.

Biological Conceptions of Race

While the terms race and ethnicity are often used...