The authors argue that throughout much of the second half of the 20th century, race in the United States was often understood in social sciences like anthropology and sociology through the “ethnicity paradigm” or “ethnicity theory” (21). This view holds that different groups belong to different ethnicities, which are cultural in nature.

The ethnicity paradigm became mainstream by the 1940s, overcoming older biological theories of race. From this time to the 1960s, ethnicity theory was used by left-wing thinkers to promote a pluralist and assimilationist view of society where all ethnicities are accepted. However, by the 1970s, the authors assert that ethnicity theory was coopted by neoconservatives, who instead promoted a vision of a “colorblind” and “post-racial” society (21-22). Overall, ethnicity theory went into decline in the late 20th and early 21st centuries.

Before the rise of ethnicity theory, racial attitudes in the United States were based on two foundations: biological theories of race and Puritanism. Drawing on theories of evolution that emerged in the 19th century, biological theories of race held that alleged racial differences—including personality, intelligence, and sexuality—were a result of biology. Such theories came under increasing attack in the late 19th and early 20th century by black activists like W.