What is the main conflict in The Bell Curve: Intelligence and Class Structure in American Life by Richard Herrnstein?

The Bell Curve is one of the most controversial works of social science in the 1990s and perhaps from the 1990s to the present day. Its major concerns are those of the relationship between intelligence, genetics and social trends. The history of intelligence testing has occurred mostly in the twentieth century, but various social scientific ideological trends have turned against intelligence testing in recent decades in part because it seems to yield politically disturbing conclusions.