In 1994, researchers published a controversial book entitled the bell curve in which they implied that people from lower socioeconomic classes are poor because they are less intelligent.

In 1994, Richard J. Herrnstein and political scientist Charles Murray published a controversial book entitled the bell curve in which they implied that people from lower socioeconomic classes are poor because they are less intelligent.
According to them, the lower amount of intelligence make this people unable to compete with their smarter counterparts in the workforce, which keep them from climbing the economic ladder