A vast array of negative images and narratives about Black people, and Black Americans in particular, have been constructed and used in school curriculum to the effect of maintaining White supremacy in the U.S. Critical appraisals of African-descended peoples have been used to justify their enslavement and exploitation by Whites since the Enlightenment Era, as well as their continued struggles with poverty after Reconstruction. Elson (1964) provides a comprehensive analysis of U.S. textbooks in the 19th century. She makes note that the same Geography courses that taught that Whites were at the top of the racial hierarchy taught that Black people were on the bottom rung. Some textbooks spoke of Africans as lacking humanity except in their physical appearance, which even then was criticized against White norms. This type of observation extended to Black Americans too, since races were judged to be fixed categories at the time. Stereotypes that Black people were irresponsible, childlike, and naturally subordinate to Whites appeared in reading comprehension exercises and math problems in elementary school textbooks. In one textbook, an author wrote, "[n]ature has formed the different degrees of genius, and the characters of nations, which are seldom to change. Hench the negros are slaves to other men," thereby implying that slavery and other inferior positions in society were natural places for Black people.