Nathan G. Alexander,Race in a Godless World: Atheism, Race, and Civilization, 1850-1914. New York/Manchester: New York University Press/Manchester University Press, 2019. ISBN978-1526142375
Eric T. Brandt, Timothy Larsen, "The Old Atheism Revisited: Robert G. Ingersoll and the Bible," Journal of The Historical Society, vol. 11, no. 2 (2011), pp.211–238.