 Such proto-racism and ethnocentrism must be looked at within context, because a modern understanding of racism based on hereditary inferiority (with modern racism based on eugenics and scientific racism) was not yet developed and it is unclear whether Aristotle believed the natural inferiority of Barbarians was caused by environment and climate (like many of his contemporaries) or by birth.Historian Dante A. Puzzo, in his discussion of Aristotle, racism, and the ancient world writes that