Of particular note in the development of the hypothesis was the examination of thousands of human skulls by Samuel George Morton who argued on this basis that the differences between the races were too broad to have stemmed from a single common ancestor, but were instead consistent with separate racial origins. In his Crania Aegyptiaca (1844), Morton analyzed over a hundred intact crania gathered from the Nile Valley, and concluded that the ancient Egyptians were racially akin to Europeans. His conclusions would establish the foundation for the American School of anthropology, and would also influence proponents of polygenism.
