CHRISTIAN, David. "Contingency, Pattern and the S-curve in Human History". World History Connected, [S. l.], v. 6, n. 3, 2009. DOI: 10.13021/whc.v6i3.4804. Disponível em: https://journals.gmu.edu/whc/article/view/4804. Acesso em: 11 sep. 2025.