Donges, J. F., Donner, R. V., Trauth, M. H., Marwan, N., Schellnhuber, H. J., & Kurths, J. (2011). Nonlinear detection of paleoclimate-variability transitions possibly related to human evolution. Proceedings of the National Academy of Sciences of the United States of America (PNAS), 108(51), 20422-20427. doi:10.1073/pnas.1117052108.