McIntyre, M. H., Herrmann, E., Wobber, V., Halbwax, M., Mohamba, C., de Sousa, N., Atencia, R., Cox, D., & Hare, B. (2009). Bonobos have a more human-like second-to-fourth finger length ratio (2D:4D) than chimpanzees: a hypothesized indication of lower prenatal androgens. Journal of Human Evolution, 56(4), 361-365. doi:10.1016/j.jhevol.2008.12.004.