Tishkoff Sarah, A.; Gonder Mary, Katherine; Henn Brenna, M.; et al. (2007). "History of Click-Speaking Populations of Africa Inferred from mtDNA and Y Chromosome Genetic Variation". Molecular Biology and Evolution. 24 (10): 2180–2195. doi:10.1093/molbev/msm155. PMID17656633.