Olivieri, A. et al 2006. "The mtDNA Legacy of the Levantine Early Upper Palaeolithic in Africa". Science 314 (5806): 1767. doi:10.1126/science.1135566. PMID 17170302. "The scenario of a back-migration into Africa is supported by another feature of the mtDNA phylogeny. Haplogroup M's Eurasian sister clade, haplogroup N, which has a very similar age to M and no indication of an African origin".