According to mtDNA studies by Holden (2005) and Richards et al. (2006), a significant proportion of the maternal lineages of Somalis consists of the M1 haplogroup. This mitochondrial clade is common among Ethiopians and North Africans, particularly Egyptians and Algerians. M1 is believed to have originated in Asia, where its parent M clade represents the majority of mtDNA lineages. This haplogroup is also thought to possibly correlate with the Afro-Asiatic language family:

When did Richards publish his mtDNA research?