Many studies of African genetic diversity have concentrated on sub-Saharan and northeastern Africa, the most likely source region and corridor to the rest of the world (Tishkoff and Williams
2002). North Africa, however, may have followed a distinct evolutionary direction and requires further investigation. Genetic studies of this area, performed using classical markers, have revealed an agreement between genetic and geographic distances (Cavalli-Sforza et al.
1994) and a predominantly east-west structure to the genetic variation (Bosch et al.
1997). A compilation of 185 mtDNAs sampled across North Africa showed (1) that about half of the lineages belonged to the L haplogroups otherwise observed mainly in sub-Saharan Africa and (2) that most of the rest fell into haplogroup U6 (Salas et al.
2002), which perhaps originated in the Near East and spread into North Africa ~30 thousand years (KY) ago (KYA) (Maca-Meyer et al.
2003). Y-chromosomal studies are potentially highly informative about the origin of male-specific lineages, because of the detailed haplotypes that can be obtained and their high geographical specificity (Jobling and Tyler-Smith
2003), but previous studies have been restricted to limited regions of North Africa (Bosch et al.
1999,
2001; Flores et al.
2001; Manni et al.
2002; Luis et al.
2004). Together, these genetic analyses highlighted the similarity between northeastern Africa and the Middle East and the clear genetic differentiation between northwestern Africa and both sub-Saharan Africa and Europe, including Iberia. The Sahara and Mediterranean, despite the narrow width of the Strait of Gibraltar, seem to have acted as effective long-term barriers to Y-chromosomal gene flow.
A Predominantly Neolithic Origin for Y-Chromosomal DNA Variation in North Africa
