Compared with people in northern Europe, southern Europeans harbor a higher level of genetic diversity. Among the theories proposed to explain the difference in diversity, one hypothesis suggests genetic exchange between Africa and southern Europe based on the analysis of mitochondrial genomes that pointed to gene flow
from sub-Saharan Africa to Europe. Reckoning the geographic barrier of the Sahara Desert and the proximity of North Africa to southern Europe, a joint effort from IBE (CSIC-Universitat Pompeu Fabra) and Stanford University has reasoned that gene flow from Africa to Europe likely originated in North Africa. The authors analyzed genetic variations called single nucleotide polymorphisms, or SNPs, from 2,099 individuals in 37 populations across North Africa and southern Europe, and found that previous reports may have underestimated the shared ancestry between people in the two regions, if gene flow from North Africans, rather than sub-Saharan Africans, is taken into account. This North Africa influence have been mainly detected in the Iberian peninsula, in southwestern Europeans. In addition, the authors also found that the shared ancestry is unlikely to be the result of recent gene flow from the Near East into both regions Drawing on a database of disease risk alleles in populations from North Africa and southern Europe, the authors found that the genetic risk for most of 134 diseases among the populations was consistent with the authors' proposed migration pattern. According to the authors, the findings, which have implications for the accurate estimation of genetic disease risk in certain European populations, suggest that southern Europeans might share ancestry with Africans to a far greater extent than previously reported.

Reference article: Botigué et al. Gene flow from North Africa contributes to differential human genetic diversity in Southern Europe. PNAS.