Southern Europeans have North African genes

Southern Europeans are more genetically diverse than Northern Europeans. Geneticists have several different explanations for this phenomenon, one of which is migration from Africa to southern Europe.

However, previous studies, which have relied on samples from sub-Saharan populations, have not revealed much shared ancestry between Africans and Europeans. Recognizing that there are many genetic differences between Northern and sub-Saharan Africans, Carlos Bustamante of Stanford University and his colleagues performed a DNA analysis that included North African populations. Study shows high levels of shared ancestry between S Europeans and N Africans.

Population geneticists have formulated three hypotheses to explain the greater genetic diversity of Southern Europeans. One says that about 20,000 years ago, people from all over Europe retreated southward to escape advancing glaciers. When the glaciers receded, only a small segment of the original population recolonized the North.

A second explanation, associated with the Neolithic revolution and the development of agriculture in the Near East, about 10,000 years ago, is that people from the Near East migrated westward to Europe, with gene flow varying in different parts of the continent.

The third hypothesis says that Southern Europe's high genetic diversity was caused by recent migration from Africa to Southern Europe, related to the Roman conquest of North Africa and the Moorish occupation of the Iberian peninsula. However, previous studies suggested that Europeans and Africans share only between 1 and 3 percent of their genomes, making this scenario unlikely.

These studies looked at populations from sub-Saharan Africa but excluded North African populations. To correct this oversight, Bustamante and his team analyzed data from DNA samples of 2,099 individuals in 43 different populations, including seven from North Africa and three from Spain. They found much higher levels of gene flow from Africa to Europe than earlier studies had indicated.