The Sahara was green and populated: the genomic tale of the human evolution
The history of the human movements across the Sahara desert is not only contained in the archaeological evidence of ancient Saharan settlements, but it also dwells in our genome.
This new perspective on the peopling of the Saharan desert was adopted by the international team coordinated by Fulvio Cruciani from the Department of Biology and biotechnology “Charles Darwin” of Sapienza University of Rome. The results of this study highlighted that the male gene pool of northern African populations was shaped by ancient trans-Saharan human migrations.
The study, published in the journal Genome Biology, represents an important step in our knowledge about the human evolution and, more specifically, about the role of the Green Sahara in the peopling of the African continent.
During the Holocene climatic optimum (between 12 and 5 kiloyears ago), the Sahara was characterised by a fertile landscape (and so it has been called “Green Sahara”), so it did not act as geographic barrier against human movements between sub-Saharan Africa and the Mediterranean coasts. In order to study the peopling of this region, the researchers used the high-throughput technology of next generation sequencing to analyse 3.3 millions of bases of the human Y chromosome in 104 subjects, which were selected after screening thousands of samples.
The analysis of the geographical distribution of the Y chromosomes allows to make inferences about past demographic events of our species. Through this approach, the research team found 5,966 genetic variants (51% novel). Analysing the distribution of these variants in 145 African and Eurasian populations, it was possible to identify massive human migrations, which took place across the Sahara (before the desertification) and across the Mediterranean sea.
“The Y chromosome - Eugenia D’Atanasio, first co-author of the paper, says – is transmitted from father to sons, giving a “male perspective” on the recent human evolution. The comparison between Y chromosome data and the results obtained from the mitochondrial DNA (transmitted along the maternal line) and from the autosomal chromosome (transmitted by both parents) showed a sex biased contribution on the northern African genetic variability, with the a recent female input possibly linked to the Arab slave trade and an ancient male input, dating back to the Green Sahara period”.
“This analysis - Beniamino Trombetta, co-author of the study, says - also pointed out massive contacts across the Mediterranean sea, involving ancient movements of the European and African populations from Europe to Africa and vice versa. This evidence shows that the contacts between these two regions have been always occurred since pre-historical times”.
This study revealed for the first time the genetic footprints of trans-Saharan human migrations, which have been so far only hypothesized by the analysis of the material culture. The proposed scenarios contribute to a better knowledge of the recent human evolution and pave the way to new research lines about our history.