The recent news of interbreeding between the ancestors of modern humans and some of their predecessors in Asia notwithstanding, the features we consider indicative of modern humans first appeared in sub-Saharan Africa, and the most genetically diverse populations now reside there. Nearly every aspect of the migration of these humans out of Africa and their interactions with other members of the Homo genus have been the subject of intense scientific debate. A paper that will be released by PNAS this week wades into that debate by arguing that the Sahara desert isn't necessarily a barrier to human migrations. As evidence, its authors point out that a number of fish species have made their way across the desert.
The basic premise behind the paper is pretty uncontroversial: at several points in the past, the Sahara has been humid enough to support abundant wildlife. These periods have been captured in everything from the fossil record to rock art left by humans during the most recent humid period. However, the potential for extensive human migrations across the Sahara during these times has been difficult to ascertain, leaving the Nile basin, which has remained a constant through various periods of climate change, as a potentially more appealing option.
The authors of the new paper, however, argue that the Nile has been a relatively minor contributor to the distribution of species in North Africa.
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