Out of Africa - a new route?

The widely held belief that the Nile valley was the most likely route out of sub-Saharan Africa for early modern humans 120,000 year ago is challenged in a new paper in the Proceedings of the National Academy of Sciences.

A team led by the University of Bristol shows that wetter conditions reached a lot further north than previously thought, providing a wet 'corridor' through Libya for early human migrations. The results also help explain inconsistencies between archaeological finds.

While it is widely accepted that modern humans originated in sub-Saharan Africa 150-200 thousand years ago, their route of dispersal across the hyper-arid Sahara remains controversial. The Sahara covers most of North Africa and to cross it on foot would be a serious undertaking, even today with the most advanced equipment.

Well-documented evidence shows there was increased rainfall across the southern part of the Sahara during the last interglacial period (130-170 thousand years ago). The Bristol University team, with collaborators from the universities of Southampton, Oxford, Hull and Tripoli (Libya), investigated whether these wetter conditions had reached a lot further north than previously thought.

Anne Osborne, lead author on the paper said: "Space-born radar images showed fossil river channels crossing the Sahara in Libya, flowing north from the central Saharan watershed all the way to the Mediterranean. Using geochemical analyses, we demonstrate that these channels were active during the last interglacial period. This provides an important water course across this otherwise arid region." The critical 'central Saharan watershed' is a range of volcanic mountains formerly considered to be the limit of this wetter region.