When our long-ago ancestors left east Africa and spread to Europe, how did they get across the currently forbidding landscape of the Sahara? A recent analysis of Saharan plants shows that two peaks in the water-dependent plant population, indicating more favorable climate conditions, might have made human passage through the area easier. The first occurred about 120,000 and 110,000 year ago and another about 50,000 to 45,000 years ago. These dates fit fairly well with the fossil record. in particular, the biggest push out of Africa didn’t begin until around 50,000 years ago, and might have been facilitated by that second relatively wet spell.
The research itself is interesting: By analyzing dust that settled on the sea floor off the west African coast, scientists could examine the carbon isotopes in hydrocarbons from land plants and figure out which types of plants lived there when. (I’m always fascinated by these chains of evidence that start with painstaking examination of tiny relics of the past and reach up to encompass much bigger phenomena like major human migrations; this kind of thing is part of what made Jared Diamond’s Guns, Germs, and Steel so much fun to read.)
This article from the New Scientist has more details. The research was published as Wet phases in the Sahara/Sahel region and human migration patterns in North Africa, by I.S. Castañeda et al., Proceedings of the National Academy of Sciences, 106(48), 20159–20163, 2009.
