We know that, long ago, our kin dispersed out of Africa through the Middle East many times but whether they crossed under a forest canopy or across a scorching desert has been a matter of fierce debate. The answer to this question matters because crossing through a forest would have been easy. Crossing a desert would have been hard and required technology, like pottery, to carry water. Now new work studying the fossils of the world's only poisonous rodent is revealing convincing evidence that forested corridors granted a pathway out of Africa.
Follow me, I know the way!
Image courtesy of Kevin Deacon.
The new work focuses upon the African crested rat, a bizarre species that rubs the sponge-like hairs on its back against poison collected from poison arrow trees to keep would be predators away. Found in the highlands of Kenya and Ethiopia today, these rats thrive in wet and densely vegetated woodlands where the poison arrow trees that they depend upon for protection grow well. Given that they are definitely not desert dwellers, the researchers were surprised when they realised that a whole bunch of rodent skulls that they had dug up in sediments of the southern Judean Desert were all an extinct subspecies of this very odd rat.
Fascinated by this discovery, the researchers used species distribution models to estimate the timing and location of habitats that would have been suitable for these poisonous rats to live in the region. The results suggest a brief period when forested corridors connected eastern Africa to the Middle East across the present-day Judean Desert, facilitating the dispersal of crested rats and, more importantly, our ancestors, out of Africa. This just published online in Proceedings of the National Academy of Sciences. My coverage of it in The Economist will publish shortly.