I had mentioned earlier that the volcanoes of the Virugna region in the Western Rift Valley (as well as other highland spots) have often been islands of rain forest separated from each other by different habitats, including grasslands and wooded savannas. this has produced an island effect that has been a laboratory for evolution, and it is likely that these forest islands (and others in the greater region of east Central Africa and western East Africa) have been the loci of evolution of many endemic species. (See Island Africa: The Evolution of Africa’s Rare Animals and Plants by Kingdon for an excellent overview of the Island Effect in highland regions of Central and East Africa.)

It is probably not a coincidence that two of the three subspecies of gorilla live within sight of each other (and of the main subspecies, the lowland gorilla) within this region. The Virunga volcanoes are not old enough to have supported island forests for the evolution of these specific subspecies, but other highlands in the region, or other volcanoes (perhaps in the Eastern Rift) may well have been the location in which they evolved.

And, as it turns out, there is reason to believe that the split between chimps and humans occurred on one of these volcanic mountain tops several million years ago. Or, at least, in an environment geologically similar to the upper reaches of the Virunga Volcanoes. But to tell this story right, I have to go back a few years.
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