The central chimpanzee sequences also appear to be the oldest of the chimpanzee lineages.
From the sciencedaily.com
Bonobo and chimpanzee territories in central Africa are close to one another and separated only by the Congo River.
From the sciencedaily.com
Most of the variation in the chimpanzee sample comes from the central African chimpanzees, with the least amount of diversity found among the western chimpanzees.