(Photo credit Nils Hagar, World Wildlife Fund, via the NYT)
Evolutionary "hotspots," as they are called, arise in regions that have been geographically isolated and environmentally stable for very long stretches of time. Under these conditions, populations tend to evolve characteristics that set them far apart from neighboring populations outside the "hotspot," and with diversity not found elsewhere.
The Eastern Arc Mountains of Tanzania comprise one of these hotspots. For example:
In 2005, for example, scientists discovered a new species of monkey, a slender, tree-dwelling primate called the Kipunji. At first it appeared to belong to a group of monkeys called mangabeys. But last year scientists studying its DNA were surprised to discover that it was not a mangabey at all; its closest kin are actually baboons.The New York Times' Carl Zimmer has the coverage. Read it all.