 The divergence between "C. chilensis" and "C. nigra" probably occurred 6–12 million years ago, an evolutionary event preceding the volcanic formation of the oldest modern Galápagos Islands 5 million years ago.Mitochondrial DNA analysis indicates that the oldest existing islands (Española and San Cristóbal) were colonised first, and that these populations seeded the younger islands via dispersal in a "stepping stone" fashion via local currents.Restricted gene flow between isolated islands then resulted in the independent evolution of the populations into the divergent forms observed in the modern species.