Having lived among gray tree squirrels and golden-brown fox squirrels throughout my life, I am always caught off guard when I re-encounter the black squirrels of northeastern Ohio during visits to my wife's home town. These melanistic variants of eastern gray squirrels are not isolated mutants but, rather, represent the dominant phenotype of their species.
When European explorers and settlers first arrived in North America, almost all eastern gray squirrel populations were reported to be black in color. Thought to have evolved as camouflage from predators when these agile creatures inhabited the dark, mature forests of the eastern U.S. and eastern Canada, the coloration has shifted to gray or gray-brown in the open forests, woodlots and suburban areas that characterize most regions today. Nevertheless, the black race of eastern gray squirrels remains dominant in many areas of the Northeast, from southern Canada to northeastern Ohio and northern Pennsylvania and from Michigan to New England. In some areas, eastern gray squirrels may harbor a mixed coat of gray-brown, black and white.
In all other respects, these racial variants manifest the same behavior and arboreal lifestyle and, as members of the same species, they are able to interbreed; their variable coloration merely reflects the outward expression of their genome (as does the hair color and skin tone of humans). Sexual reproduction ensures a serial mixing of their genes and, over many generations, natural selection determines the physical appearance of regional squirrel populations, retaining traits that favor survival within each ecosystem.