The Grand Canyon was carved out by the Colorado River. This caused the separation of members of a squirrel species. Abert’s Squirrel lives on the southern side of the canyon and in other parts of the United States. A subspecies, the Kaibab Squirrel, is found around the northern rim of the canyon and nowhere else in the country. As shown here, the two squirrels differ in body and tail coloration. Their ears are also different. These variations are the result of